Modulating inlet or on/off unloader valve fails to respond to control air signal.
1
Diaphragm ruptured
Rotary screw
CheckRemove valve top cover (LOTO, 0 PSI verified) and inspect diaphragm for cracks/tears.
FixReplace diaphragm/seal kit.
SafetyLOTO and confirm 0 PSI before opening any pressurized valve body.
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2
Butterfly plate or shaft corroded/seized
Rotary screw
CheckAttempt to move plate by hand with valve depressurized.
FixFree up, lubricate per OEM, or replace valve assembly.
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3
Control air supply to valve blocked or leaking
Rotary screw
CheckVerify pilot air pressure at valve actuator matches OEM spec.
FixRepair pilot line, filter, or regulator.
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4
Return spring broken or fatigued
Rotary screwReciprocating
CheckVisual inspection after disassembly.
FixReplace spring/kit.
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5
Oil/varnish buildup gumming valve action
Rotary screw
CheckInspect for sticky residue on moving parts.
FixClean with OEM-approved solvent; investigate cause of carryover/varnish (oil degradation).
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Safety
Lockout/tagout before opening enclosures. Verify zero energy. Bleed system pressure before opening any pneumatic connection.