lOll 1000
10.000
100
000
1
000 000
-'~·11!tl'·'-I'!·I·I'!·!'!·I·I'!II'O~!

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L

< 4

'
CAPACITY.
IN
CFH
WITH064
5P
GR
GAS


n
+,
I
~/II;
~/
,
FIG.
8-
PRESSURE DROP
VS.
CAPACI'N
FOR
A
'NPICAl
BUlTERFl
Y VALVE.
MAXIMUM
OPENING
ANGLES
SHOWN 'ARE USEO
AS
TRIAL SETTINGS WHEN AOJUSTING VALVES FOR HtGH FIRE.
sure regul!'llor
oullel
pre,ssure
by
O~
in.
\Of<:
to

allow
for
the
additional
pressure
drcp
across
the 2 inch SSQVs.
This requires
estimating
a new pressure
dfcp
for the
pressure regulator.
SSOVs
and
Firing
Rate Control, plus
repealing
the
sizing
procedure.
SIZING CHART FOR FIRING RATE
CONTROL VALVE
Butterfly Valves
are
otlen
used
for
Firing Rale Control

Valves. SinCe a Butterfly Valve
ctleS no! provide
light
clo-
sure, a safely
shutoff
can!rol valve (SSOV)
must
be
used
l4)slream.
Inaddilion
101M
buUerlly control valve size, we neeO
10
know
lhe
mallimum
QQenino
angle
(in degrees)
U'OOd
as a
trial
selting
when
adjusting
a BUllerfly Valve
to
hi~

fire.
In our
ellample.
the
eslimaleO
pressure
drq:J
across
the
liring
rate control is 6.5 inches
wC
wilh
a capaCity
of
10,500
294
cfh at
standard
conditions.
a. If
SSOV
estimaled
<md
actual pressure
drop
are
lha
~.
Mark

the
intersection
oflhe
estimated
Butter-
fly Valve pressure drq:J and capacity, X
on
Fig. 8.
Use
Ihe
valve size
and
opening
angle
indicaled
IYy
lhe
nearest
slanted
line below
X.
In
this
case, ar;ply·
ing
the
estimated pressure drq:J
results
'n a 2
inch

valve
wHh
a
mallimum
opening
angle
at
45 degrees.
b.
If
SSOV
aclual
pressure
droo
is less
than
lbe
esli·
malad
pressure
droo.
Add
lhe
pressure drq:J difference (0.8 inch we)
to
the
pressure
Orq:J
available
for

the
Bullerlly
Valve.
0.8 + 6.5
'"
7.3 in.
we
Mark the intersection 017.3 in. wc
and
lhe capacity
y,
Use
the
valve size
and
opening
angle
indicated
by
lhe
nearest slanteO line below. In
lhis
case, we have a 2 inch
valve
with
a 40 degree opening.
V5055
VALVE
SIZING
NOMOGRAPH

" "
,
'r
,

i
VAL\I~
sin
,.
J
,
,
,r
.,
'Rf~1U1U
ORO'
"'
"

,.
we

.,
LO
,.
;

,.
; .
,

1
,.
l4UOO
V5055
VALVE
100.000
SIZING
CHART
J'!C'~'C
CIlA"'TY
COIlAtel'ON
,
,
•
,
•
,
"
•
lUDD
"LlHi:<
·
,
0
.IlUSUllli
<'II
G

, (I
·

,
HD~
"
,
,
"
0
,
•
"

•
·
•
,
•
"
1.000
,
t
·•
•
,
•
, ,
,
,
RfOUIRW
>


fOA",,,
TID"
T,,,,
01
0

•
•
;00
·
,
"
s ",«o
·",
_.
0
Bu,"o'
G.
Cl~
. _
·
•
,
, "
rc'"·
8",,0,
~
O'olf,l,
\I5"~S
Inl.'

'
'.1
,,",,
,
·
,
,
•
V~5
Ou''''
Ro"""
P,."y'"O,""'oco
I
0",.1'
"
"
'"
.
•
,
_

,"

,
"',
__
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,-,


__
,n
w'
'P

,""
d.".
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"~,
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,,,
••
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.,

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,

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Yl
o.~

,".
So>o."f",.~


No .,,5055
I
INITRuCT<CNI
Non,
II
",,",.1

' "1'0.,10<
."

" 0."1
,,~ o.
J.
Dr
I
G)
''0'"
··C~"
~

'0
,k'Q
,,_
on
••
nd
,

'


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"t.
,~.
.1'r " D'QQ·· c "
_,
I,.,"
,.<h
""
'0
0
',n.
0
',,,,,,.I,,
_
··S

«'«
<;",,'.
II_

)-l"
r:o,
',Qn"
'0
'

""'d
"Clh
G_

fh

:·
Dr
I;.,
~
''0"'
"B.,n",
Clh,"
'h,,,,,"
D.,.,,,,,,
'J)
,.Q
·"

<,(OO.~.,,'"'··O'

'"_
,
"oeM.
01
101
"d
I,,,,
@ . ,

1

So


,'·
__
"",n'
"II,
bo,_.n
, ,
.>0

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, _

'~"""'''Q_
aI
t,""
(!)
."d
101
'0

'
··

C",··
,.t

,
'h'
t"

,

0"',
The correct size V505 5 Industrial Gas Valve can
be
quiCkly selected
usinog
this nomograph. The nomograph is
available in pads
at
25 under form number
70-86.27.
Tha
1oll0winog
8)(amples show how to use the VS055
Valve Sizing
Char1.
EXAMPLE
1
These
are
the specifications from
our
original example:
Type
of
Gas
Milmd
SpeCifiC Gravity 0.72
sp
gr
Gas Flow Capacity 7.200,000 Btuh

Heat Content
of
Gas 800 Btu per
Cu.
fl.
Estimated Pressure Drcp across V5055
Single Valve 12.2 in.
we
2 Valves Piped in Series 5.5 in.
we
295
For this chart, we need to know the inlel and outlet pres-
sure for the V5055.
1.
Determine inlet pressure for V5055. When 2 valves are
used,
lind the inlel pressure
of
the first
valY'6.
From Fig.
2 we see thai the V5055 inlel pressure equalS the pres-
sure regulator oullet pressure less
lhe
piping pressure
loss from the pressure regulator outlet to the
V5Q55
il'l-
Ie!.
Find the piping

lOSS
flQJre tram Fig.
3.
It
we
haY'6
5
leet
at
2 incll pipe,
tM
pressure
drcp
will
be
1 inch
wc.
Regulator Outlet Pressure - Piping Pressure Drcp
= V5055 Inlet Pressure
27.6 in. we - 1 In. we
= 26.6 in.
WC
2.
Determine tile oullel pressure for V5055. The outlet
pressure equals lhe inlel pressure minus the pressure
drcp
across the valve.
71·97558-1
,
•

vuv£
SIZE
,
"'
PAE~~lJAE
ORO'
",
"
'"
Ito

ltuoo
101.090
"'
V5055
VALVE
SIZING
CHART
EXAMPLE
1
SPH'FIC
G~""'TY
COIIIIECTlO

•

Dc
TUT
PRESSURE
IPS'

~"UGEI
"
'"
"
,
,
r
~
t
~
~
• 8
f
~
,
,
,"
,,
!
"'
•
,
•
,
1
.00i
'"
".
".
"

o

"
"
"".
·
,
Inlel Pressure - Estimated Pressure Drcp
'"
Oullet
Pressure
26.6 - 12.0 = 14.6 in,
we
NOTE: Since we calculated
the
corrected capacity
under
standard
conditions, 10,370 cfh.
we
can skip
lines 1 and 2
In
lhe
1,'5055
Valve
Sizif'l;l Chart
direcllol"6.
3.
Draw line 3

from
14.6
inches
we
on
the
Outlet Pressure
scale
10
12.0 Inches
we
on
the Pressure
Prep
scale.
Since Qutlet Pressure scale
is
In
psi un/Is, multiple 14.6
inches we by (he conversion 1aclor1rom
IheAPPENPIX
10
gel the
correct
psi
unl!.
14.6
)(
0.0361 = .527 pst
Draw line 3

from
.527 psi on QVllel Pressure scale
\0
12.0
Pressure Droo scale.
4.
Draw
line
4
trom
10,370
cfh
on
the
Burner
CFH
Gas
Flow caoacity scale through intersection
of
Ml
and
line
3,
fa
the valve
site
scale
12
inches).
EXAMPLE 2

Determine the
1,'5055
Valve
sizQ
from lhis job's
5j:lElciflcations:
capacity
7,500,000 Bluh
Type
of
Gas
Prcpane
Specific
Gravity 1.53 spIJr
Heat Conlent
of
Gas
2,500
Btu/cu. ft.
Inlel
Pressure Available
at
1,'5055
13
Inches
wC
Eslimated Pressure
Drop
across
1,'5055

7 inches
wC
OJtlet Pressure al
1,'5055
6 Inches
wc
••
SOLUTION
calculate
cfh required.
7,500,000 Btuh - 2,500 Btu/cu
ft
'"
3,000 cfh
1.
Draw line 11rom 0.64 on "SpecifiC Gravity
Correclioo~
'scale
10
3000 on "CFH
Gas
Flow·
scale.
2. Draw line 2 tram 1.53 on -SpecifiC Gravity
SCare,~
through interseclion
of
line 1 and M2,
10
•

Bl,rrner
CFH
Gas Flow." This is the adjuslecl
gas
110w.
3.
Draw line 31rom I) inches
we
on Outlet Pressure scale
107
inches
we
on the Pressure Droo scale. Since the
Outlet Pressure scale is in
psi units, mulliply 6 inches
we
by Ihe conversion taclor
In
(he APPENDIX to get psi
units.
6 In.
we
)(
0.0361
'"
.216 psi
4.
Draw line 4 from adjustecl
gas
flow

on Bumer
CFH
Gas
Flow scale
(hrou~
Ihe
inlersection
of
line 3
and
M1
to
the Valve Size scale
(101/2
Inches).
,

,

"'
V5055
VALVE
VALVE
SOl(
P~E~SU~l
IOU"
SIZING
CHART
OAOP
"'

EXAMPLE
2
,
SPlt."C
"
.,
eRA
V""
CORR!tno


,.
,
,.
,
~
"
;

,1
,
OuTLET
PRESSURE
'PS'
GAuGll
'"
•

,


r
,.,
,.
,,
,
".

