Document x54mr1j8Vj30Jz1waLaJaYrE

,1. f; ' I !: ; 'J By selecting recommended automatic-lighting devices and sequences you (eel sure you're getting'; adequate protection, reliable operation for today'j highly popular unattended packaged boilers MAIN OAS SAFETY SHUTOFF VALVE Avoid- tiling an auiomaite-openlng, autonulie-cloaiog safety shuioff valve with tho replaceablctAsme rod and pilot unit shown hove. Reason is that lighier-lotih ftime-conticting rod within the housing would automatically admit unbunted gas. SAMPUNO COCK Approved sampling cock (No. 2, above) for leakage test of main safety shutoff valve locoicd downstream of safety shutoff. Connected with V4**n. 00 copper tubing. COMBUSTION SAFEOUARD Contact 1 is safe-ssarl relay contact, ond most be closed If safety shuioff valves are to open. After start pushbutton is pushed and a torch Is inserted to light the pilot, pilot flame contacts the flame rod causing flame relay contacts 2 end 3 to close, end com* pleling circuit to pilot safety ahutof! valve and main safety ehuioff valve. After atari pushbutton is released and as long as pilot flame eonlacta flame rod. pilot safety shuioff valve remains open. Main safety shuioff valve must be opened manually. Flame relay con* taels 2 and 3 open on flemc failure. See No. 3, drawing, right. FLAME ROD } located so pilot flame contacts it only where pilot will reliably? Ignite the mein burner. No. 4, in the drawing, left, above. '* .MODULATING MOTOR '' This motor, No. 5, above, controlled by a modulating presstut: witch, adjusts the firing rate in response to steam demand by` means of linkages operating gas throttling valve and* burner cb'< louvers, fn closing, the throttling valve travel is stopped at tha > least opening that produces a stable flame at the .main bump unit. If ateam demand Is still too small at this firing rate to ksb; the rise in boiler ateam pressure, the opcrailng-preuure-llali ' switch opens, closing the operating*{rresaure*ftmit control vibo,- . which turns off the main burner unit. First drop In boiler sicta'i pressure automatically opens the opereting*presaure*limlt control,, valve, and a further drop cause* the throttling valve to begla J opening. Drawing, right, above, shows wiring. i Oil SAFETY SHUTOFF VALVE ' Automatic-opening, automatic-closing approved for use srbh.' heavy oil. See drawing! facing page. Remember, heavier afl;j Dead'definite flame stabilisation before you're sure ihey're safe. Combustion safeguard, No. 2, above. Contecu I end 2 through action of motor-driven earns or thermal warp switches open a call for best by the operaiing-pressure-limli switch, atari the boroer motor (not shown), and ignite the gsa pilot. Contact j |ht lafe^tart telsy contact, must close If you are io gel ignition ind open safety shutoff valves. When gas-pilot flame contacts the fitre rod, the flirao-relay contacts 4 and S cloe, completing lbs elrcoil to the oil safely ohulofl valve provided there is proper primary air pressure Aflcr the nlsl-for-ignltion period, contacts I tad I open to shut off the gas pilot and require ihe.phetohcad t sight the ofl flame or shut off the oil and burner motor by open* lag contacts 4 and 5. Flame-relay contact* 4 and 5 open on flame (itfare. See wiring diagram, right, above, Flame rod. No. 3, is located ro pilot flame contacts It only vherb pilot reliably ignite* oil. OIM*mporoluro Interlock No. 4 is set so burner cannot peN' ale,unless oil is at temperature recommended by burner manu facturer. Electric ell heeler No. S should be located in the piping oa close to oil-burner spinner cup as possible. Titus heated oil is available at the spinner cup prompily after safely shutoff valve opens, thereby avoiding pos ihle ignition troubles. Modulating motor No. 6 adjusts firing rato to ateam demand by linkages operating the oil throttling valve and primary and secondary air damper*. Id closing the throttling valve, travel la stopped at the least opening that produces a stable oil flams. 