TL;DR
Slow actuator movement with low system pressure usually means the pump is worn and bypassing internally. Measure case drain flow: if it is more than 10% of rated pump displacement, the pump is at end of life.
What you might see
- actuator cycle time longer than normal
- system pressure does not reach setpoint under load
- pump flow below rated GPM or L/min
- motor current lower than normal at same load
Likely causes
Worn piston slippers, barrel, or valve plate causing internal bypass in the PV piston pump
Reduced pump speed from a worn or slipping coupling between motor and pump
System pressure relief valve set too low or stuck partially open, limiting effective system pressure
Contaminated fluid accelerating pump wear beyond the normal service interval
Required tools
- LOTO kit
- Inline hydraulic flowmeter
- Pressure gauge calibrated to system pressure range
- Graduated container and stopwatch (for case drain test)
- Hydraulic fluid sample kit
Safety first
- Hydraulic systems store lethal energy in pressurized fluid and accumulators. Always depressurize and verify zero pressure before breaking any connection.
- Hot hydraulic fluid causes serious burns. Allow the system to cool before opening any fittings if fluid temperature exceeds 50 degrees C.
Procedure
- 1
Lock out the prime mover and relieve all hydraulic pressure before any inspection.
Warning: Hydraulic systems store energy. Verify zero pressure on the accumulator and all cylinders before breaking any fitting. - 2
Review the hydraulic fluid sample results if available. Contamination above ISO 4406 class 18/16/13 accelerates pump wear significantly.[1]
- 3
Reconnect and run the system. Measure pump outlet flow at rated pressure using an inline flowmeter. Compare to the rated displacement on the Parker PV pump nameplate.
- 4
Measure case drain flow at the drain port with a graduated container and stopwatch. Case drain above 10% of rated displacement indicates significant internal wear.[1]
- 5
Check the coupling between the prime mover and pump for wear, cracked spiders, or looseness.
- 6
Verify the main relief valve setting with a pressure gauge. Adjust to the system design pressure if it has drifted low.
- 7
If case drain exceeds 10% or flow is more than 15% below rated, plan a pump replacement. Continue operating only if the application allows reduced performance and safety margins are maintained.
- 8
When replacing the pump, flush the system and replace the hydraulic filter before first start on the new pump.
Sources
Parker PV Series Variable Volume Piston Pump Service Manual, Parker Hannifin Corporation
Parker PV Series Piston Pump Service Manual, pump performance testing and case drain flow specification (general)
View source
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