flame safeguard control phần 7 pps

Honeywell pressure controllers available or bellows responds 10 pressure changes and, throu;j1 IS for use In these systems wltJ be described In he following mechanical linkage, acluates

W arcI make R to B when the conlrollEld variable falls 10 the

sat point minus the differential

A controller w!lh an additive differentIal operates simi­

larty e.~CBpt that the set point is al the/ow end of the differ­

enliallnslBad at at the hiQh erd

A controller with manual reset (also callEld lockout) can

beUMd as a limltta (1) shut down the System it it braaks a

Circuit or (2) ~rate an atarm It makes a circuit On most

CCJ1lrol1e~ wilh manual reset, lockout occurs at the sat

point, but on a few rT'l(XjeIS it occurs at the sel point plusor

minus-the differenlia.!' The circuli will stay lockEld out until

the ternperaturereturns 10 normal (lockout point plus or

minus the diNerenllaQ and the ~rator depresses a man­

ual rese! rever or button (Fig 2 or 48) It the lever or bullon

has a trip-free feature, operation will not be returned 10

in by tape, wire, or some other device Manual reset makes sure someone is going to notice 6Ol1l8thing is wrong A good servica lechnician will correcllhe prOOIAf11 before reselling the switch

PROPORTIONING RANGE Tha proportiOning range (also caliEld Ihrottling range usually edends above the set poim (Fig 9) alihOugh Qrl some controllers it extends on lxlth sides 01 the set point Pressure or temperature variations cause the bellows or diaphragm to move, caUSing the potentiometer Wiper (R lerminall to move across its windings This varies lhe re­sistanCe between R and B, and Rand W The resu1ting cir­cuit urtJalance drives a modulating motor or mod:.JlalinQ valve aCtuator and regulates the firing rale (For a detailed explanation of this operation, refer to the Flame Safeguard Reference on Firing Rale Controls, 10rm 70-8117.) As the controliEld variable rises, the Wiper will move toward the W end of lhe potentiometer, driving the motor or actuator to­ward its Closed position ard decraasing the firing rate As lhe controliEld variable talis, lhe wiper will move 'award the

B end, driving the motor or actuator toward its open posi­tion and increasing the firing rate Thus, a CharlQ8 in the controllEld variable wilt cause modulation of the firing rate

10 compensate for fhe Change and keep the pressure or terrperalure nearly CQrlstanl

- c o ,,,

I I

T T'ON'NG~"'OPOR­ I ( POTENT'O"UER

Ii::,

"''''lOG' (",~~;j]

-NIGNFlIlE 10'ENI

On some controllers the proportioning range is 1ixed,

while on others it is adjustable On adjustable models, the

proportioning range scale is usually graduated tram A to F

.'!yith a MIN (minimum) value below A The value of each

division depends on the cperaling raf1Q8 and set J,)Oint at

the controller Proportionlng range charts like the one

shown in Fig 10) are available for different cperaling

ranges to determine the pr~ seuing (The propor·

tioningrange scales of some t~ralure controllers, like

the T991A ~d B, are marked directly in degrees For q

FIG 10- TYPICAL PROPORTIONING RANGE

CHART FOR A CONTROLLER'WITH AN AOJUSTABLE PROPORTIONING RANGE

CHECKOUT AND MAINTENANCE - - - ­

CHECKOUT

After the controller has been installed, wired, and set, it

should be tested with the system in operation First allow

the system to stabilize Then observe the operation of the

controller while raising and lowering its set point Pressure

or temperature should increase when the set point is

raised and decrease when the SElt point is lowered Use

accurate pressure Of tef'11)erature testing equipment

when checking out the controller Do nOI rely on inexpen·

sive gauges

For an on·off controller make sure the swilch makes

and breaks at the proper points Be sure to consider the

differential If the controller is ~£1ad ol operatinglffi­

properly, it may be further checked as lollows:

, Disconrlect the wires from the controller

2 Connect an ohmmeter between the switch terminals

3 Raise the set J,)Oint of the controller more than the dif­

ferential, The switch should either make or break, depenc:J

ing on the model of the controller (11 it makes, the

If a proportioning controller is suspected of operating

ohmmeler will read zero; if it breaks,

imprope~ly,

read infinity.)

1 Disconnectlhe wires trom the cOf1troller

4 Lower the set point of the controller more than the dif­

2 Connect an Ohmmelel between cOf1trolier terminals ferential The switch shoold break or make, depending on

8 and W to measure the resistance at the potentiometer inits action in step 3

the controller The Ohmmeter should read about 135 Ohms

5 An approximalion of the differential can be made by

or 270 ohms, depending on the model 01 the controller observing the change in set point r9QJired 10r a resistance

3 Conneclthe ohmmeter between cQnlroUer terminals change from zero to infinity

Wand R and raise the set point of the cOf1trolier above fhe For a proportioning con/roller make sure the modulat­ actual pressure Of' temperature being measured The

ing motor or modulating valve acluator reaches the low ohmmeter should read the full value of the J,)Otantiomeler and hiQh fire J,)Osilions at the proper points If the motor or measured in step 2 (135 or 270 ohms)

actuator runs in the proper direction when (he set point is 4 Slowly lower the set J,)Oint of the controller while 00­adjusted, il can be assumed that the controller is operating serving the ohmmeter reading The resistance should properly It it runs in the wrong direction, reverse the 8 a.nd drq) to zero at some sel point below the actual pressure or

W wires Observe the action of the motor or aCluator tosee temperature

if it stabilizes If the motor or valve is moving cOf1stantly 5 An approximation at the proportioning raf1lijJEl can bEl widen the proportioning raf1Q8 (if it is adjustable) a lillie at made by observing Ihe chaf1Q8 In set J,)Oint rElQUired tor a

a time, unlil the system is stable resistance change from zero to full value

CALIBRATION

AU controllers are carefully tested and calibl"aled at the factory under controlled conditions If the actual ~rating preslil,lr.es_ or terrperatures 00 not malch the set points, most controllers can be recallbrated in the field FirSI

slsl of occasional inspection and blowing or brushing away any accumulaled dirt and dust To ensure prq:er functioning of lhe controller at all times, an ~raUona!

