FLAME SAFEGUARn CONTRULS phần 9 pdf

We cannOI reOOce lhe Firing Rate Control pressure drop pasr our minimum estimated fi\}Jre of 30 percent of the mani­ 11·97558·1... It we haY'6 5 Regulator Outlet Pressure - Piping Pressu

c It point X 1a/(s only a very short disTance to the right

of the diaoonal line, increasing the pressure drop

might allow use of the next smaller valve size

mated lotal pressure drop over bolh SSOVs

5% of 12.0 = O.S in we

To determine lhe extra pressure drop, move upward

to the Pressure Drop Scale fo find the pressure drop

needed for a 2 inch valve In this case, the actual pressure

293

6.4 - 5.4 = 1.0 in we

Using a 2 inch varve may still be p::>ssitJle The actual

wc The diHerence between the eslimatad and actual

manifold to keep the required burner inlet pressure We cannOI reOOce lhe Firing Rate Control pressure drop pasr our minimum estimated fi\}Jre of 30 percent of the mani­

11·97558·1

FIG 8- PRESSURE DROP VS CAPACI'N FOR A 'NPICAl BUlTERFlY 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

pressure regulator SSOVs and Firing Rate Control, plus

repealing the sizing procedure

SIZING CHART FOR FIRING RATE

CONTROL VALVE

Valves SinCe a Butterfly Valve ctleS no! provide light clo­

l4)slream

In our ellample the eslimaleO pressure drq:J across the

liring rate control is 6.5 inches wC wilh a capaCity of 10,500

cfh at standard conditions

a If SSOV estimaled <md actual pressure drop are lha

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·

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

y,

nearest slanteO line below In lhis case, we have a 2 inch valve with a 40 degree opening

V5055 VALVE SIZING NOMOGRAPH

Non, II ",,",.1 ' "1'0.,10< " " 0."1 ,,~ o J Dr I G) ''0'" ··C~" ~ '0

,k'Q , , _ on• •nd , ' " "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 ,i,,,.

, _ '~"""'''Q_ aI t,"" (!)

·· C",·· ,.t ,'h' t" ,

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

Valve Sizing Char1

2 Valves Piped in Series

295

For this chart, we need to know the inlel and outlet pres­sure for the V5055

1 Determine inlet pressure for V5055 When 2 valves are

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'l­Ie! Find the piping lOSS flQJre tram Fig 3 It we haY'6 5

Regulator Outlet Pressure - Piping Pressure Drcp

pressure equals lhe inlel pressure minus the pressure drcp across the valve

71·97558-1

"

, ,

NOTE: Since we calculated the corrected capacity

lines 1 and 2 In lhe 1,'5055 Valve Sizif'l;l Chart

direcllol"6

inches we by (he conversion 1aclor1rom IheAPPENPIX

10 gel the correct psi unl!

14.6 )( 0.0361 = .527 pst

4 Draw line 4 trom 10,370 cfh on the Burner CFH Gas

3, fa the valve site scale 12 inches)

EXAMPLE 2

Determine the 1,'5055 Valve sizQ from lhis job's

5j:lElciflcat ions:

Inlel Pressure Available at 1,'5055 13 Inches wC

Eslimated Pressure Drop

••

SOLUTION

calculate cfh required

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

units

6 In we )( 0.0361 '" .216 psi

CONVERSION TO STAHDARD CONDITIONS

STANDARD CONDITIONS

-"'061 valve sizing charts provide coordinates under a

corditlons are:

1 Capacity - cubiC; feel per hour lcfh) ConverSion 10r­

CONVERT CAPACITY TO 0.64 SPECIFIC GRAVITY

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 =

Btu/cu

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

To find cFh itt .64 op gr, mwtiply cfh at "x" ,p, qt,

iD find "Fh at "J<" sp qt, divide cFh at 64 "p gr by conversi\ln faclor

CONVERT CAPACITY TO SEA LEVEL AL TITUOE

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

PRESSURE DROP CONVERSION

; 4 in wc 2This conversion IS nol otten needed because rf105t

(Convert

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

'.­

I N T R O D U C T I O N - - - ­

DEFINITIONS

1119 firing Crate is Jhe combustion rate II is the rate at

which air, fuel, or snair-fuel mixture Is supplied loaburner

gas or gallons of oil), weight (tons of coal), or heal units

control (or combustion control) is simply a means of regu­

ply according to load dernard

PURPOSES

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

sure, furnace draft, waler level and steam lemperature It

FACTORS AFFECTING THE FIRING RATE

the primary consideration other faclors also affect the fir­

much of the lotaf heal produced, opening and closing

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

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

turndown ralio Is particularly desirable for batCh-type fur·

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

extinguished

Flashback limils the minimum firing rate A flame

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

draft are forced and indUCed draft

Forced draft is produced by a fan or blower located at

draft is produced by a partial vacuum within the corrous­

cMlTtler

temperature of the atmosphere, height Of the stack, direc· tion and force Oflhe wind, and other environmenlal condi­tioos 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

