Document DG9z5O66nJDgxdo4mVaGaOLMQ

Survey by Notionof Boord of Boiler end Preuure Vessel inpetlor* blames fow*wofr tvl* offs for 38% of reported boiler exploaiom. Yet equipment is well built, engineered so foul) seems to be the user's. Here are some helpful service ftps Low-Water Cutoffs Profit From Can P> Whc* notuns tJtrtooe the usual reaction is to took for operating flaw#1. But they're not slwoy# the c*un. Beek experience indicates there aro four1 major atumbllng blocks that lead to low- pressure can jump rapidly to (Jk safety-valve setting. in January 1952, the National Hoard Bulletin carried the result* of a survey entitled, "Causes of Accident* to FireTub* Boilers In Laundries." The survey water cutoff failures- They are: (1) inadequate range ol control (2\ im proper installation (3) poor operating practices (4) spotty maintenance or complete lock of it. Under this emergency the bvcutoff designed for 50-psi terries itself under double that presun you need it most. Chance* of f (aid the blame (or boiler failures on overheating r burning, 62%, and fuel Inodoquoto'Contrels. Certainly you'd satisfactory low-wster protectise mighty slim. cutoff failure, 38%. These results prompted a flood of expect the average operating man to know and recognise the prime impor fn much the same way ini? report electrical switches on to* failure reporta to the Notional Board. tance of maximum aflowobie operating cutoffs carry loads way above i So much so that the National Board in iti October WS2 Bulletin raise* wo questions: fll Would boiler* be aafet without a fuel cutoff device? (2) Do the records justify safety rulings on fuel cutoffs lor power boilers, such as those adapted by many states, municipalities, provinces, end insurance companies? Actually, the ruling requiring inatal* latioue ol fuel cutoffs on power boilers came about because of (1) the wide ac ceptance of automatic firing (2) boil ers operating with less heating surface and less water storage. All automatical ly bred, htgh-preosura steam boilers limply must have an adequate fuel cut off to protect them against the dangers of low water. Devices on the market that da this job are manufactured by reliable companies, are well-engineered, and should operate satisfactorily. Whot, then, is the trouble? '"Tta* P<* gups K*lp Prwssi fuinu* 8sntwloitt,'* Pewn. Ott t|l>. pressure on a low-water cutoff. Vet he completely overlooks or (ails to check it when he decides on a cutoff. Maximum allowable operating pressure shows on the manufacturer's nameplate, together with the electrical ratings. But many an inspector telle' u* H'a not at all unusual to walk into a boiler room and find the control has been selected on the basis of boiler working pressure, rather than on the basis of maximum allowable operating or design pressure. For some strange reason this short sightedness occur* frequently on boilers where the steam salety valve >* set lor 100 psi or so, hut the boiler operates at 35 to 40 pal. Controls ore those designed and approved lor 50-psi work ing pressure on the grounds that the normsI boiler-operating range lies be low this point As Jong as the pressurelimiting devices Operate--that is, those that start and stop the firing equipment --pressure will always stay below the 50-psi level. But if they fail, boiler Because these switches are safe vice* and net operating elements, loads esn exist for some time * causing breakdown of {she op* of the switch. Yet it's a needless to take. Once again, you'll find the #l ratings stamped on the manofoc nameplate. If a switch U design a 14-hp motor you're asking for l so hook it up to a full 1-hp moto Installation Stops. Over and slK troubles you bring down on youn inadequate controls are the one result from a poor installation sketch above shows * simple Insta where low Cutoff has been in properly. Often inspectors find, the manufacturer has provided 1 openings for J-in. connections, the man has turned around and rt them for %-in. service. True, lb ttol works all right from the star remember, it's still new and If ih* lelt l-ln. connections were correct fUNT OPERATION ANO MAINTENANCE SECTION low-water cutoff. Now and then, you see a small team-flow line tupped, into the water cutoff be sure you report It im mediately. Also notify all boiler-room attendants so no one relies upon the rvfce Vff tar Cutoff tore Hating* must bo lorq* tin )*b a' hood. This taka* 0f (ttem ofmrwSlnp pressor* ofof/kal ratings. stcnm-eqnsliting line. With it you get only a false reading. It stands to reason any connection to other auxiliaries changes the pressure-drop conditions in the piping ond that change carries back to the water glass as well as the low- water Cutoff, Many manufacturers now tie the low- water cutoff right into the water column to reduce required piping and firmly cutoff t a salety device until you're sure it's working properly. White we're on (he subject, inspectors report that operators frequently put In manual controls for their own conven ience. The manual lets the operator keep the burner running for purposes o( fits own even when the cutoff is con tinually calling for turn off. This Is not good operating practice, and you should incfollelien ought to bo rac- position the control and water column close to the boiler. Once again, though, rip out any such wiring that you come rboot fapfero, yet fobs keep rfi wrong pipe slies, tutor* it pays to check that the two openings for the