check of the Mtire system Should be performecl wring routine maintenance checks

check lhat the controller is level (i1 it hasa mercuryswilCh)

Ralevel il if necessary, and recheck the ~raling points It there is still a discrepancy:

1 On 6Om8 controllers, the scaleplate can be moved slightly L;lP oroowQ u(\111 the sat point agrees with lhe actual pressUre 0( tef'rl)erature

2 On other controllers, the set point Indicating dial can

be turnecl with a special calibration wrench until it agrees wilh the actual pressure or terrperature

MAI~TENANCE

The ,cover of the controller should be in place al all times to protect the internal components tram din, dust, and ~ysical damage ROUline maint9l'lBnce should con­

-,'

Occasionally, mishandling of the controller may cause

a malfunction A gradual change Of control point may oc­cur because of a very small leak In the lhermal system On temperalure controllers, this Is mosllikely to be causadby bending the capillary tubing too sharply, or too close to a joint Aging althe factory would have revealed the leak if it had been presen1 at the lime of assembly If/he tLbing is squeezed so hard or bent so Sharply that ils bore is com· pletely closed l,4), the controller will, of course, be ren­dered entirely in~ralive Deforming the bulb (or Olher sensing element) will change the VOlume, resulting in a Shift in calibration Tnese ~ of malfunctions should be lool<ed for ciJring maintenance Controllers should be han­dlecl carefully althe time of installation, et.Jring actual use,

and during mainlenance

222

, .~

A pressure controller is a device thai monitors the pres­ waler heating systems, In gas burner systems, and in oil

sure of sleam, air, gases or /iQ.lids AA internal diaphragm burner systems Honeywell pressure controllers available

or bellows responds 10 pressure changes and, throu;j1 IS for use In these systems wltJ be described In (he following mechanical linkage, acluates a switch or polenllomeler to sections Installation procedures peculiar to each system keep the pressure within predetermined limits Pressure will also be diSCUSSed

controllers afe com~nly usaa' on steam boilers and hoi

PflESSUFi"E CONTROLLERS USED ON STEAM BOILERS AND HOT WATER HEATING S Y S T E M S - - - ­

The pressure controllers discussed in this section can

be used with steam, air, noncombtJslib!e gases, or fluid

noncorrosive 10 the pressure sensing element They pro­

vi~ operating control or limll protection, depending on the controller model al"d wiring hookup (Figs 3-7/

LOCATION AND MOUNTING When used with sleam boilers, always mount the con­

troller above the water fine in the boilEir A steam trap must

always be connected between the controller and the boiler

(Fig 11) to prevent boiler scale and corrosive vapors from atlacking the diaphragm or bellows The 1<::q:1 on the steam trap must always be perpendicular to the face of the con­

troller 11lhe f<::q:l is parallel to the contrOller, expansion or contraclion 01 the 1<::q:I will tip the controlier and cause the switch to operate inaccurately

The controlier can be mounted (1) alongside the pres­

sure gauge, (2) in a filling on tile boiter provided by the manufacturer, or (3) at a remote location in case of exces·

sive vibration When making pipe conn&ctions, use pipe compound sparingly to seal tile joinlS Excess pipe c0m­

pound may clOQ Ille small hole in tile fitting al"d prevent the controller 1rom operating properly

.& l/O-'''C," BLACK 'RO" ~'~E WI'," ,/ ,a NPT [XTER l

T f OS Oil BOTH ENO~ , ,e

BOILER

FIG 11- RIGHT AND WRONG MOUNTING OF A

STEAM TRAP, WITH APPROXIMATE DIMENSIONS IN INCHES

[MILLIMETRES IN BRACKETS]

NOTE: If using tile controller with a CO!T'Pressor, install a dampening device (wch as a needle valve header, or surge lank) to dampen pulsations which can damage the controller or reduce its life

To mounllhe conlroller alongside the pressure gauge

(Fig 11), remove the gauge In its place install a steam trap with a lee on tap Using elbows and pipe nipples, mount the controller and pressure gauge on the ends of Ihe tee

If it is not convenient to mount lhe controlier alongside the pressure gauge, install a steam trap in the fitting pro­

vided by the boiler manufacturer If there is no 1ilting mount the steam trap al a location recommended by the boiler manufacturer Screw Ihe controller directly to Ine steam trap

If there is ex.cessive Vibration at the boiler that mayad­

versely affact the operation of the controller, the controller

should be mounted' at a remote location All piping from

the boiler must 'os suitable and solidly mounted The pip­ing must be properlV pitChed to drain all cOndensation back to the boiler A steam trap must be mountEKl between the remote piping and the controller

HONEYWELL PRESSURE CONTROLLERS AVAILABLE FOR USE ON STEAM BOILERS AND HOT WATER HEA,TING SYSTEMS Honeywell pressU/8 controllers are fistEKl in Table II al the el"d 01 this section along with their applications, switch types, al"d operating pressure ranges

Fig 12 shows the mcx:lels IiSIEKl AlIl'T'\Ode1s operate as

desCribed in Basic Principles ot Controllers except the

P455 which is a corrtJination prq:;ortioning al"d on-otf controller lis operation is descri'osd next For furttel infor­mation, refer to the instruction sheers tor the controllers OPERATION OF THE P455 COMBINATION CONTROLLER

The P455 is a combination prq:;ortioning al"d cn-otf

pressure controller [n addition to a prorortioning potenti­ometer, it has an spst swilCh with a subHacUve ditferenlial

that breaks on pressure rise Tha main scale is set at the

manmum pressure desirEKl The differential is adjustEKl in­

stead of the prcportioning range Tl"le proportioning tange will automatically be sat 10 approximately 85Percent of the

differenlial (The differential sca[ap1ale is graduated from

A to F with a MIN value below A Refer to the P455 instruc­tion sheet for values 01 the differential and proportioning range.)

FIG 12- HONEYWEll PRESSURE CONTROLLERS AVAILABLE FOR USE ON STEAM BOILERS MID HOT

WATER HEATING SYSTEMS

'.'

