Comprehesive Boiler Manual Jan 2019

3) Pop-Off Valve
4) OS&Y
Safety Pop Off /
Pressure Relief Valves
Steam venting during
Relief Valve test
Only manufacture’s
rep.’s can work on
safety pop off valves.
Accumulation Test determines if safety
valve capacity is large enough to
protect boiler. All steam outlets are
shut and firing rate is increased to
maximum. Safety valve should relieve
all excess pressure.
Hydrostatic Test determines strength of parts or welds on
new and repaired boilers. Safety valves are gagged with a
clamp or removed and replaced with plugs. Boiler is not
fired. Water pressure is then pumped up 1½ times safety
valve setting. Check for leaks.
2 pop-offs are required for
boilers when heating surface
area > 500 ft 2
When checking safety valves manually, boiler psi
should be at least 75% of popping pressure.
75% of 210 psig = 158 psig
Steam line stop valves are typically OS&Y
(Outside Screw & Yoke a.k.a. Outside Stem and Yoke)
Drip legs relieve condensate on main
steam line if line is down.
Pop off openings inside steam drum
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