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

71-97558-1

automatic regulation, an automatic firing rale control sys­

cOl'l'b.Jsl:lon Some of the automatic systems used will be

discussecUn this section

AUTOMATIC FIRING RATE CONTROL

SYSTEMS

vide firing rate control Initially, the syStem is Iriggered by a

disturbanca then causes a sequence of adjl lStJTlentS, In

parallel or in cascade (series), to control the various parts

For exa~le, in a parallel system, a change in steam

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

an adjus1manl of Ihe induced draft, and lhe resulting

ct\aIlgEl in furnace pressure is then corrected by a change

in the forced draft

eral classes-paranat, serieas·fuel, sories-air, or calorime­

classes Usually, one particular syslem (or combination)

a healing furnace) generates an error signal The error Sig­

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

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

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

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

liq,Jid fuels, and even pulverized coal A series sysIem is generally considered to be very effective in controlling the

the flow requirement of the other

Because airflow Is the dependenl variable, air will not

supply at limes When lhere is a fuel shortage, the system

would deCrease the effectlve heat El\l'9n further

However, if the air SlWly fails or airflOW' Is reduced ex­cessively by a fan failure, there is a danger of filling the fur­nace 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

by a predelermined amounl Also, a flame safeguard con­

combus-RATIO REGULATOR

FUEL FLOW

ERROR SIGNAL

_.J_-,

I ALTERNATE I

'LOCATION •

OF RATIO • : REGULATOR

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

IhQ airflow Measuremenl of thQ ail1low then produces a

sig~ that controls the fuel flow Thus if the airf/(lW fails,

readlly measured

CALORIMETER CONTROL SYSTEM (FIG 4)

In lhe calorimeter control system, the error signal CCll'l­

produces a signal thai is used 10 control ail1low, The

amount 01 steam produced is proportional to the firing rale

uring steam flow Because stearn flow is substituting for

fuel flow, the ratio regulator is in the steam flow clrcuil

given fuel that will release a certain amount 01 heal If the

rate of heat release is known, the amount of air required

p::>rtionalto the rate of heal release, so a measurement of

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

the system to correct the steam flow for standard conditions

fails A decrease in airllow will decrease the heat release, which will deCrease lhe steam !low, causing a further re­duction in airflow Meantime, the system is calUng for more

case, steam flow instead of fuel flow is CClI'1l)3.red with airflow

AIR-FUEL RATIO REGULATORS

control, and (3) flow control All 3 actually keep the flow

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

If one valve rolates through a 45 degree angle, the other will also rolate through a45 degree angle: and If this move­ment causes a 25 percent chaf1Q8 in the flow rate of ona fluid it will cause a 25 percent change in the flow rate of

AIJ'lfLOW

ERROR SIGNAL

FUt:L FLOW

RATIO REGULATOR

AIRfLOW

I

RATIO REGULATOR

"

FIG 3-SERIES-AIR CONTROL SYSTEM

71-97558·1

ERROR STEAM

I

RATIO REGULATOR

FIG 5-TYPICAL AIR-FUEL RATIO REGULATOR

~srion Handbook by North Amedcan

MfQ Co., Qeveland, Ohio.)

mixture at others

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

variali~

The resistance to flow downsTream trom the clYltrol

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

(01' air if the regulalor Is In Ihe air nne) until the pressures are the same

$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

used for counlerba.lancing the weights of lhe shaft, plug

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 pres­sure proportional to Ihe pressure elrertecl on the tc:p side of

on the air diaphragn, lending 10 move the valvs shaft as­

up on the oil diapnragn, tending 10 raise the valve shaft

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

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

striction measures the flow thtough that line Both pres'

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

upstream and downstream Il'Jl=Iulses from an orifice in the

larly', impulseS from the air line act on the air diaphragm so

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

that equal pressure drops correspond to the correct ratio

01 flow rates The ratio regulator also has a manual adjust·

,

FIG 7-iYPICAL AIR-OIL RATIO REGULATOR

USING PRESSURE CONTROL (From

Combustion Handbook by North American

Co., GJevs(and, Ohio.)