The P455 also has a UNISON/SEQUENCE adjust­

ment, which provides a choice 01 firing rale at burner startl.P The odjusling dial is located just below the wiper armof the potentiometer (Fig 2?) The dial is turned so Ihe arrow is at Uforunison q:)(lralibn, at S for sequence cpera·

lion, or at one of 3 inlermediale positions, Fig 13 sh(w,rs the operation at Ihe P455 for each of these p::lSitions

In (he UNISON position, Ihe prcportioning range is: en­

tirely within Ihe differential range, so the on-ott swi'ch and the prClJX)rtloning potentiometer are functioning at the

same Ifme When Ihe pressure falls to the sel point minus the differential, Ihe on-oN switch makes and the burner Is lumacl on The potentiometer wiper is aU the way over to the Bend, lhe firing rate Controls are a! the high fire jXlSi­

tion and the bUrner starts al high fire, As the burner heats l4=l and the pressure increases, the wiper moves toward the W end of the potentiometer It the pressure contlnues

10 Increase, the Wiper moves all the way to the Wend and

!he firing rate conlrols are at the low tire ~ilion Ordinar­

Ily, modulallon keeps the pressure belW9Eln thess posi­

lions within lhe proportioning range If It prOblem devek:ps

or the Iced drops suddenly, and the pressure continues 10 rise, the on~f'I' switch breaks and shuts down lhe bUrner when the pressure reaches lhe main scale sel point

In the SEQUENCE posilion, Ihe prqx>rtionlng range is

entirely below Ihe differenlial range, so the on~ff switch and the proportioning potentiomeler are not funclioning al

224

the same time As in the UNISON position, when the pres­sure falls 10 lhe sel point minus Ihe differential, Ihe on-off switch makes and the burner is turned on However, the potentiometer wiper is all the way over to the Wend, the 1iring rale controls are al the low tire position, and the burner starts at low fire, It the pressure continues to fall be­10re the burner can heat up, the Wiper moves toward the B end at the poten/iometer If the pressure 1alls far enough, Ihe wiper moves all the way 10 the B end and the firing rate controls at the l1igh fire posilion As the burner heats l.4)

and the pressure increases, the Wiper moves toward the Wend at the potentiomete( Again, the pressure is ordinar­ily kept within the proportioning range t1the pressure con­linues to rise, the wiper moves all the way 10 theW end and lhe 1iring rale contrOlS are at the low tire jXlSilian The burner slays at low 1ire as the pressure increases through the differential range, and is Shut do ·:n when Ihe pressure react'19S the main scale sel point

In an intermecliale jXlSition, the proportioning potenti­ometer is functioning partly wllhin the differential range of the an~N switch-the amount varies with the ~ilion This provides a ChOice of lhe firing rale-somewhere be­tween low 1ire and high fire-al burner startl4=l when the

on~ff switch makes As shown In Fig 13, the pressure range over which the burner will operate at low fjre also varies with the position 011he UNISON/SEQUENCE dial

PRESSURE CONTROLLERS (PRESSURE SWITCHES) USED

IN GAS BURNER SYSTEMS

The pressure controllers used in gas burner systems are commonly called gas pressure swilchas_ They may be

used with natural gas, LP gas, or air (The C64sC and D models can be used only with air.} They provide safety shutoff or diflerential-pressure control, depending on the controllsr model and wiring hookup (Figs 3-5) No propor­

tioning controllers are available tor use in gas burner systems

LOCATION AND MOUNTING

Gas pressure switches in the main burner line should

be located downstream from the PRII (pressure rBgJlaling valve) The low gas pressure switch should be localed u(r

stream from the safety shutoff valve(s) In a downstream location, there would be zero preSsure when lhe burner Isn'( running and the safely shutoff valve(s) is closed This could prevent startup or reqUire manual reset every time the burner is started The high gas pressure switch should

Screw the main pressure connection ot Ihe pressure switch to the pipe nil=flle The main connection is a heJt­

agonallilling with 1/4 or 1/2 inch NPT Internal threadS To avoid leaks and damage to the case use a parallel jaw wrench on the hexag::mal fitling close 10 lhe pipe ni~le Make all connections carefully and lest lor leakage Do not

tighten rhe pressure swifch by hand by holding the case

In some cases, it may be more convenient (0 mountlha pressure switch on a nearby wall using the optia'lal mounting bracket The braCket should be Installed before connecting the piping from the main line

ContrOllers with mercury swilches (C437 C447, C637,

(;647) must be carefully leveled as described In Basic Pri"

71-97558-1

RATE

SSOV CONTROL

o MSOV MAIPIl

VENT 'RV

o may be mounted in any position, but they are slighlly vented into the combustion Chamber or to another more accurale when mounled with the diaphragm hOri· safe place in case the diaphragm in the pressure zontal The C645C (low operating pressure range) must switch fails,

be mounted with the diaphragm vertical and (he vent con­ b DifferentjaJ pressure-Connect the high pressure nection (bleed fitllngl at the I:ollom side at the system to the main pressure connection,

is provided on all pressure switches This connection must Cation cannot be used with hazaroous gases as no

c Negative prflSSUre - Connect the low pressure side

~AS ~~tsSV~E: SWITCH

- - IAT RIGHT ~GLE:S TO

THE: M.'~ ~I'E: L'~E)

FIG 15- MOUNTING A GAS PRESSURE

SWITCH DIRECTLY ON THE MAIN

PIPE

to the vent connection This awlication also cannot

be used with hazarcbus gases, When using a pressure switch with a low pressure range, momentary pressure surges or &bumps" can cause the switch to break Orifices are available for C437 and C637 Pressure Switches to eliminate or reduce chal· lering or nuisance lockouts caused by Ihese -bumps.· An

orifice is inserted in the main pressure connection (Fig 16) [0 reduce the effect at pressure surges The bushing and

ORI FICE TOOl.­

AG 16-INSTALLING AN ORIFICE IN A C437

OR C637

226

onfice 1001 shown are used only for installation at the ori­

tice, and are removed afterward

PRESSURE SWITCH SETIING

Industrial Risk Insurers (formerly F.LA.) recommenc1s

that gas pressure switches on the manifold be seln accor­

dance with the turncklwn range of Ihe installation They

recommend thatlhe high gas pressure switch be sal 20

per,cent above Ihe maXimum firino rate pressure, and the

low gas pressure switch be set 20 10 50 percent below the

minimum firing' rate pressure, wilh the preference being

HoneyweJl pressure conlrollers evailable are listed ;n Table II al the end of Ihis section, along with their awlica­tions, switch types, and operating pressure ranges Fig