!
·
~
,
•
~l
~
,
1.000
•
,

,

,
297
71·97558-1
APPENDIX
CONVERSION TO STAHDARD CONDITIONS
STANDARD CONDITIONS
-"'061 valve sizing charts
provide
coordinates under a

sal
of
slandard conditions.
This
allows systematic selec-
tion
of
gas
valves for various applications. These standard
corditlons
are:
1.
Capacity -
cubiC;
feel
per
hour
lcfh). ConverSion
10r-
mula on
page
14.
2. Specific Gravity - 0.64 sp gr.
3.
AWtude
~~sea
level.
CONVERT CAPACITY TO
0.64
SPECIFIC GRAVITY

4.
Pressure Drop - , inch walEir
column
(lin.
we)
across
valve.
These condilionsare seldom
fOUnd
on
an actual job. To
use the valve sizing charts,
we
must convert the jd:l condi·
lions
in this BKample to the equivalent cfh gas rating under
the standard conditions.
CONVERT
CAPACITY
IN
BTUH
TO
CFH
CftJ
= Bluh
Btu/cu. ft.
CONVERT
CAPACITY
TO
0.64

SPECIFIC
GRAVITY
HOW
TO
USE
CHART
Listed valve·capaciTy
ratino;:;
~re
based on
O.6'llp
gr
9U.
W})en
the required cfh
""pa";I~
is kncwn (or
911
of other
specific
<:IfavitY.
it can
be
convened
to
the 0.64
'p
g<
tQw~al~nt
by use

of
correcl multiplying faclor Obtained from
this charI. Example; A
nfve
capacity of
2670
cfh
blwd
on 0.72
lp
<:If
gax
is
~C1ui~d_
Whit valve capacity based
on
0.64 sP
\IT
","S
will be nlCluved? Solution: On
wrtSul
sc.&Ie
of
chart. find 0.72 sp
gr.
From
that
point, move horitonlillly
10
ri'ilhl

10
intenecl
the
cUJVe;
lhen
move Itn.ighl down
10
bottom
seale and
!ud
lhe conversion factor, 1.06.
Mwtiply the
2670
cfh by the
conve";"n
factor: 2670
dh"
1.06 = 2830
d'h.
When the
raled
capaeity
of
ill
ulve
ror 0.64
'P
\IT
gas
is

'b1own.
ilS
equivalent Cap'C)ty for 'l"" of
other
<peeific
gravity may
be
determined by dlvidinq the raled capacitY by Ihe conversion
faclor.
ElIa~
The rated capacifY
of
II
cenain
valve is
3500
cFh.
What is
ill;
equivalent capacity
lor
0.72
lp
\IT
gas? Soluticnc
3500
cfh
~
'"
3301

cFh.
I
,
I
i
,
i
I
::~~ !:_-:-4
Y
I
/
-
,
c~
i
i
,
I
'D'r
'"
I ,
,
I
I
,
/
I
'''C_c
~,

__
+-_-'-_, _~
+_-~.L ~ c
,,
I
I
iii
I
I
,
I
/'
I
I
~-_-_
i
''',-_c
~-~·~~~i~·-!C-I-+-I +,I_-_-_-+,,'-_-_-+-!C-_ ;;-;'I/i:~~,::=~~~:~_-+-,-_-_-
,
r:
L
Yi I I
,c
- . I Y i
I
,
L.Ce~I~"'.=i=~
~~;;-f-/ t-
O.7:>f
I-t t r t t J t-

,
!
/./
I I
1
o~o
l +-7"l"'~ i-++ + + + + +-
I !
,
!
i
I
I ,
"'f +-!i-!-~ +i
-UE:,
=:1
=:i
=='f l~:~:: ;,
I
i
L l._
"" ~O"' ~'~'-~-'Oc", Cl.o
1.1
u'
n
I
'-:>
i
c,
i

c
'
'c,
'0
CO""V[ltSIOo,r
faCTORS
"
To
find
cFh
itt
.64
op
gr,
mwtiply
cfh
at
"x"
,p,
qt,
by conversion factor.
iD find
"Fh
at
"J<"
sp
qt,
divide
cFh
at

.64 "p.
gr.
by conversi\ln faclor.
>.11

298
CONVERT
CAPACITY
TO
SEA
LEVEL ALTITUOE
CONVERT
CAPACITY
TO
SEA LEVEL ALTITUDE
HOW
TO
USE
CHART
When required valve capacity
in
cfh
at
sea levrl is known. lilt equivaltnl rtquinod capacity at hiqher elevationJ
r.1ay
be dele,mined by
use
of correct multiplyinq factor obt.tintd from litil chari.
Example: A valve
capaaty

or:sooo
dh
ill required
It
5

ltvel. Whll would be the required capacity at an
elultion
~t
above sea lewl?
Solution:
On
vertical scale of chart, find 4550 ft. From lhat point,
move
horizontally to riqhl to intersect lile curve;
lilen move straiqht down
to
bottom scale and read lile conV'trslon flctOt, 1.087. Multiply Ihe 3000 cfh by lil. factor;
3000 cfh
ill:
L087
= 3261 cfh.
NOTE: To find the capacity at sea
level
when the capacity
at
I hiqhet eltvation is known,
~
the known capacity
by the conve,.,.jon factor.

3261 cfh =

00
1 087
~ cfh,
7000
60QO
2000
1000
,
I
r.,
,
, ' : :
J'
.

.
, ,
,
H
, ~
, -
,='
I J_.LLL

_c.;

:
+-i

,
, ' ,
-
,~
, -
: ,.
, '
:
+-
o
1.000
I.oZO
1.060
1.080
1.100
CONVER910"
FACTO"
1.120
1.140
,",60
Ja

299
71-97558-1
PRESSURE DROP CONVERSION
10,000 cfh
10,000 cfh
==
5,000
cfh

;
4 in. wc 2
This conversion
IS
nol
otten needed because
rf105t
valve sizing charts list a range
01
pressure
drops
In inches
When
lhe
pr9SSUre
drCll
is
raled in
pounds
per
square
wc.
I-fOWever.
if
a chart is
not
available, divide the
cft1
by
inch

(PSij.
kilOQfams
per
SQJ8re
centimetre (kscj,
or
other
the square root
01
the available pressure drop in inches
pressure units, mUltlplV
by
known
unit by the conversion
wo.
factors below.
CONVERSION
OF
PRESSURE UNITS
(Convert by multiplying value
in
known pressure units by
laclor
lisled under required pressure
unit)
KH0WN
PRESSURE
UNIT
REOUIRED PRESSURE UNIT
POUNDS

PER
SO. IN.
OUNCES
PER
SO. IN.
MILLlMHRES
0'
MERCURY
KILOGRAMS
PER
sa.
CM.
INCHES
0'
W,o.TER
INCHES
0'
MERCURY
FEET
0'
W,o.TER
CENTIMETERS
0'
WATER
Centirnel8J11
of
Water
0.0142
0.227
0,735

0.000999 0.394
0.0289 0.032& -
F",
r:A
Water
0.433 6.94
22.4
0.0305
12.0
0.883
30.5
Inche6
of.
Mercury
0.491 7.86 25.4 0.0345
13.6 1.13 34.6
Inches
or
Water 0.0361 0.578 1.87 0.00254
00735
0.0833
254
Kilograms
per
sq.
em.
14.2 228.0
735.0 394.0 29.0
328
HXXlO

Millimetres
01
Mercury 0.0193 0.308
0.00136 0.535 0.0394 0.0446
US
Ounces
per
sq
In.
0,0625
3.2:4
0.00439 1.73 0.12:8 0.144
440
Pounds
per
sq.
irI,
16.0
51.7
0.0703
2:7.7
2.04 2.31
704
Absolute
Pressure
=
Gauge
Pressure + 14.74
psi.
tf

lhe
available pressure drop across the valve was 1/4
.25 psi x 27.7 (conversion factor
for
inches wc) =
psi, the equivalent pressure
in
inches
wc
would
be:
apprOXimately 7 in. wc.
'
300
PART
I-FIRING
RATE
(COMBUSTION)
CONTROL
INTRODUCTION
DEFINITIONS
1119
firing
Crate
is
Jhe
combustion rate.
II
is the rate at
which air, fuel, or snair-fuel mixture

Is
supplied
loaburner
or
furnace. It
may
be expressed in volume (cubic feel
of
gas
or
gallons
of
oil), weight (tons
of
coal), or heal units
(Btu's) sul=9lied
par
unit
lime
(usually
per
h::lur).
FirinrJ
rate
control
(or
combustion
control)
is
simply a

means
of
regu-
launQfUel supply, air supply,
and
the
ratioofairto1uelsup-
ply
according to load dernard.
PURPOSES
Automatic
Mng
rate conlrols are offen used
10
$illl'Jify
operatioo
and
to relieve operators from tedious monitoring
dUlies. However, their primary purpose is
lor
economy.
To
proouca Ihe mosl economical ep8ralion, lh&cOIltrol
system must mainlaln the air-fuel ratio at an optimum
value over the entire load range. Usually,
The
system must
also
control
other

imp::msnl facfOfs such
as
steam pras-
sure, furnace draft, waler level.
and
steam lemperature.
It
is
virtually impoSSible
for
an
operafor to maintain the pre-
cise
control necessary to achieve the gteatest
econany.
FACTORS
AFFECTING
THE FIRING RATE
Although the actual neaullQ
load
pfaceQ on the plant
is
the primary consideration. other faclors also affect the fir-
ing ral&. Since ducts, pipes,
and
flue passages
absorb
much
of the lotaf heal produced, opening
and

closing
lhem
in
ditf~rent
palterns varies the heat
loss
immensely.
The pickup demand
or the furnace or boiler also con-
sumas part of the heat output. When a bJrr.er syslem is
started, the mass of metal that comprises me furnace or
bOiler
absorbs a great amount
01
heat before all)' enters
the system,
and
it also radiales a portion of the heal
10
lhe
surrounding surfaces. Finally, lhe efficiency
of
the fUrnace
or boiler ilself has a bearing on the
amOl.n1
at fuel that is
burned. The efficiency depends to a great exlent on the
he-at
transfer qualities of the boiler or furnace.
LIMITATIONS

ON
THE
FIRING RATE
Turndown is lhe ralio or tna maximum firing rate (high
fire)
10
Ihe minimum /iring rate
(Jaw
fire)
al
which a burner
will operate satisfactorily.
It is also expressed as the range
of
firing rales over which satisfactory combuslion can
be
obtained. For
ax~le,
lhe firillQ rale
01
a burner with a 4
to
1 turndown range can
be
varied from
ils
maximum (100
pl3rcent) clown to 1{4
at
ils maximum (25 percenl), A high

turndown ralio
Is
particularly desirable
for
batCh-type fur·
naces or others
lhat
are shut down periodically. A high fir·
ing rale
can
be
usecs
to
Mal
lhe
furnace rapidly after
il
is
started
up
again. After the flIrnal:e is heated
up,
the firing
rale can be turned
down
10
normal.
Flame t::Jow-off limilS the maximum firing rate. A Ilame
moves away
from a burner when the velocity at lheair-tuel

mixture is greater than the
velOCity
Of
the
Ilame front (flame
propagation rate). Blow-cff often resuHs
in
the flame
being
extinguished.
Flashback limils the minimum firing rate. A flame
movesbaCk ""rough a burner
land
possibly
back
fa
theair·
fr el
mixinQ lXlinl) when
the
flame propaoation rale is
grealer lhan the velocity
of
the entering alr'fUel mixlure.
DRAFT CONSIDERATIONS
Drat!:
is lhe movement of air into and through a
CON'Ous-
{ion cflamber, brEl8ctling. stack, and chimney.
Natural draft results from the difference in density

of
the
heated air rising through the slack or chimney and the
COOler
displacinQ air.
Mechanical
draft is crealad try
mao
chinery, such as a fan
or
blower.
Types
of
mechanical
draft are forced and
indUCed
draft.
Forced draft is produced
by
a
fan
or
blower located at
lhe inlel air passage
10
the combustion charrt:lel'. Induced
draft is produced
by
a partial vacuum
within

the
corrous-
tion chaiTtler, created
by
a fan al the outlet at the
cMlTtler.
Natural draft
depoflds
on
ma",.
variables.
$Uch
as
1hE!
temperature of
the
atmosphere, height
Of
the stack, direc·
tion and force
Oflhe
wind, and other environmenlal condi-
tioos. Blowers or fans supply a conslanl draft lhat is
independent
01
these conditions. Therefor'll, mechanical
draft is used as the main source
of
air.
Every tiring rale

and
type
01
fuaJ
fequirss lhe
prcper
amount
01
draft for best results.
1he
draft
that is
needed
also
depends
a lot
on
Ihevolume
ofth'll cO'T'Ouslion cham-
ber.
Da"l)f¥s
in
tl"l&
air
passages are
use::llo
control the
draft. Darrpar p::lSilions are varied as tne firing rale is
varied.
FIRING

