Pressure relief valve

Heating · Heat Exchangers · printed page 143 (PDF page 144)

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Book index entries

Pressure Relief Valves Pressure Relief Valve – on Boilers

Text in the illustration

note: mechanism simplified for clarity
spring
manual relief lever
to drain
poppet valve
pressure less than valve rating
pressure greater than valve rating (or manual override)
pressure relief valves come with specific pressure ratings (e.g. 30 psi for most boilers)
when the water pressure exceeds this level, the spring pressure is overcome and the valve is forced slightly open allowing excess pressure (and water) to escape
the valve can also be opened manually by flipping up the lever on the top, but this is not recommended on inspections
BTU rating of valve should be at least equal to boiler BTU rating

Generated explanation

Two simplified cross-sections show a boiler pressure relief valve in its closed and open states. On the left, spring force holds the poppet valve seated when water pressure is below the valve rating. On the right, pressure above the rating lifts the poppet, allowing water to discharge through the side outlet to a drain. A top-mounted manual relief lever can also lift the valve stem, with a dashed outline indicating lever movement. Notes identify 30 psi as a typical boiler relief pressure, require valve BTU capacity at least equal to boiler BTU rating, and discourage manual operation during inspections.

Components

pressure relief valve valve body spring valve stem poppet valve valve seat manual relief lever discharge outlet

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