Don’t Pressure Load Your Pump Shaft!

Gear Pump

Ultimately, all pumps will fail. Even so, adherence to proper circuit conditions prolongs pump life. Bearings and shaft seals are common failure points that can be mitigated by properly selection and designing a hydraulic drivetrain. With design in mind, two factors that have a significant impact on bearing life are:

  1. Rotational Speed
    Bearing life is inversely proportional to pump shaft RPM. With this in mind, you should design your system accordingly. Simply put, by halving shaft speed, pump life is doubled.
  2. Pressure
    Pump life is also inversely proportional to the side load exerted on the pump shaft. This is a result of the pressure created at the pump outlet.

By taking these two factors into mind, you should design conservatively to increase drivetrain longevity. Follow the assembly checklist below to properly design and construct hydraulic drivetrains and proactively prevent mechanical damage, lubrication loss and catastrophic failure.

  • Remember oil cleanliness. Reducing contaminants within oil significantly reduces the risks of premature seal failure and bearing abrasion.
  • Ensure proper pump-motor shaft alignment by checking runout with a dial indicator. Misalignment will result in premature shaft seal failure. Coupling halves should have a gap of at least 1/16″, which prevents end loading of the pump shaft.
  • Remove heat proactively to reduce seal degradation and physical wear. This can be achieved by controlling viscosity and anti-wear additive breakdown within hydraulic fluid.
  • Always set system reliefs to their lowest pressure while fulfilling system operational requirements.
  • Use air bleeds. Inlet cavitation is a pump killer.
  • High case pressure results in excessive load on the shaft seal lip. This causes the seal lip to wear a groove in the shaft, eventually resulting in leakage. If case pressure exceeds the shaft seal’s design limits, instantaneous failure can occur.
  • Do not over-torque pump fittings and bolts. This can distort critical mating surfaces, resulting in wear anomalies.
  • Never force or pound a half-coupling onto the pump shaft, as damage to the retaining ring is likely to occur.

To learn more, contact your local Kaman Fluid Power to speak with a hydraulic specialist today.

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Frank Muisenga

Frank Muisenga

Project Manager at Kaman Fluid Power
As Fluid Power Project Manager, Frank designs hydraulic power units, electrical control panels and pneumatic systems based on customer specifications. He determines the proper components for the system and creates schematics. He also liaises with technical sales staff to meet with customers and assist in installation and troubleshooting.
Frank Muisenga

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