RATE
CONTROL
METHODS

In large plants, mothodl;
of
regulating the firing rate are
(1)
fland,
(2)
base load. and
(3)
automatic. In
hand
regula-
tion,
a fireman allends \0 a ballery
of
boilers and/or fur-
naces. He adjusts lhe valves and
da,rrp.:lrS
manually to
301
keep the pressure
ancVor
temperature
constant
In base-
load regulation, most
Of

a
gr~
of
boilers and/or furnaces
are cperated
at
a ste&'t,
hil1l
firing rare.
but
one or
fTIOfe
are operated at a variable rate \0 handle peak loads. In
71-97558-1
automatic
regulation,
an
automatic firing rale control sys-
tem ts used
to
provide
smoother reQ.Jlatlon
and
beUet
cOl'l'b.Jsl:lon.
Some
of
the
automatic systems used will
be

discussecUn this section.
AUTOMATIC FIRING RATE CONTROL
SYSTEMS
Different arranoemeF'lts
of
elements are used
10
pro-
vide firing rate control. Initially, the syStem
is
Iriggered by a
disturbaAce In the'CCintrolled variable, Such
as
steam
pres-
sure
in,aooiler
or
wall temperature In a furnace.
The
initial
disturbanca then causes a sequence
of
adjl lStJTlentS,
In
parallel
or
in
cascade (series), to control the various parts
of

the syslem.
For
exa~le,
in
a parallel system, a change in steam
pressure
may
cause simultaneous adjustment
of
fan
speed
and
'damper
opening
to
change the airflow,
and
pu~
speed
and
valve
opening
to
control the
flow
of
fu&:
(all).
In a cascade system. a change in steam pressure
might lnlllate a change In cCllTbuSlion airflow,

and
the
dlange
in airflow
might
lhen
adjust the rate
of
fuel
flow.
Funher cascading
might
occur
it the airflow
is
changed
by
an adjus1manl
of
Ihe
induced draft,
and
lhe
resulting
ct\aIlgEl in furnace pressure
is
then corrected by a change
in the forced draft.
A firing rate control
system usually falls

inlo
1
of
4
gen-
eral
classes-paranat,
serieas·fuel, sories-air,
or
calorime-
ter syStem. Each System
may
not
fall exactly Into 1
of
the
classes, but
l1'I8y
be
modified to
be
a combination
of
2
classes. Usually,
one
particular
syslem (or combination)
will
be the best

lor
a
panicular
plant based
on
economy,
type
01
fuel. safety required,
or
lhe
type
of
cperallon.
In
each system, a Change in the controlled variable
(such
as
sleam
pressure in a boiier plant
or
temperature in
a healing furnace) generates an error signal. The error
Sig-
nails
then
senT
10
adjust
the

fuel flow
and
air flow.
To
c0m-
pensate for varial.ions in fuel
condlion
or
lor
tube foUling
in
boilers. a ralio regulator (see
belOW)
is included lO-make
adjustmenls in
the
air-fuel ratio. The ralio regulator
maybe
as
Sirl1Jte
as the linkage between 2 valves,
it
may
be
a
valve-type device,
or
it
may
be a complex eleclrooic

device.
PARAl.l.El.
CONTROl.
SYSTEM (FIG. 1)
In the parallel control system, the error signal is sent si·
multaneously
to
adjust
both
fuetflow
and
airllow. The ratio
regulator may
~
in either circuil. It is generally
in
the cir-
cuit having
the
greater capacity,
so
the capaciTy
of
theboil·
er
or
furnace will not
be
reduced
if

the ratio
of
fuel
10
air is
decreased.
Thus,
ilthe
blower
or
fans have greater capac-
ily than tha fuel
feeding
equipment, the ratio regulator
is
pul in the
airflow
circuit.
The parallel syStem is
the
simplest
and
requires the
least hardWare. II is
nol
dependent
on
signals indicative
of
the actual

flOW
of
fuel
or
air. Therefore, it is most used in
plants where the fuel
buming
rate
would
be
difficult to
measure directry, such
as
a plant using grate firing
of
coal.
SEAlES-FUEl
CONTROL
SYSTEM
(FIG. 2)
In the series-fuel control system,
lhe
error signal con-
Imls
only the fuel
flOW.
Measurement
of
the fuel
flow

then
prcdJcBS a Signal that controls the airflow.
The
fuel flow
must
be readily measurable,
which
Is true
for
most gases.
liq,Jid fuels,
and
even pulverized coal. A series sysIem is
generally considered to
be
very effective in controlling the
air-fuel ratio because the
flow
of
one
is
used
10
determine
the flow requirement
of
the other.
Because
airflow
Is

the
dependenl
variable, air will not
Increase
if
fuel
is
not
available,
wen
t~
the SyStem
may
be
calling
for
more
heal.
This Is advantageous
00
equlJ:YT19nt
fired
wllh
a by-prcdJct fuel that
may
be in short
supply at limes. When lhere
is
a fuel shortage, the system
prevenls the InlrcducUoo

of
large quantities
of
air,
which
would deCrease
the
effectlve heat
El\l'9n
further.
However,
if
the air
SlWly
fails
or
airflOW'
Is reduced ex-
cessively by a fan failure, there is a danger
of
filling the fur-
nace with unburned fuel sinCe the error signal can still
cause the system to continue fuel flow,
Airflow
failure will
decrease the heat release in the furnace, further aggravat-
.I,!lg
the situation by causing a
demand
for

even mora
heat
and
fuel. Electronic circuits
may
be
used to overcome this
problem
by prOViding fuel cutback
If
eirflow
~g;
fuel flow
by a predelermined
amounl.
Also, a flame safeguard con-
trol can
be used
10
Shut clown the burner; the flame will go
OU!
when the air supply
drops
too
low
to
su~n
combus-
RATIO
REGULATOR

FUEL
FLOW
ERROR
SIGNAL

_.J_-,
I
ALTERNATE
I
'LOCATION
•
OF
RATIO
•
:
REGULATOR.
~
AIRFLOW
,

,
FIG.
1-PARAl.l.El.
CONTROl.
SYSTEM.
302
lion.
Many
burners
also

have airflow interlocks
10
shut
them
down
if
airllow decreases to a
predelermined
value.
SERIES-AIR
CONTROL
SYSTEM (FIG. 3)
"the Series·alr control system overcomes
thQ
disadvan-
taQ3
of
the series-fuel system; cutback
of
fuel is
lDb8rEl!J(
upon
a decrease In airflow. The
error
signal controls only
IhQ
airflow. Measuremenl
of
thQ
ail1low

then
produces a
sig~
that controls
the
fuel flow. Thus.
if
the airf/(lW fails,
the fuel
flow
will be decreased accordingly. preventing the
furnace
1rom
bEIIng
filled with
unburned
fuel.
This
system
is vel)' :satisfactory
and
IXlPUlar when fhe ail1low can be
readlly measured.
CALORIMETER
CONTROL SYSTEM (FIG. 4)
In
lhe
calorimeter control system, the error signal
CCll'l-
trolsoOnly

lhe
fuel flow, and measurement
of
the steam
now
produces
a signal thai
is
used
10
control ail1low, The
amount
01
steam
produced
is
proportional
to
the firing rale
(or
fuel flow).
so
fuel flow is measured indirectly
by
meas-
uring
steam flow. Because stearn flow is substituting for
fuel flow, the ratio regulator
is
in

the steam flow clrcuil.
It
lakes
a
definite
amount
ot
air to
burn
a quantity
of
a
given
fuel that will release a certain amount
01
heal. If the
rate
of
heat release
is
known, the
amount
of
air required
can
be determined.
The
amount
of
steam

prodJced
is pro-
p::>rtionalto the rate
of
heal release, so a measurement
of
steam flow can be used to control the airflow. Since a
measur<lment
at
steam flow
is
indirectly a measurement
at
heat, the system derives its name from
lhe
calorimeter, an
apparatus
for
mensurfng amounts
of
heat.
Steam leaVing
the
SuPerheater
is
usually held wilhin
close limits
of
pressure
and

temperature.
so
its enerlJll
content
per
p::>und
will
not
vary appreCiably. Therefore,
each
p::>und
of
steam carries the same
amount
of
heat
energy, so steam flow is
proportional
to the firing rate. It
steam pressure
or
temperature vary
el'lOUl;1l
10
causa
appreciable error, compensating devices can
be added to
the system to correct the
steam
flow

for
standard
conditions.
As with the series-fuel system. there is the danger
of
ac-
cumulating
unburned
fuel In the
furnace
if
the air
sowly
fails. A decrease in airllow will decrease the heat release,
which will deCrease
lhe
steam
!low,
causing a further re-
duction in airflow. Meantime, the
system
is
calUng for more
heat
and
more
and
more fuel is
being
&4JPlled.

As
in
thQ
series-fuel system.
eleclronic
circuits
may
be used to
OYElr-
come this
problem
by
prOViding fuel cutback; but in this
case, steam flow instead
of
fuel
flow
is
CClI'1l)3.red
with
airflow.
AIR-FUEL RATIO REGULATORS
Besides complex electronic systems (whiCh are be-
yond
the
scC9'3
of
this reference), there are 3 basic types
at
air-fuet ratio regulators -

Pl
area control.
(2)
pressure
control,
and
(3)
flow
control. All 3 actually keep the flow
rates
at
the
air
and
fuel
proponlonal.
They differ In the
ba-
sic prq:'l8rty that is controlled direCtly to achieve a
cO"lStanl
air-fuel ratio.
AREA
CONTROL (FIG.
5)
A simple mechanism is used to cause the opening area
of
2 valves,
one
controlling
airflow

anclone
controlling ruel
flow, to vary in
proponion
fa
each
other.
For 2 varves with
identical characteristics, a
mechanical
connection be-
tween them will produce
directly
proponional
rT'lO\IeITl9Ot.
If
one
valve rolates
through
a 45
degree
angle, the other
will also rolate through
a45
degree
angle:
and
If this move-
ment causes a 25 percent
chaf1Q8

in the flow rate
of
ona
fluid it will cause a 25
percent
change in the flow rate
of
ERROR
SIGNAL
I
AIJ'lfLOW
ERROR
SIGNAL
FUt:L
FLOW
RATIO
REGULATOR
AIRfLOW
I
RATIO
REGULATOR
I
".,
FIG.
2-SERIES-FUEL
CONTROL
SYSTEM.
303
I
fUEL

flOW
"

FIG.
3-SERIES-AIR
CONTROL
SYSTEM.
71-97558·1
ERROR
STEAM
SIGNAL
FLOW
I
RATIO
REGULATOR
,
FUEL
AIRFLOW
FLOW
"

FIG.
4-CALORlMETER
CONTROL
SYSTEM.
304
L
'
FIG.
5-TYPICAL

AIR-FUEL
RATIO
REGULATOR
USING
AREA
CONTROL.
(From
~srion
Handbook
by
North Amedcan
MfQ. Co., Qeveland, Ohio.)
1M
other.
If
the vatve characleristics are
not
the
same,
the
now
rales
of
the
air
and
fuel
will match
only
aI

one
lXlinl,
resulling In a lean mixture aI some
firing
rates and a rich
mixture at others.
Two·rotary valves
on
a
common
shaft
may
be
used,
but
a
~de
arrangement
with
a parallel
ann
or
Hype
lInkage Is preferred because the linkage
can
sometimes
be
adjl.lSted
to
correct

tor
different characleristics In
lhe
2
valves.
one
or, preferably,
both
valves should have
man-
ual
means
of
adji"lSling their
cpenings
for
setting the
air·
tueI
ratio Inilially.
The
L.9Cilream
pressurfil!S
01
both
air
and fuel must be
constant,
reqJlring
an

air
blower
with a constant pressure
characteristic
and
a fuel pressure regulalQ{ ahead
of
Ihe
fuel control valve. For all, ils temperalure must
be
con-
stanl fa avoid changaS
in
Its flow rate
0Je
10 viscosity
variali~.
PRESSURE CONTROL
(FIGS.
6
AND
7)
The resistance
to
flow
downsTream
trom
the clYltrol
valves Is a constant
in

boIh
the fuel
and
air lines
of
any
bum&l' system.
The
flow
through
a constant resistance is
prc:portlonaJ
(0
the &q.Jare
root
01
fhe pressure ditterentlat
across
lhal
resistance.
By
keeping the air and fuel pres-
sures equal (or proportional), their flow rates are kept
pro-
IXlrtional thrOU\1lOUI
lhe
entire turndown range
of
the
burner.

This
type
of
ratio regulator
works
with
constant ar·
eas
and
variable pr8SSUres,
which
is
lTlOre
accurate
and
usually less expensive
lhan
the area control msthod.
Wl1EIn
this
type
of
ratio regulator is in the fuel line,
il
is
cross-conneclad
10
the
air
Ii.ne

by
a small impul6B line,
and
vice versa. It c.onsi&ts
01
a globe-type valve in which Ihe
plug
is-aitached
to
and movecl
by
a diaphragm. 1'he pres-
sure
on
one
side
of
the
diaphragn
is proportional
to
that
01
the air line, and the prassure
on
the other side is
prC4'O'-
tional
to
lhat

Of
the fuel line. If the pressures are not the
same,
the urCialance causes the
diaphragm
to move.
The
diaphragn
mc:wes
the valve plug,
adjusllng
the flow
01
fuel
(01'
air
if
the regulalor Is
In
Ihe
air
nne) until the pressures
are the same.
The
air gas rallo regulator shown In Fig, 6
is
connecled
In the
gas
line.