17 shows the models listed, All models operale as d&­scribed in Basic Principles 01 Controllers For runher infor­mation, reler to the instruction sheats for the controllers

SySTEMS

Prassure controllers are used in oil burner systems to

supervise oil pressure and to supervise the pressure 01 the

atomizing medium (if used)

OIL PRESSURE SUPERVISION

The Oil pressure controllers (also called oil pressure

SWitches) discussed in this section can be used with any

type of fuel oil, inclUding heavy preheated oils They have

a stainless steel diaphragm to resisl corrosion The dia·

phragm transmits changes in oil pressure to an spst mer­

cury switch Ihrough a mechanical linkage

The L404T and Ware high pressure limits; they break a

circuit and st'1ut down the system if the oil pressure gets

too high The L404V and Yare operating controllers and

low pressure limits: they preventlhe system from staning

untillhe oil pressure is high enough, and they Shut down

Ihe system ir lhe oil pressure falls too low TIle L404T and

V have adjustable subtractive differenhals: the L404W

and Yare manual reset models

hiGh oil pressure switCh should be located as near the burner as possible

An oil pressure controller is mounted directly on the main pipe by inserting a tee in tha pipe line and cOnnect­ing a pipe ,iJ:Ple of appropriate size to lhe tea (FiQ 19) Screw Ihe he:tagonal fitting (1/4 inch NPT with internal

threads) at the pressure controller to lhe pipe niJ:Ple To

avoid leaks and damage to Ihe case, use a paralle! jaw wrench on the hexagonal filling close to the pipe niJ:Ple

Do not tighten rhe pressure contro/ler by hand by holding the caSe

FIG 17-HONEYWEU PRESSURE SWITCHES AVAILABLE FOR USE IN GAS BURNER SYSTEMS

RECIRCULATING CONTROL

proved 5tandardi Use only a small amount of pipe com­

pourd 10 seal the connection joints Excess pipe

Corrp:lUnd may Clog Ihe small hole in the filling and pre­

vent the controller from operating prcperly

When used with preheated oil, a siphon 10ClP must al­

ways be connecteCl between the controller and the main

pipe {Fig 20) to provide thermal buffering The 10ClP must

always be perpendicular to the face of the controller If the

10ClP is parallel 10 the controller, expansion or contraction

of the 10ClP will tip the controller and cause the switch to

cperate lnaceuralely

Oil pressure controllers have· mercury switches, so

they must be leveled for proper operation If mounting di­

rectly on the main pipe (Fig 19), install the controller at

rIght angles to the pipe; leveling can then be accom­

plished by turning the pipe 100 If using a siphon 10ClP with

prehealed oil (Ag 20), leveling can be accorTfJIlshed b)I

carefully bending the siphon 10ClP The controller is level

when the leveling indicator hangs freely with lis pointer di­

rectly over the Index mark on the back of the case (see

Rg.2)

WIRING HOOKUPS

If the oil burner system is a single burner system with an

integral oil pump, connectlhe oil pressure controller In se­

ries between the flame safeguard control and the main oil

valve solenoid (Fig 21) If it is a single burner or a multibur­

ner system with an external oil pump, connect the oil pres­

The L404B Pressure Controller, designed tor use on

steam boilers and hot water healing systems, is recom­mended tor (his appllcallt:rl It has an spst mercury switch wilh an adjuslable Slblraclive diMerenlial The switch makes a circuit when the pressure rises to the set jX)int, and breaks when the pressore fcllls to the set point minus the differential (see Fig 8) The L404B is available in 4 0p­

erating pressure ranges, from 2 to 300 psi

LOCATION AND MOUNTING The L404B is mounled in Ihe supply line for the atomiz­ing medium (Fig 18) Follow the same mounting instruc­lions as for the ofl pressure c?1trollers

WIRING HOOKUPS The cperation of the L404B Is the same as for the L4D4V,Y (makeS on pressure rise to setjX)int) II should be connected In series with lhe oil pressure controller (Fig 21

or 22)

, /Oll PJtU,5UR£ ~ONTFlQLlE~

., (Ar "'G"r ANGLES TO THE "' ".E UNE)

.'.fTEE (lU"" TO U\I[L

LOOP

•

Oil PIlUSWI[ CONHIOllER

•

PflEI'iE",Tl:O OIL PREl'itATED O'L

SUP'PLV LINt SU","L.II 1,.10'[

& (, eli eLACI( IRON "P[ WITH 1/""'"PT [)(TEIlN 1

THREAOS Oil BOTH ENDS 8tHD TIiE SIPHON LOOP TO

LEVEL THECONTIIOLL.ER

I

"F'"GC".-=2-=O-_-CR "'-=GC"H::T"AH :cC"O:cC"WC"R"O"NC"G= =M"O"U-N='::N"G-O"F"A" ­ -CT

SIPHON LOOP, WITH APPROXIMATE

DIMENSIONS IN INCHES

[MILLIMETRES IN BRACKETS)

HONEYWELL PRESSURE CONTROLLERS

AVAILABLE FOR USE IN Oil BURNER

SYSTEMS Honeywell pressure controllers allailable are lislad In Tabla II al (he end or this section, along with their awica·

