The small unloader valve on the side of the pressure switch should be closed while the motor runs, open for a moment when it stops (to dump the discharge line so the motor can restart unloaded), then close. Leaking while running wastes air; never bleeding causes hard starts and tripped breakers.
1
Unloader valve O-ring/pin worn — leaks while running
lowReciprocating
CheckWith the pump running, soap-test the unloader. Bubbles = leak. Tank fills slower than normal.
FixReplace the unloader valve (often sold separately) or the whole pressure switch if integral.
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2
Unloader lever bent or out of adjustment — never opens
medReciprocating
CheckStop the motor at cut-out: you hear no bleed puff. Then attempt restart with tank full: motor hums, struggles, or trips breaker.
FixAdjust or replace the unloader actuator; replace switch if the lever is part of the switch.
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3
Bleeds constantly after stop — check valve leaking back
medReciprocating
CheckIf the bleed never stops after shutdown, the tank is emptying back through the line. See 'Tank check valve leaking back'.
FixClean/replace the tank check valve.
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Safety
Lockout/tagout before opening enclosures. Verify zero energy. Bleed system pressure before opening any pneumatic connection.