An
air
I~lse
line
(usually
atxlul
'/4
InCh
pipe) Is conneclecl
10
the
CClfTPartment
below
ttlE!
dia-
phragm.
The
air pressure In the
i~16B
line Is adjl.lSteclto
achieve the desired alr gas ratio.
If the
maximum
air pres-
$Ute Is more than the maximum available
gas
pressure, a
tieed"f
is
used

to
permit a cenain amount
of
leakage1rom
the
1l"rpU16B
Une
10
ensure
tM
correci ratio at hiQh
firing
rates.
If
the
i~lse
line were left open
to
the almosphere,
111El
reguJalor
would
prOduce zero gas,
used
In
~ng
(zero governor) types
01
premixing
burners.

The
spring
is
used
for
counlerba.lancing the weights
of
lhe
shaft, plug.
and
diaphragn
assElITbly
so
that
the
diaphragm
1Joals
freely.
The
balancIng
diaphragn
prevents t.pStream
gas
pressure
acling
on
the underside
01
the valve
plug

from
lift-
ing
the plug.
When b.Jrning all In low-pressure air
atomizing
burners,
it
is
desirable
10
maintain
an
oil
pressure
several times
greater
than
lhe
COrTtx.lslion air pressure. The air-oil ralio
regulator shown
in
Fig. 7 prOduces a
oownslream
oil pres-
sure proportional
to
Ihe pressure elrertecl
on
the

tc:p
side
of
1M air diaphragm.
The
j~lse
air
pressure p lShes down
on the air
diaphragn,
lending
10
move
the valvs shaft
as-
serTt:lly downward.
The
downstream oil prassure pushes
up
on
the oil
diapnragn,
tending
10
raise the valve shaft
assembly.
The space between the diaphraQ'Tls is ventoo
to
the atmosphere.
If

the area
of
111EI
air
diaphragm
is 12
limes [he area
oflhe
oil diaphragm, the
oil
pressure has to'
be
12
limes
the air pressure in
order
to
balanc9 it.
The
oil
valve opens wider
untillhe
12:1 pressure ralio is attained.
An adjustable
lension
spring balanCes the weight
of
the
diap,ragms,
shaft

and
valve plug.
FLOW CONTROL (FIG. 8)
A llow control system actually measures Iheair1/aw
and
fuei
flaw
and
conlrols the flow
01
one
of
them accordingly.
A conslriction,
such
as
an orifice, is plaCed
in
both
the air
and fuel lines.
The pressure differential across the con,
striction
measures the flow thtough that line. Both pres'
~re
differentials are Iransmitled to some controliing
d9vJce that adjusts
Ihe
'low
0'

either the air
or
fuel to main-
tain the desired air-fuel ratio.
The
alr-gas
rallo
re(JJtalor shown
in
Fig. 8
conltols
the
flow
of
air. An Input coolrol valve controls the flow
at
gas.
upstream
and
downstream
Il'Jl=Iulses
from
an
orifice in the
gas line act
on
qJpOSite sides
oflhe
gas diaphragm. Simi-
larly', impulseS

from
the air line act
on
the
air
diaphragm so
as'to
oppose the action
on
lhe
gas diaphragm.
lhe
result-
ing
movement
of
the shaft between the 2 diaphragms is
amplified
and
transmitted hyc!raulically
(by
the hydraulic
,"
L'''(
+OAS
a"L"""""'"
O,

9>tR


"

'"'".:O"'-~:=:?:::§~
SPR,

",
Q.R''''''
FIG.
6-iYPICAL
AIR-GAS RATIO REGULATOR
USING
PRESSURE CONTROL, (From
Combustion Handbook
try
North American
Mfg.
Co.,
Cleveland, Ohio.)
relay and crank
type cylinder} to the butterfly valve in the
air line. The butterfly valve moves
untillhe
now (pressure
dif1erenlLal) across the air orifice balances out the flow
across the
gas orifice. The orifices are usually sized so
that equal pressure
drops
correspond to the correct ratio
01

flow rates.
The
ratio regulator also has a manual adjust·
ment
tor
selecting
the
desired air-fuel ratio.
,

FIG.
7-iYPICAL
AIR-OIL RATIO REGULATOR
USING PRESSURE CONTROL.
(From
Combustion Handbook
by
North American
Co., GJevs(and, Ohio.)
"R
ORIFICE
BUTTERFLY
VALVE
,
,
HYDRAULIC
RELAY:
RATIO
REGULATOR
I

~::PHRAGM'
.:.::1_:
MANUAL
RATIO
-
,
AOJUSTMENT
,
I
•
,
, ,
•
GAS
OIAPHRAGM
, ,
I
INPUT
CONTROL
VALVE
GAS I I U
"f, ;;GA;;;S: ~,,
~;;OR:;:';";;'C;;E"''':
+1,'
2 \
,
\
__
JJ
,


FIG.
a-TYPICAL
AIR·GAS
RATIO REGULATOR USING
FLOW
CONTROL. (From Combustion
Handbook
try
North Amen'can Mfg. Co., Oeveland, Ohio.)
305
71·97558-'
FIRING
RATE
SEaUENCES ~
TIle
size
and
aw1icalion
01
a burner
determines
how
II
iG
fired. Ditlerent
rnel!nds
01
flrino result In various
prepurge

configurations.
An
a,wrovall:lOC¥
may
require
a
specifiC prepurge COnfiq.Jtalion for a given awlica1ion.
The swilching required
fa
achieve a certain prepurge
corr
flq.Jralion is
providedby
the
proper
model
01
a flame sale-
guard
pr~ammlng
conlrol programmer).
METHOD
OF
FIRING
CONnNUOUS
FIRING
sinal1~t
burners,
such
as dtyQrs. are usuarty let! on

continuously. There
afe
also continuous InciJslrial fur-
naces
Ih~
which the work loads are conveyed
al
a
constanl
speed.
ON-OFF FIRING
TIle most economical method
of
firing is
sirrq::lly
to
turn
the
burner
on
when
heal
is
required
and
oft
when
there
is
er"lCJl 91

heat. This
is
the
most
efficient
method
because
the air-fuel ratio can
be
sel exactly at its optimum value,
an::!
it remains constant while
the
burner is on. Fewer con-
trols ars requlrec:l,
so
It is also less expansive initially.
Orr
01'1'
filing
is
used
mostly
on
warm
air
turnaces in residential
and corrmerclal buildings,
and
also for residential

awn-
aness such
as
hot
waler
healers.
HIGH-LOW FIRING

Hig Iow firing provid9s
.2
firing
rates,
high
fire and low
fite, according
to
"eat
demand.
The
high
fire rale is 00-
tained by simultaneously
PJs!tioning
lhe dampers
10
aO'nil
more
combustion air
and
the fuel valve

to
admit more fuel.
(In
a 2·slage
bur~r,
a
secord
fuell/alva
is
cpened
10
aO'nit
more fuel.l High·low
firing
is
used
on large, commerCial
and industrial
burners
to
provide a safe
Ii~t-off.
A higher
firing rare is r8QUired than
Is
safe for on-off firing,
so
the
burner must light off at
low

fire
to
al/Oid a possible
eKp1o-
sion. High
temperalure
blast turnaces,
such
as
brick
kilns.
use this
melhod
of
firing.
They
are
f~ed
as
high
as possible
for a short time,
and
then
turned
down
to
low fire
for
a

wnile. This
melhQj
has
been
found
10
save 10
to
15 per·
Cent
of
the fuel required
101
modulalac:l firing.
MODULATED
FIRING
Modulaled firing provides a gradually varying firing
rate. belween high fire
and
low
fire, according to heal
de-
marlCt The
burner
lights
off
at
low
tire. 1l1en a controller
varies

ll\EI
firing rate as necessary
to
k~
the conIrolled
variable (usually
prBSSUre
or temperalurel at the controllEi"
sel PJlnt.
Modulaled
firing
provides
precise coolrol,
but
it
is the least efficienl
because
it is
ditficull
10
keep the air-
fuel ratio conSlanl
over
the entire mlX1Jlating range. It is
used
on
industrial furnaces
or
bOilers
'or

applicatlOflS
re-
quiring
close pressure
or
temperature tolerances, such
as
chamical
process
heaters
used
tor tleal-trQ8ling metals.
306
PREPURGE CONFIGURATIONS
AJ:proval bodies require a
pr~rge
period, prior
10
oorner Iighl-otl,
to
remove
any
fuel or fuel vapors that may
have accumulated
In
th$
butner
or
stacks.
By

incrQ8sing
lhe
amounl
of
air
lTlOYed
through
the combustion
chafT',.
ber, the
possitillly
of
a rough
IiQtll-cN
or
explosion
clJa
10
accumulated fuel Is decreased. This is
why
a
~hlgh
fire"
prepurge
Is
usually required
tor
hi~-Iow
or
mcx)Jlalec!

methOOS
at
tiring. The
~high
fire" Is really a
l!!i~().I!I.!§Ir
since
lhere
is
ro
fire
during
prElPJrge.
What
it
really means
Is that the
darrper
controUing corrbustion air is c:penac:lto
lis maximum
~ition
to
move>
as
much
air as possIble
thrDU~
the combuslion chamber. This position is
thE!
same

as
the
high
lire
position
of
the
damper
during
the run
period
when
the
burner
Is firing.
It
would
seem
Ihal
the
longer
lhe prepurge
period
the
beller. However. a burnar system starts
~
when
there is a
call for
heat. Be10re the

burner
can
be
igniled
to
provide
heat, the prepurge
period
aclually
COOls
the system
OOwn
ev81'l
more. Therefore, [he beSt
pr~rQ8
coofiguratioo for
a gi"'en system is
one that provides sufficierll
airflow
in the
shortesllime,
taking
into consideration
~roval
00Cl'f
re-
quirements,
I~
01
equipmenl, and cost

01
conlrOls.
Prepurge types
and
firing rate
sWi~Chjng
necessary
10
meet
awroval
00Cl'f
req Jlrements for
vaiiOU'S
methods
of
flrinQ are summarized in
Table
I.
Insurance
comp9.r'1ies
in-
sure
bolh
prcperty
loss
due
to
explosions
and
dowr'1time

causing loss of productior'1. It
they requIre safely controls
thal causa
urnecessary
down
lime. they pay, Since they
reqUire cerlain firing rate contrOls,
you
can
see the imper·
tance
of
IheS4 controls
to
the safety
of
the Ourner system.
STANDARD
ON-OFF PREPURGE
No firing rate SwilCtling is
rElQJired.
The
amount
01
air
admiUed
during
the prepurge pariod is Itle same
as
the

amount
of
combuslion air provided
during
the run period
witr. the
burner
firing.
OPEN
DAMPER
PREPURGE
Firing
rale
swilChlne
in
fhe programmer
drives
a 2-posi-
lion
damper
molar
open
10
its
hi~
fire p.:lsiliOn near the
beginning
of
the prepurge periOd,
aUOW's

it
10
close
to
lis
low fire p.:lSihon before
ignition
trials, and drives il
back
open
10
high
fire
for
the run period.
LOW FIRE PREPURGE
This Is
!in
outdated
type
01
prepurge that is seldom
used anymore in flame safeguard
awlicalions.
Firing rate
switching
in
lhe
programmer
keEpS

a
proportioning
damp-
er
motor at ils
low
fire
position
until after i'7lillOn trials,
when switching releases the motor
10
modJlate
UI"lCeT
the
control
of
a series 90 pressure or temperature conlroller.
TABLE
I-PAEPURGE
CONFIGURAnONS
I
FIRING
RATE
SWITCHING

