Boiler Auxiliaries, Fittings, and Accessories
Core concepts
Code-required fittings protect the pressure vessel: safety valve(s), pressure gauge with siphon and three-way cock, water column and gauge glass with try cocks, low-water fuel cutoff, main steam stop valve, nonreturn valve, feedwater stop and check valves, bottom blowdown valves, and the nameplate. Safety valves mount directly and upright on the boiler or drum with no shutoff valve between valve and boiler, and are set at or below MAWP. Power boiler safety valves are sized so pressure cannot rise more than 10% above MAWP at full firing.
Accessories support operation rather than protect the vessel: feedwater pumps, FD and ID fans, air preheater, economizer, superheater and attemperator, burners, soot blowers, deaerator, and water-treatment equipment.
Gauge glass practice: in normal service both isolation valves are open and the drain closed; blow the glass down on schedule to prove both connections are clear.
Traps
Be ready to separate fitting from accessory, to spot a shutoff valve illegally installed under a safety valve, and to catch the wrong blowdown valve being used.
Worked example
A boiler with MAWP 150 psig and valves set at 150 psig may reach about 165 psig at full accumulated capacity. The 10% limit is applied to MAWP, so a valve set at 145 psig still must keep pressure at or below 165 psig.