Boiler Fittings, Appurtenances, and Controls
The hardware the examiner expects you to know
Every boiler carries a set of required fittings: the safety valve (or safety relief valve on hot-water units), the water gauge glass with try cocks, the pressure gauge with a siphon and three-way cock, low-water fuel cutoffs, feedwater check and stop valves, main steam stop valve, bottom and surface blowdown valves, a water column, and the nameplate. Automatically fired boilers add flame safeguards, operating and high-limit controls, and feedwater regulators.
Each fitting has a testing routine. Gauge glasses are blown down to prove both connections are clear; try cocks confirm the glass; safety valves are lifted with the try lever at reduced pressure to confirm they open and reseat, while the official set pressure is verified by the valve's tag and a bench or steam test.
Traps
- No valve of any kind may be placed between the boiler and its safety valve, and the valve must be sized to pass all the steam the boiler can generate.
- A pressure gauge siphon protects the gauge from live steam; removing it is a defect question waiting to happen.
- Try cocks are a backup, not a replacement, for a working gauge glass.
- A low-water cutoff that has been bypassed, or one that does not blow down clean, is defective even if the boiler runs fine.
Rule of thumb
ASME Section I limits pressure accumulation to 6% above the safety valve set pressure, and the set pressure may never exceed the maximum allowable working pressure stamped on the nameplate.