APPROVAL
POSITION
PREPURGE
APPLICABLE
METHOD

OF
BODY
CIRCUIT
TYPE
PROGRAMMERS
FIRING
REQUIREMENTS'1 PRE- IGNITION
RUN
REQUIRED
TRIALS
PURGE
PERIOD'
Standard R4140M
-
-
Nona
-
UL
On-Off
Ol"!-Off
On·Off R41S0A,M
UL
On-Off
Low
Open High High
several
R414OM's
1-wireb
High-Low
Dampe,

Fire
Fired Fire A4150Gl012,-G1079
UL
Modulating
(2-stage firing)
3-wireb
Low
R4127
Low
Low
FirSC
Modulate
or
4-wire Fire Fire
,
(Low tire prEipJrge) R4'SOH
R4126
Low-Hil)'l- 3-wireb
High
Low R4127Al1SS,·A1197
Modulale
UL Modulating
Moduiated
Lowd
or
4-wire Fire Fired A4140G
A41S0G
R4126A1172,-A1180,
·A1198
~and

Low·High-
3-wiraD
Low
High
A4140L
Modulate
I I (F.I.A.)
Low
or
4-wire Fires
Fired
A4150L
Provan
e
Modulating
R4181A1042,-A1059
&.
UL- Underwriters l at:x:lratories Inc. requirements.
<&"-Factory
Mutual requirements.
IAI-Industrial
Risk Insurers (formerly F.I.A.) requirements.
b Firing rate
motor
mUSI
close
by
itselt (spring-return) when power is removed.
C Outdated type; seldom used anymore.
d Low fire switch stops sequence before ignition trials until low fire position is proven.

ill Same
as
LQw·High-Low except additional high fire switch stops sequence near
begiMing
of
prepurge until hi1tl tire
p:lSil'ion is proven. '
I
Switching
returns firing rale motor to its low tire position when the run period is
OVer.
LOW-HIGH-LOW
PREPURGE
Firing rate swllchlng in
the
programmer drives a pro-
p:lrtioning
damper molar
o~n
to its
high
fire position near
the
beginning
of
the prepurge perioo,
closed
to its low fire
position
before Ignilion trials,

ard
releases
it
to modulate
under the control
at
a series
90
pressure
or
t9ITperature
controller
lor
the
run period. The programmer
has
provi-
sions for a
proved
10w-firl;l-5tart interlock
Oow
fire switch),
which stops
the
sequence before ignition trials until the
damper
motor
has
closed to its low fire position.
LOW-HIGH-LOW

PROVEN PREPURGE
This is the same
as
lOw-high-low prepurge, excepl that
Ihe
programmer
also has provisions for a proved high fire
interlock (high fIre switch), which slops the sequence near
the
beginning
of
the
prepurge perioo until the clarrper
m0-
tor
has
opened to Its hit;jl fire posillon.
PROVED
LOW-FIRE-START
INTERLOCK
A proved low-fire-start interlock Is r9QJired for
hl~-klw
Of
modulated burners (except those with low fire prepurge,
which is outdated and seldom
used
anymore). This inl9f-
tock must ensure that
allliring
rale controls are

In
the
low
fire position
(a firing rate no! eXCeeding 33 percenl
of
the
maximum) betote the burner can
be
iglited This is usually
accompllshed
by
means
at
an auxiliary switch
{low
fire
SWitCh)
mounted
on
the drive Shaft
or
the firing rale motor.
The auxiliary switCh is wired
inlo
the safety conlrol (pro-
grammer) circuit.
PROVED HIGH FIRE
INTERLOCK
In addition

10
a proved low-flrl;l-5tart interlock, Factory
Mutual and In:iJstrlal Risk Insurers (formerly F.l.A.) also
reQUire
a hit;jl fire swilch
10
prove thai the
~r
is tully
cpen
wring
prepurge
fo
ensure that
9I"lCll.Q1
air Is moved
!hrOU<tl the combustion charrber. The
hit;1'l
tire swllch Is
usually also an auxll1ary switch
on
the firing ratelOOlOf'.
307
71-97558-1
FIRING
RATE
SWITCHING
IN
PROGRAMMERS
By means

of
simpllfiod schematic dlagrams and timer
seq Jente
charts,
we
wlU
show how fhe
PfOlJfammers
ae-
CCllT'9liSh
firing
rate
switching.
For
simpliCity,
only
the cir·
cuits and conlaCts
nec~ry
10
de6Cribe
the
basic
operation
are
shown.
Fora
complete
description
ollhe

0p-
eration
cif
~
actual programmer, Jefer
10
the
Detailed
Orr
STaling
~nce
01
an
A4140G1007
(1orm
6D-0443)
or an
R4140L
"'-4"7
(form
60-{)4.44).
TImer contacts are oesicnaled M1B, M3A, etc. Termi·
nals L1
and
l2
are
the
-hoi-
and
~common·

terminals
01
ttle
power SLWly. External oevices are shown
in
001(95.
Operation
01
the firing rale motor Is deScribed in detail In
the
seedndpar1
of
this section covering Honeywell Control
Systems.
'
',WIRE
(OPEN
DAMPER)
FIRING RATE
SWITCHING
figs.
9 and 10
show
the
firing rala swilching of the
A414OM1020
and
A4140M1038
Programmers. Operation
o1lhe

lOY\'
fire provIng cjrcuil Is not shown because
II
is
similar
10
the operation tor 4·wire switching, which will be
d9scrlbed later.
A
2-posJl!on,
spting·t~um
llcluator is
used
to control
the dar'rper. When p:rNer is removed, a spring
en
the
ac-
hator
Shaft
m~chanicaJJy
returns
lhe
aclualor to its closed
position.
Prepurge starts
on
a cal!
for
heal.

As
saonas
properair-
"flow
is e!tab\ished,
Ihe
airtlow switch close's,
er'oergili~
','
the
damper actuator
on
terminal 10 (through the airflow
switch, jurrper, and M108).
TIle actuator drives
the
darrq>-
er open
~o
high lire
~ition).
At
30
seconds, M10B opens. The darrper actualor
is
d8-energiz.ed
an::!
the sprinQ-relurn drives Ihe darrper
clQSEld.
Al

~
~,
lnlern.al programmer switching
s:ops the timer until
the
low fire swilCh closes, proving thai
the daf1lJ9r is
in
ils low fire position before ignition trials.
Ignition lrlals begin
at
42 seconds. Tl1e darrper stays
closed during most
of
this period. Near lhe end
of
ignition
trials,
al
ti9.5 seconds,
M108
closes. The damp€lf actuator
Is
ergi.!:ed
and
drives Ihe damper open
(10
high fire
PJSi.
""~'UM&

&
Sli'I'TC>t
~~'-
TCll
" -
~
,CLOSES_lot
",o"~
"""l(,w
IS
In

l.SHII>I
1'.lJ
c_,

- ,'U>.TC
O
•
~
"1011&
0·10
~

&
~T""To
AM

,.
,~.

5"'

v
""'''
lOON
IUAC
S.CC""".
&
, A

,

T

,.UA"lICI.""ffN
U
'NAU"

O

A

IN
CA""~
ACTUATM
,S"IlC,
11
A
'·I'O:I'''''''._'''~·.I'''''N
AUU.HOII "


D
rocoorr"OL
tNE
c

-
~_.
-'

,'

6
::::'
" ,
,.
,,-a
~_
,,,_,,,
,

Ib "

_
D'.
"",-
'"'

'


,
""

""'
-
.d::,
,,<PI
"

_""-_,,~

.1:.
.~"
"
.,

_

"'''' '''''
""
0

,,"
,,,,,,,
FIG.
'0-
TYPICAL
TIMER
SEQUENCE
CHART

FOR
'-WIRE
(OPEN
DAMPER)
FIRING
RATE
SWITCHING.
tion) for
the
run period. The timer steps for
!he
run
periOd,
and
I'"
damper stays open during
the
run period.
When the tun period
ands,
the
limer
starts. The
caU
for
heat ends and power is remoVEldfrom terminal
10,
deener·
gillng
the

acll.la~or.
The
spring-return drives
tM
damper
closed.
3-WIRE
FIRING
RATE
SWITCHING.
Figs.
'1
and 12 show
the
firing rate
sWitchi~
at
old
type, 3-wire R4150L Programmers. Operation
01
the high
fire and
lOW
fire proving circuits is
nOI
shown because
it
is
similar to the opera.tion for 4-Wire switching, whiCh follows.
Notice lhat

the
prQgramrner SwiTching (Fig.
111
doeS
not
awly
power to lhe motor,
but
cnly shorts between molar
and c()l"(roller terminals,
or
opens them.
A proportioning,
sptfng-return
or
spring·biased motor
must
be
used to control the damper. When the red
·R~
(comrrn:n)
lag
of
the
circuli fa a spring·rerum motor
is
""S<r1.
'AOG

ME



n
co"TML
._-
".
,
-

,
0'
~
H'CH
.,

1
'0
• •
~
n
•
r
10
"OCU"AT~
It;
Lr.,
~.
L ;;.
=.~
~.,o,

0-,"
"

'NO
&.
.L"CON1.~TI
••
'
~"'""

"",OOY
I"OIm""
!n

o
-
FIG,
11-
TYPICAL
3-WIRE
FIRING
RATE
FIG
9-
TYPICAL
1-WIRE
(OPEN
DAMPER)
SWITCHING.
FIRING

RATE
SWITCHING,
308
. . .
n."

"< ",,,",",,,,
,

""'.
&

"",""
_""""'_
~
" """."

,._._

,

"

,,,

,0,,,

.,

,,,




,,""
"""
&.
~.~.:,~~~::::';",
~::::=::;"'.:,~:,
":,, ::'

""""",,

_ "
u"",
,.
FIG.
12-TYPICAl
TIMER
SEQUENCE CHART
FOR 3-WIRE FIRING RATE SWITCHING.
opened, a spring
on
the
molor
shaff mechanically returns
the
molor
10
its closed position. The spring·tiased molDl'
has a

spring
allached\o
ilsbalancing
relay. When the
"R"
leg is coened, the
spring
pulls the
balancing
rela.y
to its
closed position,
and
the
molor
is
than electrically returned
to ils
closed
posilion.
As
usual, prepurge starts
on
a call
for
heat. At 2 sec-
Or'lOs,
M98
closes, shorting between terminals 10
and'

1
on
lheprogrammer.
and
between terminals
Rand
B on the
firing rate molor. The
motor
dlives the
damper
cpen
10
its
high fire posi\ion.
At
7 seconds. internal
prCJgrammer
switching
stops
lhe
timer
unlillhe
high fire switch closes,
prOVing that the
damper
is
open
10
provide maximum air·

flow during prepurge.
At 42 secondS, M9B opens,
opening
Ihe
•
R·
leg
of
the
motor
circuit. The spring (or spring-bias) drives the motor
and
darnpel' closed. At 60 seconds, internal prCJgrammer
switching stops the timer until the
lOW
fire switch closes,
proving
that the
damper
is in its
low
fire position before ig-
nition
trials.
Ignition trials
begin
at
72
seConds,
and

the damper
stays closed
during
mas!
of
this period. Near
Ihe
end
01
ig-
nition
trials, at
101
seconds, M9A closes, shorting be
t

een
terminals
11
ard
12
on
Ihe
programmer, and
connecting
the A terminals
of
the
molar
ar.d controller.