water column ere in use. Con across. Maintenance. High on the list of es sentials for keeping low-water cutoffs S*tt\o*h end so on. sult Paragraph P-322 of the ASME Power Boiler Code for rules covering performing as you want is maintenance Each lime you shut the boiler down for dog PtocUttt naed reviewing, proper installation. complete washing and inspection, don't nti evetfoefc'tha value of rogwdewm, operating cheeks an inti, resetting of odjusiments. Why all the fuss about Installation? Suppose (he low-water cutoff works only a* a safety control end is set to shut off the automatic firing device if tha forget to inspect all piping attached to the low-water cuioff. Further, remove the operating heads and check the in ternal condition of'tRr float bowl. Be ijrfMjw# Programming carrj ny benefits you'd oxpatt it would -jvfaffs. 1*4 that you sehtdufo went of operating heads. water level in the gage glass drops to *4 in. of water. If (he wafer column is positioned too low, the firing equip ment shutoff may be too late. Often the low-water cutoff device does double duty and acre as e pump on-off on the tookoul for any scale or sediment build up here. Scale should never build up. II U does, make sure you instruct your operators on blowdown procedures for daily use. While about it, run a check of the blowoff velvet to te thu control, too. Then the operating point for the pump-control duty Is set higher they operate properly or whether any `follow through? Experience tha J-in. connections provide the r,equalisation, as well ss reduce than the minimum *4-in. point for safety. Actually, the safety and pump-control features should be planned for separate action. In this wav the fuel cutoff still serves as a final safety backup for pump parts need replacing. The above procedure holds especially true lot those controls serving the double duty of pump controller and Jowwnter cutoff. Remember, this class of control operates continuously and sncei of trouble Irom sludge op. Whatever you do, toko adtig* of the fuel-site connections the ;ipm*nt carries. uote la the sketch that the safety qo) connects directly to the water fan.'Also, the connections ate at' ' si possible and in full tile- Next, 'II see that the all-important equal- connections have gone in. The two actions between water column and (eildte. * Operating Practices. Like olmost every ruber boiler auxiliary, the lowwater cutoff safety feature can fail miserably under poor operation. All that needs to he done is to blow down the control at lean once a day. ThU removes any loose sediment that ac cumulates in the eoualiw connections or the float howl. As a matter of fact, most manufacturers recommend a blow performs a vital function In boiler operations. Not only does it guard against the dangers of low water, but ft also maintains the proper water line. A typical boiler equipped with such a combination safety control, running at peak load for at least eight hours and probably more a day, he# this particular control working practically continuous ly throughout the run. Wear is bound to be heavy, md serving as both an r;si reproduce the water line as it ttds wfthtn the boiler. Any alteration this piping or inclusion of some ~tni* gimmick in the connection to Viter eolotrtn can upset the position ' the. water line in the column and down an the nomeplate. Freauently Ho'tcr inspectors report tampering with the adjustments on the cutoff to chance operating levels beyond the recommended limits. You can *et them so for out of adjustment that the operating and safety control its condi tion is vital to good boiler operation. U oeem# shortsighted preventive main tenance to allow so vitl a boiler ele ment to run to failure. A program could be readily set up to remove the operat d to a false reading in the water Check through iheie poinis when you at in a (ew-water cutoff. See tbot the sir-column setting agrees with the ,'iler manufacturer's recommendations, est, cheek that the lowest visible port *f ihs water plo* meets with ASME leiler Code requirements. Finally, be . eniin the piping connections to the lon-waier cutoff insures o true roprokion of boiler-water level. Remember, make no oihei ceituccIans to the water aide of the water cutoff cen't operate. A neriodlc rheck of the r.utnff under ntieralin* eo-v/t-i-ons show* this un. You ran do it easily enan*b bv vnMnx off th feedwater *>mnlv under o minimum hdW load. Thr* let the water level dmn to *hn cutoff position bv normel vetwirtirtn of *ram In the ho'ler. Ynn'll find it smart. oo*r#tion to do this about. once a month. S^ouM the Cutoff fall to revnond. v*m haw*, time to take -rtrafivr t*'<s. This Oiwrat'C* check cvwi1j jin' "itlv lmi!r.i*tr adiuktnicnis n'>il aceunvdutUm*. even ing head of a safety device, (ay the first or second time you shut a boiler down, for general maintenance or in spection. Replace it with a brand new heed end return the old to the factory for rebuilding. When it returns you have s spare head for yur next boiler shutdown. A program of periodic re* nlacement of the operating head, once a year of everv two years, would make preventive maintenance a paying ooliev. ft low-water cutoffs get the benefit of this 4-point planning, look for a shorn dr*n* in boiler explosions due to fl Womn and tuw-water cuioff, nr to rite l(am s'uU of the water columns and the .faulty mw.rotinn of relnvs. Once you do uncover a faulty low- cutoff failures In plants everywhere.