The Weeping Relief Valve and the Weekend Heat Demand
A 40-unit apartment building is heated by a 1950s cast-iron sectional boiler whose nameplate reads 15 psig maximum working pressure, steam. On Friday afternoon the relief valve on the boiler top begins weeping steadily at about 8 psig on the boiler gauge. The building handyman, who holds a low-pressure boiler operator license, has a plan: remove the relief valve and plug the opening so the building has heat over the weekend, then on Monday have a contractor install a 30 psig relief valve from his truck because "the old one is too small and lifts all the time." The gauge glass shows a normal level, the pressuretrol is set to cut out at 12 psig with a 4 psi differential, and the burner is firing normally. The owner wants heat back before the cold snap, and there is no spare relief valve in the building.
1. Evaluate the handyman's plan. Is any part of it acceptable, and what is the correct outcome?
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No part of the plan is acceptable.
- Plugging the opening creates an unprotected pressure vessel. This is a low-pressure steam boiler limited to 15 psig; with the relief valve removed there is nothing to stop the burner from taking the boiler past its design pressure if the pressuretrol fails or the control circuit hangs up.
- Installing a 30 psig valve is equally unsafe. A relief valve set above the boiler's maximum allowable working pressure can never protect the boiler, because the boiler will be damaged before the valve reaches its set pressure. A relief valve is selected to open at or below the boiler MAWP and must have a relieving capacity at least equal to the boiler's rated capacity.
- The correct outcome is replacement with a valve of equal or greater capacity set at or below 15 psig, installed with no shutoff valve between the boiler and the valve, and with full-size discharge piping to a safe point of discharge.
If the correct valve is not on hand, the boiler stays cold and temporary heat is brought in. No heat is a comfort problem; an unprotected boiler is a life-safety and insurance problem, and it is also a licensing problem for the operator who allows it.
2. Before condemning the relief valve, what must be verified? The gauge reads only 8 psig when the valve lifts.
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A relief valve opens at its stamped set pressure, so either the valve is defective or the true pressure is higher than the gauge shows.
Verify in this order:
- Gauge accuracy - compare against a known test gauge at the same tapping, and confirm the siphon is not plugged and the gauge cock is fully open. A gauge with a plugged siphon or a partially closed cock can read low.
- Control settings and behaviour - with a 12 psig cut-out and a 4 psi differential, the boiler floats between roughly 8 and 12 psig. Watch the gauge through a full cycle to see where the burner actually shuts off.
- Valve condition - debris or scale on the seat, a corroded spring, or a valve that has been manually lifted and not reseated will cause premature lifting. Check the valve's stamping to confirm the set pressure and capacity are correct for this boiler.
- Discharge piping - confirm it is not blocked, reduced, or valved off, which can hold the valve off its seat.
A relief valve is not field-repaired or field-adjusted by the operator. If it lifts below its stamped pressure it is replaced, or sent to a qualified shop that resets it, restamps it, and seals it.
3. What should be recorded and communicated, and what is the operator's personal exposure here?
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The operator's license is personal and follows the individual, not the building.
- Log it: the date, time, observed pressure, gauge reading, valve stamping, actions taken, and the name of everyone involved. Note that the boiler was taken out of service and why.
- Notify the owner in writing - not verbally - that the boiler cannot be fired without a properly sized and set relief valve, and that plugging or oversizing the valve is prohibited. Written notice protects the operator and forces the owner to own the decision.
- Notify the enforcing authority and the insurance carrier as required, particularly if anyone plugs a safety device or if the boiler is returned to service without correction.
- Do not sign or initial anything describing the boiler as safe or ready while the valve is missing or wrong.
Allowing a relief valve to be plugged, or knowingly firing a boiler so protected, exposes the operator to suspension or revocation of the license, civil liability, and potential criminal liability if someone is injured. Refusing and documenting the refusal is the defensible position.