The ASME safety valve on the tank opens when tank pressure exceeds its stamped setting. It's doing its job — the real problem is upstream: the compressor isn't stopping, or the valve itself is weak.
1
Pressure switch not cutting out
criticalCheckWatch the gauge as the valve pops — pressure at or above the valve setting means the switch didn't stop the motor.
FixSee 'Pressure switch won't shut compressor off'.
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2
Safety valve weak / set too low
medCheckValve opens below its stamped pressure (verify with a test gauge).
FixReplace with the same or correct set pressure for the tank; do not reset or tamper.
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3
Gauge reading low (hidden over-pressure)
medCheckCompare tank gauge to calibrated test gauge.
FixReplace gauge; re-set the switch.
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Safety
Lockout/tagout before opening enclosures. Verify zero energy. Bleed system pressure before opening any pneumatic connection.