FIG a-TYPICAL AIR·GAS RATIO REGULATOR USING FLOW CONTROL (From Combustion

Handbook try North Amen'can Mfg Co., Oeveland, Ohio.)

FIRING RATE

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

guard pr~ammlng conlrol programmer)

er"lCJl 91 heat This is the most efficient method because

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

tained by simultaneously PJs!tioning lhe dampers 10 aO'nil more combustion air and the fuel valve to admit more fuel

more fuel.l High·low firing is used on large, commerCial

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

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

marlCt The burner lights off at low tire 1l1en a controller

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

PREPURGE CONFIGURATIONS

oorner Iighl-otl, to remove any fuel or fuel vapors that may

methOOS at tiring The ~high fire" Is really a l!!i~().I!I.!§Ir

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!

period when the burner Is firing

heat, the prepurge period aclually COOls the system OOwn

flrinQ are summarized in Table I Insurance comp9.r'1ies in­

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

low fire p.:lSihon before ignition trials, and drives il back

open 10 high fire for the run period

LOW FIRE PREPURGE

used anymore in flame safeguard awlicalions Firing rate

er motor at ils low fire position until after i'7lillOn trials,

control of a series 90 pressure or temperature conlroller

TABLE I-PAEPURGE CONFIGURAnONS

1-wireb

UL Modulating

(2-stage firing)

R4181A1042,-A1059

<&"-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

d Low fire switch stops sequence before ignition trials until low fire position is proven

I Switching returns firing rale motor to its low tire position when the run period is OVer

LOW-HIGH-LOW PREPURGE

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

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

PROVED LOW-FIRE-START INTERLOCK

which is outdated and seldom used anymore) This inl9f­

maximum) betote the burner can be iglited This is usually

SWitCh) mounted on the drive Shaft or the firing rale motor The auxiliary switCh is wired inlo the safety conlrol (pro­grammer) 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

!hrOU<tl the combustion charrber The hit;1'l tire swllch Is usually also an auxll1ary switch on the firing ratelOOlOf'

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 For a complete description ollhe 0p­

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

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

position

"flow is e!tab\ished, Ihe airtlow switch close's, er'oergili~

switch, jurrper, and M108) TIle actuator drives the darrq>­

er open ~o high lire ~ition)

s:ops the timer until the low fire swilCh closes, proving thai the daf1lJ9r is in ils low fire position before ignition trials

closed during most of this period Near lhe end of ignition trials, al ti9.5 seconds, M108 closes The damp€lf actuator

& ~T""To AM , ,~ 5"' v ""''' lOON IUAC S.CC"""

& , -A , T ,.UA"lICI.""ffN U 'NAU" .O

A IN CA""~ ACTUATM ,S"IlC,

11A'·I'O:I'''''''._'''~·.I'''''N AUU.HOII " D rocoorr"OL tNE

FIG '0- TYPICAL TIMER SEQUENCE CHART

FOR '-WIRE (OPEN DAMPER) FIRING RATE SWITCHING

and I'" damper stays open during the run period

closed

3-WIRE FIRING RATE SWITCHING

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

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

-FIG, 11- TYPICAL 3-WIRE FIRING RATE

SWITCHING

FIRING RATE SWITCHING,

FIG 12-TYPICAl TIMER SEQUENCE CHART

FOR 3-WIRE FIRING RATE SWITCHING

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

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·

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

connecting the A terminals of the molar ar.d controller

The firing rate motor is released to mcx:::Iulate under conlrol

period

the timer slarts Al 118 seconds, M9A opens, cpening the

drives the molar and damper closed

4-WIRE FIRING RATE SWITCHING

a firing rate molar .ith a spring-return or spring-biasecl

balanCing relay Therefore newer A4150G ard Lmcdels,

FiQS 13, 14, and 15 show the firing rale switching 01 a

I'T'ICX1els have provisions only for the low 11re switch

motDl" (Fig 14) Is energiZed IhroU(1l MJA Al 3 seconds,

minals Rand B on lhe 1iring rate motor The motor drives

provide maximum airtlow during prepurge, the timer motor

prspurga continues

At 20 secondS, M3B closes (Fig 14), bypassing the high fire switch At 26 seconds, M10A opens (Fig 13)

FIG 14- T'(PICAL OPERATION OF HIGH FIRE

AND LOW FIRE PROVING CiRCUITS