!.ions, switch types, and operating pressure ranges Fig

23 shows the models listed For further infonna(ion, refer

to the instruction sheets lor lhe con/rollers

AN INTEGRAL OIL PUMP

FIG 22- HOOKUP OF AN Oil PRESSURE

CONTROLLER USED ON A SINGLE BURNER OR MULTIBURNER SYSTEM WITH AN EXTERNAL OIL PUMP

L.O&Oo&T,V,W,Y

FIG 23- HONEYWELL PRESSURE CONTROLLERS

AVAILABLE FOR USE IN OIL BURNER SYSTEMS

(pounds per SQJareinch), or In oz./in (ClUl'lCeS per S(JJare

inch; 1 oz./ln.' = 0.0625 ps~ Those which extend into a

vacuum range (prescurK below atmospheric pressure

Which 15-0 pslg or ~rQ){imalely 14.7 psial are mar1<:ed in

In Hg (inches of mercury; , In Hg "" 0.4912 psi) Many

scaleplales are also marked in metric equivalents, such as

mm ,we (milllmelres of water column), mbar (millibars), kll1

cmr (kilograms per squate centimetre) or kPa (kilopas­

caIS) SOme international models are marked in kll1CfT11

and kpa Table I lists conversions befween II18se units

SETIING ON-OFF PRESSURE CONTROLLERS

The main scale is SEll at the desired ~ralingpressure

by turning the main SCale adjus\irQ screw (Fig 24) or Inter·

081 dial (0447, C647J unlJl the main scale selling indicator

is al thedBslred value On some models, the differential is

fiXed; bJt on ITOSt I'TlOd9ls it is adjustable by turning lhe

differential adjusting screw (Fig 24) or internal dial

(PA4Q4) until the differential tatting indicator Is at the de

sired ~akJe Manual reset models are reset by pushing in

and releasing 1he manual reset lever (Fig 24)

SETIING PROPORTIONING PRESSURE

CONTROLLERS

The main scale Is set allhe desired q?eraling pressure

by luming the main scale adjusting sere (Fig 25) unlillhe

main scale se1ting indicator is at the minimum pressure

desired (excepl the P455, which 'was d8scribed ~revi

ouslyl TIle oroportioning ranoe (also called throWing

range) e.:tends above this value, as shown in Fig 9

The proportioning range may be fixed or adjustable,

depending on :he controller model An adjustable model is

sel OJ turning the proportioning range adjusling screw

(Fig 25) untillheproponioning rangesel!ingindicalor is af

the dasired val~ "Fha prop::>r1iQlling range scale is

gradu-TABLE J-PRESSURE CONVERSION gradu-TABLE

ated from A to F with a MIN (minimum) velue below A TIle

value at each division depends on lhe pressure range of the controller (Refer to the instruction sheet for the con­troller 10 deleJ:nine the value.)

WIPER AR"'ISI

FROPORT'ONIN(; RANGE

TABLE II-SUMMARY OF HONEYWELL PRESSURE CONTROLLERS

PRESSURE RANGES AVAILABLE

NO LOWEST HIGHEST

On-Ofl Cootrollerf limit

High

Law

(Vapor Heating Systems)

Vacuuml Prl$Swe

l404

U,,,,

PA404A High LSnit PA404B Fan Control L4079 (High Limits only)

l408 l508

l411

1 spst mercury a

1 spdt mercury

1 spst snap-acting

1 Of 2 lfpat

!tllap-acling

1 spst mercury

1 spdl mercury

1 spst

-"'"

, ,

2 \:115 psi 0.5 \:I 9 pSI

2 \:I 15 psi

o to '8 ozlsq in (0 to ,

p!t~

22 ill Hgl:!

vacuum b

35 psi pressure

7

3

22 ill Hgb vacuum to

35 psi pressure

o b 15 psi

10 \:I 300 '"

Gas/Air Pressure Swi10h

0637 C645A B C645C.O (Air only)

1 spst mercury

1 spdt mercUl)' 1or2spm mercury

1 spdt mercury

1 spst snap-acting

1 spdt snap-acting

In wee

10 \:I 100 psi

otm potentiometer ftlr proportionirJ9 control

e Inches at water column; 1 in we 0.036 psi = 0.249 koPEI

231

A temperature contrOller is 8 device which acts indi­

rectly 10 regulate the temperature 01 air or liquids A sens­

ing elame"U responds 10 temperature changes and

1hrOl./ttl a diaphragm or bellows and mechanical linkage,

actuates a switch or potentiometer 10 keep the lempera­

ture within predetermined limits

Temperature controllers we commonly used In flame safeguard systems to reQJlale the temperature 011iquids

in toilers ()( lOtorage tanks, and for fuel chanceoV9I (switching from crle luello another when the temperature rises or falls)

TEMPERATURE SENSING E L E M E N T S : - - - ­

The temperalure conlrolJels used In flame sakQ;a{d

applicatiOl'l$ hSWil silMr vapor-pressure or liquid-filled

aenslng elemenls Various types of these elements are

s.rnmarized in , Table 11/ at the end of lhis discussion

VAPOR·PRESSURE ELEMENTS

A vapor-pressure temperature sensing element c0n­

sists 01 a remote bulb connected \0 a ~in the c0n­

troller by a ~jl1alY tubing These meta! ~ts

contain a volatile liquid and the vapor from it

When a volatile IQJId is c.Ql1fiQed, a portion of the liQ.Jid

is ~.iven offas a vapor (jusl as steam is driven off by boiling

wale~ until a limiling pressure is developed This pressure

Is adirect function of the t~rature of the liQ.Jld, particu­

larly af thElliqJid SUrface (the dividing lina between the liq­

uid and the VajXlrj Changes of temperature thus result in

corresponding changes ot pressure This relationship is

shown in Fig 26

T[""l:R~TURE

FIG 26-TEMPERATURE-PRESSUAE RELATION­

SHIP IN A TYPICAL VAPOR-PRESSURE

TEMPERATURE SENSING ELEMENT,

The vapor pressure increas9S wilh 'BI1l'9!alure, as

shown by the curve in Fig 26, until the fadeout tempera,

uid has Vl'tpOrized so lllere is no liQUid letl in tile s','Slem A

further rise in temperature prOduces a more gradual rise in

pressure conforming to the gas laws The contro'ler must

be desi"n91::fscdhe 1adEloul temperature will be higher

lhan the maximum operating temperature

For reliable operation, the liquid surface mLJ!;I always

be within the bulb As long as the liQ.Jid surface occurs in

the bulb, the bellows and capillary may be filled with either

liq.JJd or vapor wllhout aNecling the control 0' lerrperature

al the bulb Qlangas in bellows or capillary temperature

will only cause condensalion or evajXlratlon Of a lillie iiquid

in the bulb, with a ~ligi!;!'e change Of pressure in the system

Vapor-pressure lemperature sensing elemems have a very smalltime lag, and temperature variations along the capillary and bellows (within the r9Slrlclions for Jow and

high t~ratul'8 elemenls, which will be described late~

cb not affect the plecise control 01 the remote bulb

eleme"t

There are 3 types or remote bulb vajXlr-pressure ele­ments, ~ng on the bulb-to-bellows tel'Tl;:JElrature re­lalionship They differ in lhe size of the bultJ and in thai relative amounl 01 liquid contained in the bulb and in the bellows