The firing rate
motor
is released to
mcx:::Iulate
under
conlrol
of
the series 90 coni roller. The limer slops for
Ihe
run
period.
The firing
rale
motor
modulates
according
10
heat de-
mand
during
lhe
run period. When the run period
endS,
the timer slarts. Al 118 seconds, M9A opens, cpening the
•
A·
leg
01
the
malar

circuit. The spring (or spring-bias)
drives the
molar
and
damper closed.
4-WIRE
FIRING
RATE
SWITCHING
The 3-wire firing
rale
switching Circuit restricts
users
~o
a firing rate
molar

ith a spring-return
or
spring-biasecl
balanCing relay. Therefore. newer A4150G
ard
Lmcdels,
and
all A4140G
and
L models, have 4-wire firing rate
switching circuits. These
models
also

allow
Ihe
use
of
m0-
tors thai are
electrica.11y
driven
in
both
directions.
FiQS.
13,
14,
and
15 show the
firing
rale
switching
01
a
typical R4140L Programmer. Operation
01
both
the
higl
fire
and
low
fire proving circuits Is shown (Fig. 14). R4140G

I'T'ICX1els
have provisions
only
for
the
low
11re
switch.
Prepurge starts normally
on
a
call
10r heal.
lhe
timer
motDl"
(Fig.
14)
Is energiZed IhroU(1l MJA.
Al
3 seconds,
M10B
opens
ard
Ml0A
closes (Fig. 13),
shorting
between
terminals 10
and

11
on
the
programmer,
and
between
ler·
minals
Rand
B
on
lhe
1iring rate motor. The motor drives
lhe
oamper open to its
high
tire position. At 10 secondS,
M3A opens (Fig. 14), stc:«>ing
the
timer molar. When
the
high tire switch closes, prOVing
thallh8
damper
Is cpen
10
provide
maximum
airtlow
during

prepurge, the timer motor
is energiZed
thrOUQh
tha
high
fire $Wilch
ard
M5B;
prspurga continues.
At 20 secondS, M3B closes (Fig. 14), bypassing the
high fire switch. At 26 seconds, M10A
opens
(Fig.
13).
cpening the A leg
01
Ihe
motor
circuit. If a spring-return
or
spring-biased
molar
is
used,
it
starts
to drive the damper

,


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IZ
••
O
SECONO"_
FIG.
13-
T'(PICAL
4-WIRE

FIRING RATE
SWITCHING.
u

~~-

"
'0" "
••
;WITCH
11
AU
CON'ACTS

,
""""'NI~
'Hl
nA~C'."
!'()$fT'''''lu~o
"CO~OSI
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""TC~
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'0
11
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"38
C_>O
Q


FIG.
14-
T'(PICAL
OPERATION OF HIGH FIRE
AND
LOW FIRE PROVING CiRCUITS.
309
71-97558·1
'
00-
_
f!:"

_
"
.:.

f!:" _

- -
d>.=.
__

_".,_

",.
&:,._
_-,-"


_

&"
_



,._ '_
~

.
,.
"
"-,.,,

_

.
_,
",, ,.

-

- -
FIG.
15-
TYPICAL
TIMER
SEQUENCE CHART FOR
4.WIRE FIRING RATE SWITCHING.

closed.
At 30 seconds, M10S closes, shorting between
(ermlnals
l'
and
14
on the programmer
~hrough
M10S
and
MBS).
and
between terminals
Rand
W on lhe firing
rate motor. If an electrically
driven motor is used. il drives
the damper closed Al
5'
seCOl'lds.
M5B opens
(Fig.
14),
st,,",lng
the timer motor.
MSA
closes. When the low fire
swllch closes. proving
(hat the damper
Is

in its low fire
IX>"
slim
before Ignition Irials, lhe limer molor is energized
(hrou~
lhe
row
tire switch
and
MSA;
prepurge continues.
Of
the low fire switch
is
connecled in the alternate Iocallon.
the limer
molar
16
energizecJ through M3B, the low tire
switch. and
M5A.)
Ignilion trials begin
al
60
seCO'ldS.
and
the damper
slays
closed during
most

of
this period.
Al
66
seconds.
M3B
opens and M3A closes (Fig.
14),
bypassing oolh Ihe
high fire
and low fire
swilCheS.
The timer motor
keeps
run-
nil1Q
and Ignilion trials continue, Near the and of ignition
trials,
al95
seconds, M8Bopens
and
M8A closes
(Fig.
13),
shortinQ belween lerminall!l"
and
120n
the programmer
(through
M1

OB
and
MBA),
and
conneCllng the R terminals
of
the motor and controller. The firing rale molar
Is
re-
leased
to
l1"lCllislale
under control
at
the sefles 90 control-
ler. The limer
st~
for Ihe run period.
The firing rale molar modulates according
10 heal de-
mand during
lhe
run period, When Ihe
run
period
ends,
the
limer statts. AI
'12
seconds, MaA opens (Fig.

13),
openll1Q
lhe R leg o1lhe malar circuil.
11
a sprinQ'relurn
or
sprinQ"biased molar is used,
Il
starts
10
drive the damper
closed.
At
'16
seconds,
MBS
closes, shorting be/ween
terminals
l'
and
14
on Ihe programmer (through
"-1108
and
MBSl.
and between lerminals
Rand
W 01
lhe
firing

rale motor. If an electrically driven molar is usecI. il drives
the
damper closed.
310
PART
II-HONEYWELL
CONTROL
SYSTEMS
HONEYWELL
CONTROL
SERIES
The electrical
series
of
a
control-20,
40,
SO,
60,
70,
80,
SO-identifies the vqllage leve! on which a conlrol ~r
ales
and
Ihe
switching
or modQ
of
operation
it

provideS.
Cqnlrollers
provide
spst
or
SIXft
swilching, and switch
eilher line
or
low
v01laga. (For further information on con-
trolla'rs, refer
10
Ihe
Flame
safeguard
Reference
on
Auxil·
lary Equipment, form 70-8120.) We can
see
that
by
combining
Ihese 2 factors,
we
can identify 4 dil1erent
S&
rias
-spsf

line,
spst
low,
SIX1I
fine,
stXfI
[ow. These 4 series
and their characteristic controller switching actions Bfa
-sho'wn in
FiQ.
16.
SUUES
_0
SERIES
ZQ
LINE
'0"0
l TAGE·SI'll
lOW
VOt
UOt·UODT
o 1
g-'r
SE",n
IilI
LI
NE
VOlT
AGE
.sPOT

ftMIEUQ
lOW
VOL
TlCE.sP:IT
URIES
!ilI-MECMAM'CAl $(RIES
7Q-fUCTROlilt
U"I~S
llI-liKlOULATI/lC
FIG.
16-HONEYWELl
CO~TROL
SERIES.
Series 20 (low voltage,
spjI)
is
not
USEId
in flame
safe-
guard
applications.
series
50
(mechanical)
is
represented
by
V50S5
and

V51
E
gas
valves,
which
have separa:e ac-
tuators,
and
by
the VS060A Supervisory Fuel Cock. Series
70 (electronic) Is represented
by
name detectors
and
flame signal amplifiers. Series
80
~ow
voltage.
SPSI)
is
rep-
resented
by
a few
flame
sa1eQ.Jard
primary Controls
(RA890'S) indicaling simply
thai
they have a low voltage

contro
circuit.
and
by
a
tew
SQlenoid-opllrated gas valves.
Series
40
and
60 (line voltage),
used
in
on-otf
or
hiQ1·low
Systems, will
be
discussed briefly. Series 90
(mociJ~ting\
is the hearl
at
mosl
firing
rale
control systems, so it will
be
described in detail.
Table
II

summarizes Honeywell control
series.
SERIES
40
(LINE
VOLTAGE,
SPST)
CONTROLS
CONTRO~LERS
AND LIMITS
Series 40 controllers
ard
limits used in flame saf9QJS.rd
awlications
are
commonly
temperature or pressure sens-
Ing devices.
They
provide
::.pst
(singla-pole, single-throw)
swaching. In
olher
words, they make a set
at
contacts
to
start
SyStem

operption,
and
break the
sel
of
contacts
10
stop'
SyStem
operation. .
Se(ies
40
controll(Jrs
and
limits
are
rated
for
direct
switching
of line voltage loads. They commonly
use
either
mercury switch
or
open contact switChing mechanisms.
Open
contact mechanisms must
be
snap-acling 10 pre-

vent
arcing
across the contacts.
FINAL
CONTROL
ELEMENTS
series
40
final conlrol elements - solenoid valves,
re-
lays, contactors,
and
motors-
have only 2 positionS. They
remain In the normally de-energized position
until pow·
ered; at which time,
they
g)
10
Ihe energized position,
When
pOwer is Interrupted, they return
autanallcally
10
the de-energized position. A
normally
closed series 4()
solenOid valve,
ror

e)llample,
opens
when
powered,
re-
mains open
as
long
as
power
Is
aw1ied.
ard
closes as
soon
as
power
is cut off.
311
Fig, 17
shows
a series 4() relay.
CC{11roJ!ed
by
a series
40 cootroller with a series 40 limit.
TIle
relay
shown
pro-

vides spst switching; it
could
provide more
COf1'l>lex
switching control,
The
S91les
desiglalioo,
series
40.
re1ets
10 the control circuit
voltage
ard
control Circuit switching
action.
If
the sWitching action
01
the relay
shown
were
spdt,
the relay
would
no!
be
desiQr1aled
serles
&l.

eYen
tl10uQh
it provides line VOltage spdt: swilching, It
wwld
re-
main
series 40 after the
Coil
circuit.
TIlere are, in fact,
no
series 60 relays
and
no
series
60
soJ9I"lOld
valves.
since
lhese
devices are,
by
nature, on-off (spst) controls.
SERIES 40 MOTORS
series
40 motors
are
atso 2
position
devices.

TIlernolor
drives open wtlen powered, remains In
the
full
opal
posi-
lion
as
long
as power
Is
applied.
and
then
returns aulO-
matically
to
the clOsed
posillon
(by spring
force)
when
de-energized. Fig. 18 shOws a series 4()
motor
under
cen-
Irol
01
a series 40 controller.
The

limit switch
cuts
off
power
to
the
motOl'
windirv;>
When
the
motor
reaches
ils
full
open
po:sillon.
The
braJlfI
'rVinding
holds
the
armature
agaInst a brake
shoe
10
hold
71·97558-1
TABLE
/I-SUMMARY
OF

HONEYWEll.
CONTROL SERIES
SERtF.S -
DESIGNATION
CONTROLLER
TYPE
CONTROLLER
ACTION
RELAY
OR
VALVE TYPE
MOTOR
ACTION
Series
20
3-wire.
bw
valIaOS'
12~illon,
spd:)
c
Makes clrcui:
to
stan;
makes second circuit
10
stop.
-
low
voltage: folates 180·

10
open,
cCYItfnues
180·
10
close; stops
on
p::lw&r
intefruptio,,,,
-
Series
40
d
2·wire.
'ine
Voll8Qe
(2-poSitlort spst)
Makes circuit
10
start:
breaks
Itto
stop.
Line voltage coil
circuit; makes
(opens) when
pcM'8red;
breaks
(cICJSBS)
wilen

power's inler-
rupled.
Una
voltage: motor drives
open

hen
po

ered;
spring
returns clOsed
on
r;.ower
Interr~uon.
Series
SO
Mechanical (nonelectricalJ series.
$erles60
3-wir&, line- voHage
(2-position,
spjtj
Makes
circuilto
stalt;
makes second circu,t
10 stop.
-
Old style
-line

vOltage
equivalent
of
series
20.
New
style-line
Of
low
voltage drives
qJ9n
when
powered cpen; reverses
and
drives closed when
i
p:lWe~ed
closect, stops
on
p::rwer
interruption.
Ser;es
70
Eleellonic
series.
Series 80
2-wire. low voltage
(2-posilion.
spst)
Makes circuit to start;

breaks
it to step.
low
voltage coil
tircuil;
mak:es
(cpensJ when
powered: breaks
(cIOS$s)
when
power's inter·
rupted.
Low yoltage; motor drives
operI
when powered;
sprJl'lg'relurnS closed
on
power Interruption.
Series
90
3-wire, low vollage
lmcdulalil)\i)
Varies rasislance
between
common
terminal
arx:l
2
erx:l
tarminals in response

10
controlled
vari~le.
-
Low
volt3ge; motor
modulates p:)Silion
in
response
to
changes in
con/rolled
variable
signaled
by
controller.
-
FIG.
17-TYPltAL
SERIES
40
CONTROL CIRCUIT.
SU\lEUG
SlAtES
e
ClI11TAOlltA
uer
lJlf
VOLTAGE
I'll.EII

