Boiler Fittings, Accessories, and Controls
Fittings are what the operator actually touches every shift, so exam items tend to be practical: what is required, where it is mounted, and what a false reading looks like.
Required fittings to know
- Safety valves. Sized so total relieving capacity keeps pressure from rising more than 6 percent above the highest set pressure in Section I service at full firing rate. Nothing may be installed between the boiler and its safety valve.
- Water level indicators. Gauge glass plus try cocks (or two independent glasses), with the lowest visible reading safely above the lowest permissible water level. Blow the glass through every shift; a partly closed isolation valve gives a false level.
- Water column. Slows level surge and carries the low-water cutoff and gauge glass tappings; keep it clean and blown down.
- Pressure gauge with siphon (steam) and gauge cock or three-way valve so it can be removed and zero-checked.
- Feedwater piping: check valve plus stop valve, arranged so the check valve protects the boiler from backflow.
- Bottom blowdown: two valves in series for most power boilers (slow-opening nearest the boiler with a quick-opening valve downstream), or a single valve only in the narrow low-pressure/small-heating-surface case the code allows.
- Low-water fuel cutoff, high-pressure limit, flame safeguard, steam traps, air cocks.
Traps
Questions blur safety valve with relief valve, or show a shutoff valve between boiler and safety valve. Another favorite: the gauge glass shows normal level while the water column is plugged, so the boiler is actually low.
Worked rule
If a 100,000 lb/hr boiler carries three safety valves set at 145, 150 and 150 psig, the accumulation limit applies to 150 psig: total pressure must stay below about 159 psig with all valves discharging at maximum firing rate.