LOW TEMPERATURE ELEMENT (FIG 27)

A low l~aluree/el"l'l6l1t /also called a "/imiled fill"

or "ladeout~ element! is designed to operate with the bu'b always colder than the bellows and capillary The system

contains a limited amounl of liquid so lhat fa,jeoul will 0:'

cur al a temperature not much higher than the maximu'T1 operating tefTl)erature Therefore the bellows and capil­lary are always filled with vapor As the lemperature attha bulb rises, a little more vapor will be prOduced in the bUltJ, increasing the p'essure at the bellows As lhe tefTl)eratu~e

falls, a litlle more liQ.Jid will condense in the bulb and the pressure will decrease

Condensalion occurs first al the COldest paint in the system Therefore, the bulb must always be colder t1-an lhe bellows and capiUal'\' If lhe lemperalure at any ~inl alone the capillary or al the bellows falls below the lem­

232

perature at the bulb, the liQUid surface will shift to the cold

spot outside the bulb and Il'1e bulb will lose control

As not much liQUid is required, (he bulb is small-1/2

loC:h112.7 milllmetres, or mm] diameter by 4 inches [102

mmllong is a common size The elevation 01 the bulb with

rasped 10 lhe bellows is not critical; the prassure head (j&

veloped by the weight 01 Il'1e vapor in the capillary and bel­

lOWS Is negligible

minus 130 F 10 minus 70 F [minus 90 C (0 minus 57 q at

one eJ(lreme~ar1dplus 65 F 10 plus 95 F [plus 18.5 Ctoplus

35-C] al the'other.'Themaximumsafe temperature,l.e., the

bulb temperature at which lhe maximum safe bellows

pressure is reached, is generally much higher than the op­

erallng range of lhe controller This is beCause fadeout oc­

curs Just above Ihe maximum operallng temperature, so

llote pressure increases much more slowly at higher tem­

~~~'LJ!QS (see the gas curve in Fig 25)

HIGH TEMPERATURE ELEMENT (FIG 28)

Ahigh temperature element is desigIed to q:.erate with

lhe bulb always warmer than the bellows and capillary

This system contains enough liquid so that, at the highest

operating temperature, the bellows and capillary will al­

ways be tWed with liquid and the bulb wlll contain some liq­

uid As the temperature at the bulb rises, more vapor will

be produced In the bulb, il]creasing the pressure on the

liqUid surface and also at the bellows As the temperature

As the bulb must cOnlaln only enough liquid to ensure

that there will be a small vapor space present at the lowest

operating temperature and a little liqJid present at the

hil1'esl q:.erating temperature, the bulb Is small-1f2 inch

(12.7 mm] diameter by 4 Inches j1021TVTl]long is a com­

mon size Preferably, the bulb shOlJId be at about the

same elevaliooasthe bellows It there is a large difference

in elevation, the pressure head developed by the weight 01

;/?::::t-l,.Imlts><C·oot,ollers:;{;:'::K,:<:::'~ij#'~llh't'~'r1(,)Cks the liquid In the capillary and bellows would be ad:Iad \0 or subtracted tram the vapor pressure and might cause Im­prc:per calibration at the controller,

Typical extreme scale ranges tor high temperature ala­menls are plus 75 F 10 200 F [plus 24 C to 93 CJ and plus

510 F to 700 F [plus 266 C to 371 C] The maximum safe bulb temperature, Which at high temperatures also in· cludes the safe temperature of the metal or the melling point of the solder, Is generally not much higher than the top of the c:perating range ot the contrOller

CROSS-AMBIENT ELEMENT (FIG 29)

A cross-ambient element is so-called because It Is (j&

signed to operate with the bulb temperalure either higler

or lower than the aJrt)ient temperature (at the controller and capillary) The system contains enou~ liqJid so that

at a temperature somewhal higher than the hig,est oper ating temperature, the liq.Jid will 1111 the bellows and c:apll· lary wilh a litlle ll!ttJl'£S,l: tor the bulb

When the temperature at the bulb rises aoove the arrbi­ent temperature, more IlqJid will condense In the colder bellows and capillary More vapor will be present in the bulb, increasing the pressure on lhe liqJid surface and also at the bellows When the lamperature at the bulb falls below the ambient tempera!ure, more liquid will condense

in the colder bUlb and the vapor pressure will decrease Bolh ot these conditions are shown in Fig 29

at the bulb falls, more liquid Will condense in the bulb and

the vapor pressure will decrease

The bulb must always be warmer than the bellows and

capillary It the temperature at any point along the capillary

or at the bellows rises higher than the temperature ot the

bulb, the liQUid surface will form OIJtslde the bulb and the

bulb will lose control

FIG 28-DIAGRAM OF A HIGH TEMPERATURE

(uS> VAPO" ''* BULB)

FIG 29-DIAGRAM OF A CROSS-AMBIENT,

VAPOR-PRESSURE TEMPERATURE SENSING ELEMENT

The terrperalure relationship between the bulb and the bellows is not crillc:al as ills for the low and hi~ t~ra­ture elements Even if part of the system is wanner than the bulb and filled with vapor • while the remainder is colder

71-97558-1

than the bulb andtilled with liquid, there will slill be a liquid

surface in the bulb and the bulb will continue to conHol

As there Is enoug-t liquid in lhesystem to fill the bellows

and ~Ill;:l.ry, and lhebulb must contain all of this liquid at

the towest ~raling lemperalure, the bulO must be

large-11/l6 inch 117.5 mm] diameter by 14-1/2 inches

{368 mm]long Is a common size lflhe bulb temperalure

will sometimes be warmer than the ani:lient temperature

causing the bellows ani::! capillary to be filled with liquid,

the bulb should be at aboulthe same elevation as the bel·

lows Olherwise,' the grassure !:!~d devel~ by !he

weight of the liquid in lhe capillary and bellows would be

added to or subtracted from lhe vap:::l( pressure This