!UrPL
V
SUIlU"
I!HAV
"
C4IlfrACLl(CI
(QUI_IT
!he
""otor
cpe'1 after the limil opens. When both motor and
brake wir.dings are eneroized, the strength
of
the
motor
winding
overcornElS
the brake winding.
The sequence
Of
operalion
01
the series
40
l'TXltor
is
as
tolloW5:
1. The conlroHar contacts
crose.
2. The mo(or

windings
are energized; brake winding
is
overcome and the moIor drives cpen. (The riQht harx:l
winding
is
energized directly; the
\e1l
nand
windillQ is anar·
Ijlized thlough
a capacitor, SO fields are
OUI-of-phase )
3.
The
motor
drives open (usually 90
or
160 degee:sl:
Iimil switch opens; brake windlnQ holds
motor
open.
4. The controller
contact~
open;
brake
windil1Q Is de-
enelgized;
an
internal sprinQ drives the

molar
back to
lis
closed p::lSltion,
Series 40
motors
are t50C/lo
power
both datT.Pels and
valves. In
lhe
most common applicalion, Ihe rootor
is
ap-
plied
to
drive
the
ce:t'llroJIed
valva
or
darrper
to
the
tun
312
-
-
1"'fU"
~O.TRlIl\l~

-
II
(11011
SEAlfS.
lIUTOft
SPRING
IIITURN
_
FIG.
18-SERIES
40 MOTOR CONTROLLED
BY
A SERIES
40
CQNTROl.lER.
open
position
whenever
the
molor
is
powered.
Nole
lha!
in
the
event
of
a power failure, the controlled
eQUipment

would
automatically
return
10
Ihe
closed
position.
This
lea-
ture is sometimes rEiferred
10
as fail-sa1e,
but
this notation
should
not
be
used
since il
implies
more
than
the
fact that
Ihe
molor
simply
closes
on
p:lwer

failure.
TYPICAL
SERIES 40 CIRCUITS
A typical series 40 control circuit, wilh a
hiQh
limit, is
shown
in
Fig.
19. The
controller
switches
power
to the sa-
I~NU
00
.COITRIlLL!:.
$PRllIlO
RETURN
FIG.
19-
TYPICAL SERIES
40
CIRCUIT WITH A
HIGH LIMIT.
ries 40
molar
or
valve,
or

other
line
voltage
load, directly.
If
Ihe load
were
10
exceed
the
rating
of
Ihe
controller
eM-
lacts, an intermediate
switching
device
would
be
used
be-
tween
the
controller
and
the load.
A
high
limit,

added
In sen'es
10
break
the
hotUne
to
the
controlled
eQUipment,
will
turn
off
the
motor
11
the
c0n-
trolled variable (pressure or temperature) exceeds
Us
preset value. In
some
Sf:PJications, a reverse-acting limit
connected
In
The
sarna way as
the
high
limit

might
beused.
A reverse-acting rimlt Is
one
tnat
breaks
a set
of
contacts
on a
drop
in
the
sensed
condlllon
rather
than
on a rise.
115
function
would
be
10
prevent
system
operallons
unW cer·
taln
conditions
are attained. In a

steam
heater, 10r exam-
ple,
a reverse-acting
limit
might
be
Sf:Plied
10
prev~t
the
circulation
01
cold
air
by hording
up
molor
operation
until
steam
pressure has risen
to
the
limit
setting.
A
low
limit
would

be
connected
In
parallel
with
the
con-
trol:'er, as
shown
In Fig. 20.
If
Ihe
controlled
variable falls
below
a preset value, the
low
limit
contacts
close
and
start
the
molor.
Thus, tile low limit
maintains
a
given
minimum
condition

by
operating
the
controlled
equipment
as neces·
sary, even
when
the
controller is
not
calling
for
heal.
SERIESOI
lU-
LIIlIT
IINfI

"Tao
Ll
I$Tl
U
SPRING
RETURN
.~"
1~l'Pll
-
FIG.
20-

TYPICAL
Se,RIES
40
CIRCUIT
WITH
A
LOW
LIMIT.
313
71-97558-1
SERIES
60
(LINE
VOLTAGE,
SPOT)
CONTROLS
CONTROLLERS AND LIMITS
series
60 controllers
and
limits
are
line voltage, 3-wire,
2-p::E.iliOl"l.
spdI (single-pole,
doUble-thrOW)
controllers. A
series 60 conlrolieT
or
limit breaks

one
sel
01
conlacls and
makes a sec::ond6Etj,on a rise in
the sensed condition, and
also on a tall in
the
sensed condilion. For example,
lhasa.
rie$ 60 19rrper8lure conlroJisr
shown
in
FI(;l.
21
breaks
the
sel
01
contacts
between
terminals
A
and
IN
on a
mop
in
larrperalure.
It

simullaneously makes the sal
Of
contacts
,between terminals A
and
B.
,
co_o_
~
,
ll.UES
A·I
ON
Tnl~.
'ALL
=
L-@-
MAlES
R'"
OM
n

RISE
-
FIG.
21-TYPICAL
SERIES
SO
CONTROLLER.
Series

60
controller!;
and
limits
can
be
used
loperlO1m
the function
01
series
40
contrds
by
uSing only half the
switching available, as
shown
in
FiQ.
22.
The remaining
SYfilcninQ capability
may
be. used 10 perform some
acX:ll-
lienal function.
FINAL CONTROL ELEMENTS
series
60
final control elements are motors only:

501&-
noid type controls (valves, relays,
and
cOll1actorsj ara,
by
natura, series 40 spst (on-off) controls.
.lIln"C~"-1II0llU.
U~liS.UMIT
""fOIl

lllO
fUll'llOIl
'UFORIIlIlC;
FUIICT'OIi
DF
lUlU
~1I0llU
llFSERIU4tlUll1lT
®
•
COUIIDLlIO
EOUIPMUT
.(i)
.(i)
'i'
I
<D
-,
:::
-,

'
-
FIG.
22-USING
SERIES 60 CONTROLLERS AND
LIMITS
IN
PLACE
OF
SERIES 40.
314
SERIES 60 MOTORS
Old
slyle series 60
motors
ware simply the line voltage
eqUivalent
of
series 20 motors.
T1">ey
rotate only in one di-
rection-turning
through
180
degrees
10
the
c:pen
posi-
tion.

and
Continuing in the same
direction
through
another
180 degrees
to
the closed p::lSition. ReCently,
this
type
01
MOtor
has
been replaced
by
a new style series
60
'iIOtor.
The
new style motor is avaIlable in line
or
low voltage
models. I! is reversible; the
molor
drives
either
90
or
160
degrees in

one
direction,
and
drives closed in
lhe
~lle
direction,
A diagram
01
the new style series-60
molar
is snown in
FiQ.
23.
W"'Ien the controller
makes
R
to
W
as
shown, the
riQht-hand
molar
windirlQ Is enerQized direclly
and
1he
lefl-
hand wind;nQ is energized
lhroogh
a capacitor

10
drive the
motor
to
one
end
01
its stroke,
where
il
is
sto;::ped
by
the
,otalional limi! swltcn.
-~I=~:;)-l
SERln
ill
i CO.TRDllER
"
"
POWER
RETURN
."",
IU""LY
FIG.
23-
SERIES 60 MOTOR CONTROLLEO
BY
A SERIES 60 CONTROLLER.

When
the controller
makes
A
to
e,
the lefl-hand
wiJ"'ldo
ing Is powered directly, and the right-hand winclirlQ
through
the capacitor.
The
motor starts
and
drives
10
the
other
end
of
ilS
slrOke, where it is stopped
by
the limit
SWitCh.
Series
60
mrn01S
do
I'lOl !slurn

10
the
Closed pas)tiOn
i'
power
10
the motor Is
intern pted-inSlead,
the moIor
re-
mains
In
whatever
posillon
II
is in
when
p:Jwer
is
cut off.
For
this
rea5On, series 60 motors
are
not
used
where
it
Is
necessary Iha11he valve

or
damper
being
conlrolled close
on
power outage.
•
•
•
••
SERIES
90
(MODULATING)
CONTROLS
series
90
controls
are
commonly
used
in 1lame safe-
guard
systems
to
provide
modulating
control
01
a
burner's

firil"lQ
rale.
In
2-lXlsi\ion
conlrol
systems. a final control ele-
ment,
once
BQsrgizad, is
limited
in lIs
q:leration
by the con-
trcillar
and
the limit
switches
in the molor. It must run
toone
of
its
'2 B:<lreme
positions
and
remain there until
condilions
at the
controller
have changed
through

the
enlire
range
of
ils differential. In modulating control systems, the cOntrol
molor,
when
energized,
runs
only
90Clt1Qh
to
move
the
Ii·
nal
control
element a
dislMeB
prc:portional
10
the change
in'the
controlled
variable. Thus, a
modulating
conlroller
is
able
to

position a modulating motor
at
any position trom
fully
cpan
(high fire)
10
fully
closed
(low lire).
SERIES
90
(MODULATING)
CONTROLLERS
A series 90,
or
modulating. controller c:bes
nol
contain
a Switching meChanism;
bul
instead contains a variable
re-
sistor.
or
potentiometer
(Fig. 24).
The
modulating
control-

w
POTE~T10METER
SCHEMATIC
FIG.
24-SERIES
90
(MODULATING)
CONTROLLER.
ler
potentiometer
typically consists
of
fine
wire
wound
around
a core; a
wiper
rests
on
lhe
wtndings
and
can
move
alol1Q
them.
The wire
ends
are

connected
10
terminals labeled W
and
B.
The
Wiper is
connected
to terminai
A.
As
lhe
wiper
moves
back
and
forth,
the
amount
of
resistance between
A
and
W
and
between
A
and
B changes.
If

the Wiper
moves
toward
W, resistance Increases
between
A
and
B
and
decreases
between
R
and
W.
A series 90 (modulating)
controller
is
shown
schemati-
cally
in Fig. 24. The A, W,
and
B
designations
stand
10r
red,
while,
and
blue

leadwire corors.
Typical
modulating
controllers
used
in
name
sa1eguard
appUcations
sense
temperature
or
pressure
corditlons.
The
wiper, R, moves
toward
W
on
temperature
or
pressure
rise.
The
wiper,
A,
moves
toward
B
on

temperature or
pressure
fall,
Since
the
wiper moves 1rom
red
to
btue
on
a
315
drop
in temperature, indicating a
need
for heat,
ltle
lollow-
ing
memory
device is
onen
used:
~RED
TO BLUE FOA
BTU.·
The
modulating
controller
q:l8rates

within
a cartain
range-cailed
the
proPJl1ioning range (or throttfingrangej.
The
set poinr
of
the controller is
usually
in
the
center
of
the
prop::lrtioning range,
al1hoUQh
it
is at the
low
end
01
the
range
on
many
conlrollers.
t-
PIIOI'QIIT'QNINc;
A"'Nc;~

1
I
1~PI5.'CI
sn
POINT
I I I I I t I I I I I I
"P
1~f
1!if
[1'.JCI
UUCI
[23.'CI
FIG.
25-
PROPORTIONING
RANGE
OF A SERIES
90
CONTROLLER.
With
a prc:portioning range
of
10 F [5.6
Cl
and
the set
point
at 70 F [21.1 Cj as
shown
in

Fig. 25, the controller
wiper
can
move
from
one
end
01
its
range
at 65 F [18.3 Cj
to
the
other
end
at
75 F [23.9
Cl.
In
other
words, R·B resis-
tance
will
be
zero
at
65 F [18.3 Cj,
and
R·W will
be

zero at
75 F [23.9
Cj.
In a
heating
system,
the
controller would
cause
the
modulating
motor
to
run
all
the
way
c:per1
al65
F
[18.3
CJ
and
allihe
way closed
at
75 F [23.9
C/.
In
between

these
points,
the
motor
position
will
be
prcportional to ttle
temperature
within
the
prcportloning
range.
SERIES
90
(MODULATING) MOTORS
A series 90 Controller is
connected
to
a S(jries 90,
or
rooc1Jlating,
molar
as
shown
In
Fig.
26. A series 90
molar
operales

on
low
\/Oltage,
so
a
transformer
is rEQJired The
motor
also contains a
solid
state
balancing
relay and a
feecback potentiometer.
The
solid stare balancing relay
funclions
liKe it
has
a
center-plvoted armature
with
a
movable
c.antaC(
between
two
fixed
contacts.
When

current
flow
thrOl.(tl
one coil
ew-
ceeds that
thrOl.(tllhe
olher,
the
armature
tlIts, causi:'lQ
the movable c.anlacl
to
touch
one
of
the
fixed
contacts.
The
center (movable}
coniact
c:bes
nol
louch
either fiwed
contact
when
EQJal current Is
11owil1Q

in
both coils G)
and
<V
Some
motors (like
the
M941)
have
a
spring-t:iased~
balancing relay.
When
there
IS
no
current
nowlng
in either
coil,
the center
contact
moves
over
10
the
~closed·
c0n-
tact,
and

the
motor
dflves
closed.
ThUS the
motor
will
drive
closed
whenever
the
R
leg
of
the
circuit Is
~
The balanCing relay Is
normally
buill
within
the
molOl'.
However,
some
older
motars
are
built
withOUt an inlegral

11-97558-1
SlR1ESliO
CONTROLLER

,-
("
FIG.
26-SERIES
90
(MODULATING) MOTOR.
balancing relay so they
can
be
used
in an environment 01
e

lreme vibrations.
An
extemal
balancinQ relay is
used
with
lhese
molors, II
can
be remolely mc:onted
10
avoid
the

extreme vibrations
10
whIch
the
motor
itsell
might
be
sub-
.ieCled.
This is ro longer necessary
with
solid
state balanc·
il"lQ
relays. (The R927C Balancil"Q Relay is available
for
use
with
the M944B,E,J,R and M945B,C,G,Y
molars;
the
R9107A
is
for
use
with
the
M941B
molar.)