11 team demand is still loo small at this firing rata to hall the rise in boiler steam pressure, the operaling-pressure-limit switch opens its contacts. This causes, the oil safety *hutsff valve to eloao and the burner motor to slop. The first drop (n boiler steam pres sure closes ihe.opersling-pressure-Hmit switch and starts the light- ing-ol! cycle. Modulating motor also give* low-fire lighting. Such a motor either has a spring return to the low-fire position upon power interruption or requires electrics! power to move from high- to (Fiw-fire position. Where * motor is of the power-return type rnttry switch mounted on the motor shaft and wired in the safety circuit should be provided to Insure that motor is in low-fire potilinn before ignition of pilot or main burner can be attempted. Tried and Tested Automatic Combustion Controls Reduce Packaged Boiler Ills ^Dcspitb state and local government's insistence on safeguards for automat ic-fired boilers, these units accounted for 13% of The 1936-1943 losses from boiler-furnace explosions with all fuels. As a class these boilers run smaller than manual-lighted boilers (averaging below 10,000 lb per hr for units sur veyed) and are not constantly attended. They usually have, though, automatic combustion control ol a tort that varies the firing rate in response to steam demand. They can be further general ized aa having one burner, combustion air or forced-draft fans, and occasion ally induced-draft fans. But protection of these units has hacome unduly complicated. It has suf fered from an accelerated development of many different pilots, automatic light ing sequences and nonapproved methods ol application to boilers. Whet should be a straightforward job becomes con fused and -proves the most dangerous element in operating these boilers. Be cause of this confusion and a trend toward larger automatie-ifghted boilers, the Factory Mutual Engineering Dlv* has put togather recommended methods 'Prearuliaf Putt iu Cti- and OH- Pirvit Baiirtt, Pnctory Miritifll Rnsti DU. IM Hl*h St. Boiton )J. Main, (see summary above) for proteeliaij these units against Important fuel-ex*.I plosiop liaaards. There are actually only two danger periods where boiler explosions mi? occur: (1) during , lighting-off (2) while burners are firing. First period occurs with ignition dangerous accumulations of unburo*di{ fuel or flammable products of incoo*.' plete combustion left 2n the (urntc* chamber from previous operation. I* has been responsible for about 60% ol. the total explosions. Second danger period--while bum** are firing--touches ofl explosions kf 97 ENGINEERIN'} AND MANAGEMENT SECTION POWH Retting afire unburned fuel accumulated after a flame failure or Igniting of flwnmable products left behind from in complete combustion. 'Ughtlnp-Off Period. An approved combustion safeguard assures safe lightag-off. It does it this way. The snfetuard delects flame failure and, teamed with program relays, limits amount of "nburned fuel discharged to the furnace. .This action sequence is known oa the 'tna!.for,j87>|,|oa period. Stack switches end other unapproved safeguards prove co.ilow. They permk too long a trialoHgnhion time and hence Loo heavy ooild-up of explosive materials. They may bo likened to a eorelees firemen who turns on the main fuel, then waits a minute or two before bothering to check if the main flame has lighted. In fact, approved combustion safe guards ore even more alert than the most diligent fireman. They can sense the main flame promptly and, what's more, prove9 thot o pilot flame is present before ever permitting the main fuel valve to open. With such absolute as surance that an ignition source is present you can deaign for a longer triel-for-lgnition period. This ability ex tends the automatic lighting feature to *8s* ''DvSnlltuM*' ofl pflga 14. heavy oil burner* that require definite flame stabilization before you're sure they'll stay lit. Firing Period. Once the burner is firing, your explosion danger drops ofl. Only a third of the total explosions reported occurred during the period. And then two out of three happened because of dangerous accumulations of unburned fuel following a previous flame failure. Flammable products of incomplete combustion accounted tor the remainder. Here again, approved combustion safeguards minimize (he risks. Where unburned fuel, for example, aceumu- ,(**V*AT CNOtNEERINO ANQ MANAGEMENT SECTION 93