would make the device unslable dJe to shifting of the con­

Irol p:>int, and would cause irT';:lr~r calibration of lhe con­

- troller If it is known thatlhe bulb will always be colder than

the ambient temperature, the elevation is not critical

Typical scale ranges for cross-ambient elements are

minus 25 F to 0 F [minus 32 C to minus 18 C] at one ex­

treme, and plus 40 F to 210 F !plus 4.5 C to 99 C] at fhe

other The maximum safe bulb temperature is generally

nol much higher than the tcp o1lhe ~rating ral1QEl

L1aUID·FILLED ELEMENTS

The basic IiquicHUed temperature sensinQ elemenl

(Fig 30) consists 01 a remole bulb, a ~werhead consist·

ing of a diaphragm and case, and a connectinQ capillary

The entire element is completely 1iIIed wilh a temperature

expansive liqUid Temperature changes al the bulb are

transferred lhrolJQh the bulb wall (usually cq:per) to the

liqUid The volume of the liquid eilher expands or con·

tracts, causirlQ resultinQ molion 01 the diaphragm Aslhe

oPeration is hydraulic the force at the diaphragm is '!fP~e­

ciable This force is transferred by mechanical linkage to a

switch or ~lentiomeler in the controller

FIG 30- DIAGRAM OF A TYPICAL LIQUID­

FillED TEMPERATURE SENSING

ELEMENT

The capillary lor a remote bulb element is made of cop­

per, monel, or stainless steel, and cantle any length up 10

about 30 feet [9 metres]: the most common lenglhs are 5,

20, and 30 feet [1.5, 6, and 9 metres] Some controllers do

not have remote bulbs In Ihese direct-mounted control·

lers, lhe capillary is very short and internal; only the bulO itself proJecfs OUI trcm the case (Fig 31)

A standard bulb is about 3{8 inch [9.5 mm] or l/Z inch [12.7 mm] in diameler, and from 2106 inches [50 to 150 mm] long It can be used in either air or liquids Fast­response and averaginQ elements (Fig 32) are also avail­able 10r remote mounhnQ in air ducts

5TANOARO REMOTE BULB

A fasl-response element is in the form of a lightly coiled capillary About 6 feet I 1.8 melres] of capillary is coiled into an elemenl about 1-1/2 inches [38 mm] in diameter by about 5 inches [127 mm]long The surface area 10 volume ratio is about 7 times greater than that or a slandard bulb,

so its response time is about 7 times faster

AA averaginQ element (Fig 33) is althe end of about 10 feet {3 metres] of standard capillary, and Is similar to the capillary except thai it has a larger bore in order to hold the same amount 01 liquid as a standard bulb It is usually

234

about 1/8 inch {3,2 mmj in diameter by about 12to 20 feet

[3.7 to 6 meres] long An averaging elament is usually

wound back and tanh across Ille ducl It is distributed

-evenly over the cross section ollhe duct to oblain the aver­

agE! temperature in the duct

The commercial type temperature controllers used in

f,'ame safeguard applications have elements tllat are CaT!­

manly filledwilh hydrocarbon liquids, SUCh as toluElfle, sili­

cone, or alkazine The ~HiC~!lt of ekpansion of these

liquids resu,lls in a motion-temperalure relationship that is

not too linear, This nonlinear eHect is minimized by selecl­

ing a narrow temperature range whiCh awroaches linearity, or by calibrating the set point of the controller 10

match the nonlinear properties of the liquid

Typical operating ranges for coni rollers with li(J.Iid­IiIled elements are 0 F to 100 F [minus 18 C to plus 38 C] at

one extreme and 160 F to 260 F [71 C to 127 C] al the other The maximum sate bulb temperature ,'s Ihe point at which the diaphragm is extended as fat as it can I):l with­out taking a permanent sel This lemperature is not much higher than the top of the operating range, and should never be exceeded

Since the liqUid is homogeneoos and fills the capillary and powerhead as weiI' as the bulb, temperature changes

at the capillary or al lhe powerhaad caUSe errors These

errors are minimized by making the volume in the capillary and powerhead as small as possible, by usinga liquid with

a low coefficient of expansion, and by providing arrtlient­temperature compensation This compensation is usually

in the form of a bime(allic device in the powerhead liquid-filled elements provide power and rapid re­sponse, and are not aHected by dHerences in elevation between Ihe bulb and Ihe controiler They can be used at any ~, and can control at temperatures above, ba­

low, or awroximately the same as Ihe temperature at the case of the controller They we generally less expensive lhan vapor-pressure elements, althOugh they may t'()t be

as precise

LOCATION AND M O U N T I N G - - - ­

Both the controller case and Ihe sensing element must

be located where the arrt>ient temperature will not ekceed

lhe maximum aiTCIient operating temperature speCified

for each !The specified maximum temperature for the

case is different than that for the sensing element)

The case can be mounted in any convenient posilion

on a flat surface, such as a wall or panel If the mounting

surface is hot or cold, the case should be insulated lrom it

tJy insulation maleria! (such as a wooden bOard), or offset

1.0 allow a spa e for air circulation Mounting hales or lugs

are provided on lhe back at lhe case

The sansing element should be located where it is ell­

posed Co the average tf3tl'lP9lalure or the cootrollad me­

dium The temperature and elevation rules shOllld be

obse~ed for vapor-plessure elements (see Table 111)

A few temperalure controllers are direcH'nounted, but

most models have long capillaries fO( remote mounting 01

lhe sensing element r remota bulb· models) Depending

on the application of the contrOller, the sensing element

may be mounted in an immersion well, compression fit­

ling, capillary holder, bulb holder, or bulb shield AA aver­

