Output from a PumpMD presents historical data of an axial-piston hydraulic pump operating five days over a four-month period.After placing the pump into service, the piston shoes will wear over time. Wear occurs in proportion to the cleanliness of the oil being pumped—the dirtier the oil, the more rapid the wear. This wear increases oil flow to the pump case, pump-case temperatures, and case pressure from the backpressure that develops behind the case drain port. The increased pump-case pressure can affect the hydrostatic balance of the pistons, causing leakage through the pump-shaft seal.
When one or more internal components of a pump fails, metallic debris becomes scattered throughout the pump cavity and eventually works its way out into the rest of the hydraulic system, putting all other components at risk of premature failure. The result is usually much more than the expense of repairing the pump.
Because the debris will likely circulate through the entire hydraulic system, extensive assessments should be performed to ensure other areas have not become vulnerable. As wear degrades a pump’s critical tolerances, excess fluid leaks past internal seals and moving parts into the case, robbing the pump of efficiency. Moreover, the associated downtime often results in thousands of dollars in lost production.
Pump Diagnosis Through the Case Drain
When taking all of this into account, it becomes evident that the case drain can be a key indicator of a pump’s health by monitoring flow, temperature, and pressure. Furthermore, this all can be done while the pump is running. Case-drain flow exceeding a percentage of total pump output signals the need for maintenance or complete pump rebuild.
Many manufacturers offer axial-piston hydraulic pumps with similar power, pressure, and flow ratings. But rarely do any two pumps share the same dimensional and performance characteristics. This makes it difficult to establish baseline performance criteria for any given pump model.