The
motor;lseft (Fig. 27)
Is
a low vollaga. reversible me-
lor.
Rotational
limit
switches stop the
motor
w~en
it
rsaches
ils fully opened
or
fully closed position.
The
direc·
tien
at
motor rotation
depends
on
which
molor
winding is
energh:e::I directly.
When
1.''1e
·openil'lQ'~
winding

is
ener-
giled
directly (balancing
lelay
contaci
louc"ling
contact
@ in !he figJre),
lhe
·Closing"
winding
'IS
energized
lhrough
lhe
capacHor
and
the
molor
ctlves
cpan.
The
feedback potentiometer
(Fig.
28)
in Ihe
motor
is a
Ihick 1ilm variable resistor

-similar
(n
Metion
to
thai in the
controller.
The
wipe(is
physicallY,conneCled
10
the motor
Shan, Any movement
at
ll)e
motor shaft causes
the
elecH!·
SERLES
to
CON'
#tOLeE"
SERIES
90
MOTOR
,

-
FIG.
27-
THE

SERIES
gO
MOTOR.
cal resislal'laJ
be/ween
the wiper
and
either
end
of the
p0-
tentiometer 10 Change.
The
operation
o1the
motorwhelher
it
drivesOj)en,
closed,
or
is
sl~-dependson
theposi·
lion
of
the
balancing
relay.
"'OTO~
~~AfT

FEEDBACK
POTENTIOMETER
RIS'STANC!
,,'NJ;>'''on
R
S£"'U;lIO
C'JNTROLlrR
•
FIG.
28-FEED
BACK
POTENTIOMETER
IN
A
SERIES
90
MOTOR.
BASIC OPERATION
OF
A SERIES
90
CONTROL CIRCUIT
The
IXIsitbn
011he
balancing
rEllay
is CIBpenOenI
on
tile

amount
of
current
going
through
the
relay coils. Whenever
:urrent
flow
In
ttle
coils
is
uneqJal,
lhe
balancII"lQ relay will
conlact
one
01
the
21ix9d
contacts
anctlhe
motor
will run.
Whenever
currenlllow
Is equal,
Ihe
balancing

relay will as·
sume a centered
~ition,
and
[he
molor
will
not run.
Cu~renl
flow in
Ihe
balancing
relay coils is
dependent
on
the resistance in each motor.conlroUer
"leg,·
of
WllCtl
lhebalancing
relay
is
a part. The conlroHer and
motor
10rm
2 separate
legs
(Fig.
29)-the
W leg Jnclude5

!he
left side
olthe
controller IXIlenliometer coif
CD,
and
lhe
len
SIdE!
of
,
•
•
LEG
'"
\
~
R
R
,.
"'

•
~
COIL
-n
n:-
COIL
i
\

"!
q
l)l:
.g
7.·
~
~~,u
m.
-
FIG.
29-TJ-lE
2
"LEGS"
OF A SERIES
gO
CONTAOl
CiRCUIT.
316
the
motor
feect:lack potentiometer. The B leg includeS the
right side
of
the controller potentlomeler, call
<V
,
and
the
right side
of

the motor feed:lack potentiometer.
Under conditions
of
9QJUlbrium (Fig. 30), the
total
resis·
tance
fn
the W leg equals the
toral
resistance
In
the B leg,
so the current flow through coil
CD
eq.Jals the current flow
through coil
<V.
The balancing relay coils, transformer
secondary,
and
wiring are
all
cooslant resistances.
R1,
A2,
RJ,
and
A4
arfi

variable reslslances. When the le;)S
are-
balanced, B1
plus
A3 eq.Jals A2 plus
A4.
FIG.
30-
SERIES
90
CONTROL CIRCUIT WITH
THE LEGS
BALANCED.
Assume Ihat the controller is a temperalure
SBIlSing
de-
vice.
On
a drop in temperature at
the
controller (Fig. 31):
1.
The wiper on lhe Controller moves toward the B
terminal.
2. Resistance A2 decreases and
R1
Increases.
3. The total resistance
01
the B (blue) leg decreases,

and
the resistance
01
the W (wtIite)leg increases.
4.
More current
110ws
in lhe B leg lhan
in
the W leo be-
causa its resislance is less.
5. The mag-Jetic field around coil
<V
is strengthened;
thaI arOl lrd coil
CD
is weakened,
6.
The balancIng relay pivols toward coil
<V,
causing
the movable conlact to move to the left, completing the cir-
cuillhrough
Ihe
Mopen~
molar
winding diraclly.
1.
The
motorbeginstodriveqJen,

and as
ildoes
SO, the
teecback potenliometer wiper also moves, varying the
size
of
resistances A3 and
R4.
8.
The
motor
continues
10
run until
R3
equals A2. and
R4
equals
Rl.ln
olherwords.
the motor runs
unlillhe
IOlal
resistance
in
lhe W leg is equal to the resistance
in
the 8
leg, i.a


the legs are balanced.
Fig.
32
shows just (he controller
ard
reecback poten-
domelers. They are all thai is necessary
10
explain the
0p-
eration
01
a series 90 conlrol circuiL
The
series 90
molar
can
be
driven fulty open or fulty
closed when r9QJired, sil'llJty
by
ShOrting the molar lermi·
nals (Fig. 33). Shorting A
10
8 will drive
the
molar
fulty
317
UR,n


L_-'-'o.:::.::c
__
J
""'TOR
FIG.
31-
SERIES 90
CONTROL
CIRCUIT WITH
THE
lEGS
UNBALANCED.
CONTROLLER
POTENTIOMETER
rY1H1
H1
ft1
000
000
®®0
000
FEEDBACK
POTENTIOMETER
mmmliJ
lUlU
AJIU
II1R4
IU""
1l1'RJ~R2+""

Al'IIJ>IU'1U
Rl'1I3-R2.1U
Al.A3<R2·.
1I0l011
SlOI'P'ED
1I0TOII
AUIIS
MOTOII
SlOI'l'lD
1I0ro"
AU'll
FIG.
32-
POTENTIOMETER
WIPER
POSITlONS
FOR
BALANCED
AND
UNBALANCED
CONDITIONS.
open-remember:
RED
TO BLUE FOR BTU. Shorting A
to W will drive
lhe
motor fUlly closed.
If a controller Is connected
10
lhe

motor, Ihe R terminal
lead must
be
disconnected.
If
II
is not disconnected, lhe
motor will drive to a position delermined
by
the atr'OJI'll of
resistance remaining
in
the nonshorted molor-con!roUElf
leg.
11·91558-1
r-;:::;V;;W:;'SIR'UtoO
CONTROLLER
FIG.
33-SHORTING
THE MOTOR
TERMINALS.
SERIES
90
CIRCUIT
ANALYSIS
USING THE
"T"
Series 90 controllers
and
molors have 135

ohm
JXllenti·
omelers, but for corrpUlalioo purposes, both controller
and
feechack potentiometers are considered \0
be
140
ohms. The simplified diagram used for analysis (Fig.
34)
shows
onlV the controller and the
faedlack
polentiama-
lers, since other resislances are constanl.
tOIllTROllElll'On'HlOMUU
(w)
~
(.
. I

.AN\,
fEEOBAtK
PDTUITIOIlIETER
1411
OHMS
FIG.
34-SIMPlIFIED
DIAGRAM
FOR
ANALYSIS.

With the
molor
and controller balanced, there will be
140 ohms in the W leg, and 140 ohms
in
the B leg. If the
conlrollersenses a change in
(he
controlled variable (pres-
sure
or
temperature),
il
moves lhe wiper over the controller
p:ltentiometer, changing the balance in the resistances
of
the 2 system legs
and
causing the motor to run. The ques-
tion is, which way will the
molor
run, and how far will il run?
Series 90 circuits can
be
analyzed by using a simple
-To arrangement
10
cQl'TC)Ute
the effect
of

changes In
re-
sistance in a circuit. For example, for Fig. 35 (which shows
only the controller and motor feecback p:ltenliometers,
theSE!
being the only variable resislances) the
"r
would
'OM
~~
•
_LoG
HIG
""
,
•,
,.
w
•
!>
~

C,ts,

lOOT""

~V
Bl
OIllvUl
'U""

V OPEN OR
ClQ5EDBV!"ORTING
TNf
"orOA
HA"'N"'l'~
A_I
'010
O'IN
A_II
'00
CLona
•
,
•
look like Fig. 35 when
tN
cootrolled variable Is at the set
p:lint and both wipers are centered.
C/lOfTAOlLOA
FIG.
35-
"r
FOR PRESSURE
OR
TEMPERATURE
AT
THE SET POINT.
The balancing relay coil winding which causes the mo-
lor to drive
qJen

is in the blue leg (Fig. 32); that which
calJSElS
the motor to drive closed is in the while leg. An in-
crease in resistance
in
the while leg will result in more cur-
ren! in the
blue
leg.
and
the motor will drive qJen.
Likewise. an increase in resistance in the blue leg will re-
sull in more currenl in the white leg, and the motor will
drive Closed. We can
ack:l
this information
10
the
"r
as
shOwn in
Fi\;j.
35.
The •
T"
indicates the tact that ack:ling resistance to the
W leg causes the motor
10
open, and ack:ling resistance to
the B leg causes

it
to close.
Assume that a
1all
in the controlled variable causes the
conlroller wiper to
move toward
B,
increasiJ1Q
the R to W
resistance to 100
ohms
and decreasing R to B resistance
to
40
ohms. Remember:
REO
TO BLUE FOR BTU. The T
now
looks like Fig.
36.
We can see that the motor is going to drive open be-
cause the W ieg resistance
is
higher.
How
far will
it
run?
The rule that applies

is-the
motor will continue to run until
the feecback p:llentiometer wiper has
moved over a resis-
tance equal to 1/2 the total difference between
Ihe
R·W
and
R-B legs.
In Ihis case, there is 60
ohms
difference
(170
minus
110); the molor will run
tar
enough
qJen
10
move the feed-
back p:ltenliometer wiper across 30 ohms. This will
rebalance the
"r
(Fig. 37).
Circuit analysis using the T methlXl becomes
espe-
cially useful as additional controls are added to the series
90 circuit.
SERIES
90

OPERATION
WITH
EXTERNAL
LIMITS
There are 2 types
01
exlemallimits
-
(I)
mlXlulaling lim·
its, with a p:ltenljomeler,
and
(2)
Iwo-posilion limits, with
an
spdt switch. A mlXlulaling limit adjusts the molor just
enough to correcl the condition, while a two-position limit
318