aging element is usually mOllnled inside an air duct using

perforated strap iron or Clips Usual applications, pur­

poses, and limitations of various mounting means are

summarized in Table IV Mounting means are shown in

Figs 34 through 45

Soma controllers have a very short capillary lhal cbes , t'()1 ektend beyond the case; only the sensing elemenl (bulb) sticks out

These models- are for mounting directly to boilers or storage tanks Horizontal models are available for a tap­

ping on lhe side of the boiler or lank, and verocaJ mcdels

are available for a lapping on top Some models include an immersion well and Ofhers incll ll:E a compression Ming REMOTE BULB TEMPERATURE

CONTROLLERS Mosl temperature controllers have long capillaries (~

10 30 feet [9 metresjlongl so the sensing elament can be mounted at a distance from the controller, The !EWlQlh of the capillary may limit the choice of location Sharp bends

or Wnks in the capillary could serious/)' affect th8 operation

or cafibrarton of the controller: ttMy should be cafBfully avoidfU'J All excess capillary shOuld be carefully coiled

and left directly beneath or beside the canlralle(

MOUNTING IN A BOILER OR STORAGE TANK 1lle manufacturer of a boiter or storage tank usually provides a tapping for Insertion 01 the sensing element Follow {he manufacturer's instructions If available If the boiler or tank is fiiled, drain II until the level 01 the fiQ lid Is

J{ ·PI'l'lIt~tC:.i:mtroll~lS ::'i:

Rig !:?}'~ctJn\~rlC)!?Il.:~i/" ';,JB;"}

TABLE ill-TEMPERATURE SENSING ELEMENTS

','

TYPICAL SCALE RANGES

MAXIMUM SAFE BULB TEMPERATURE

Vapor·

Pressure

Low Temperature (bUlb co/de!"

ttlan behows) High Temperature (bult wwmer

than bellows)

1/2114 in

112.7 II l02lmll 1t211 4 in

]12.7 11102 n-wn)

Nat critical,

,Same as belbw~,

-130 to -70 F

+75to200F 1+24togsCj

+65to95F {+ 18.5 to 35 CJ

+510 to 700 F [+26Sb37' CJ

MUCh hlgl'oer than operating range, Not much higher than top of operating renge

(bulb can be CrOs.s·Ambient tither

COIdar Of warmer ttlar belb )

11/18 II 14·1/2 In, {17.5K368m-nl

Same as ballo'oYs

iI bL-llb wi" be

WlV/r>er 1t111.n ambienl a: other

wise rot critical

-25bOF [-32 b -18 q [+<4.5 to gg Cj +40to210F

NOI much higher han lop 01 operating range

,

Filled

Liqlid-Standard Bulb Fast-RespoNe 'Ioment (air ducts) Avel'ag'ng Element

Nol much h'lgher than bp of operating ranga

TABLE IV -METHODS OF MOUNTING TEMPERATURE SENSING ELEMENTS MOUNT1NG

MEANS ELEMENT SENSING FfG{S)

COH·

TPOLLEO MEDIUM

- pro\llCt eltlment from mechanical or chemical damagl;l

moval of element

- More than doubles response time

- Well must be 01 pr6pDr siZ':' to frt snugly

5 B~'

ComprGSSion Fitting

DirE!ct m::Junled Bulb

- Form a positive seal

- Bulb must not be

100 large b support Fast·response

EI9I"I1ent "

"'"

Holder

large Remote Bulb

42

'" ~r ducts

- SBme as capillary IXIlder

- For larger bulbs (such liS c~-amb~

ent, vapor-pressure elements)

- Requires large IXIle in duct wall

Bulb SIieId R8'rote Bulb 45 ", -Dual fuel change­0tJnm0r nnmting

"""'

- Au1c:matic reset uSing dual bulb t9mperlllJJre con-­

"""",,

- Protect bulb While exposing n to Itle.alr

- Requlrell hole in wall 01 building,

236

below the tawing In the boiler or tank Remove the plug

from the tawing, and screw the spud of the immersion

-WQUor compression lilting Inlo the lapping A redUced tlt­

tlng may be necessary to adapt lhe spud 10 the tawing

Make sure lhe well or filUng Is screwed in tightly lopre~ent

leakage Il"IStalied Ihe sensing bulb and controller Then

refill the boiler or lq.nk Do not tIY to tightan the well orfitting

in the tapping by turning the controller

USE OF AN IMMERSION WEll (FIGS 34 AND 35)

- An immersion well (~rable well) is used to protect

Ihe sensing elEll'T'l8nt (in Ihis case, the bulb) from mechani­

calor chemical damage, and to permit easy remo~al of the

element from the liquid without haVing to drain the boiler or

tank In addition, it pro~ides a lighter filling than other

rf,'ounlingmethods An immersion walt is very desirable for

mounling the element in an agitated liqUid

The immersion well must be mounted where it is always

exp::lsed to the circulation of the liqUid under control, but it

must never be localed close to a hot or cold inlel or steam

coil

The use of an immersion well more than doubles tMe re­

sponse time compared to that for a bare bulb Therefore,

the weI( mustfl! the bulb snugly II may be desirable to !Ill

the space between the bulb and Ihe well with a haat-<::on'

ductive comp::lund The use of a heat-conducti~e grease

will reduce the resp::lnse lime 10 aboul 1-1/2 times Ihat for

a bare bulb

USE OF A BULB COMPRESSION FITTING

(FIGS 36 AND 37)

A bulb compression filling is LJS.8d to form a positi~e

seal althe p::linl where the sensing bulb is inserted into the

controlled liquid It Is Llsed in awlications where lhe bulb

can be immersed directly in the liquid without danger 01

mechanical or chemiCal damage The COOlJression fitling

is Qanerall'( Selected tO,be,the same malerial as the bulb A

remote bulb must have a nange for the filling 10 hold

USE OF A CAPILLARY COMPRESSION FITTING (FIG 38)

If the remote bulb doEl6 not have a flange, a capiilary

~ressJon tilling can be used to form a fXlSlllve seal In awllcallons where the bulb can be Immersed directly In the liquid without danger of mechanical or chemical

damage

RlAO JAW510 "T

O~." COCLAR ON SPUO

Of "'Hl SCREWORIVER

I><SULAno Of 80lcER

WAlLOfaOllEROR STORAGE u

INSU"AT"~ Oe-H' -,,,SERno OEPTH n,

& RlOUClR F,rrl"G MAY 8t NECESSARy TO AO T?VO T<l u ,

FIG 35- MOUNTING A REMOTE BULB IN AN

IMMERSION WELL

CONTROLl.ER CASE

&

IMMERSION l'I'ELL,&

SPUO SCREWS INlO lAPPING IN ~