A gradual increase in fill time is the classic sign of a wearing pump. Measure it so you can trend it: run a pump-up test and record the time (the Pump-Up calculator accepts seconds or minutes) — compare against previous tests or nameplate CFM.
1
Wear on valves, rings and gaskets
medReciprocating
CheckPump-up result 60–85% of nameplate and falling over time.
FixPlan a valve-plate and gasket service; schedule ring rebuild if blow-by present.
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2
Tank partly full of water
highCheckDrain tank fully — large volume of water/rust means effective tank volume is smaller (fills faster but empties faster too) and rust weakens the tank.
FixDrain daily or fit an auto drain. Have a heavily rusted tank inspected; replace if pitted.
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3
Hidden downstream demand
lowCheckClose the service valve and re-time. If time returns to normal, the extra time is demand/leaks.
FixLeak audit and repair.
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4
Overheating reduces output
medCheckUnit in a hot, enclosed space; head temperature very high. Hot intake air is less dense — about 1% less output for every 5°F rise.
FixImprove ventilation, duct intake from outside, keep cooling fins clean.
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Safety
Lockout/tagout before opening enclosures. Verify zero energy. Bleed system pressure before opening any pneumatic connection.