Hydraulic Power Unit Troubleshooting


Pumps in hydraulic power units (HPUs) serve numerous roles. A controlled crown rolls HPU. For having a functioning Hydraulic Power Unit, we would require the following pumps.

  • High-pressure pumps that use hydrodynamic or hydrostatic load shoe bearings to manage shell deflection.
  • Lubrication pumps for lubricating shell load shoes, rotating bearings, and temperature control
  • Oil scavenger pumps are used to restore oil to the hydraulic unit.

Pump failures will result in product quality issues and a loss of production. There will usually be one or more backup pumps to reduce the chance of a pump failure influencing production. Thus, in this article, troubleshooting these pumps and their causes will be looked into.

Pump Cavitation

The failure of a gas hydraulic power pack pump to pull in a complete charge of oil is referred to as cavitation. When a pump begins to cavitate, the noise level rises, and the area surrounding the shaft and front bearing may get quite heated. Other signs of pump cavitation include:

  • Inconsistent cylinder movement.
  • Difficulties building up to full pressure.
  • A milky look of the oil.

If cavitation is detected, inspect the following areas:

  • Examine the condition of the pump suction strainer. Even if it does not appear to be unclean, clean it. After using a solvent, the blast dries using an air hose. Varnish deposited in the wire mesh may limit oil flow but is nearly unnoticeable. If you notice varnish deposits on the inside surfaces of pumps or valves, the system is overheating. It is necessary to install a heat exchanger.
  • Examine the pump input piping for any restrictions or clogs. If hoses are used, be certain that they are not collapsed. Only vacuum-rated hoses should be used in the pump’s input. They contain an interior wire helix to keep them from collapsing.
  • Check that the air breather on the reservoir’s top is not blocked with lint or debris. If the breather became blocked in systems where the air volume above the oil is relatively modest, the pump might cavitate during its extension stroke.
  • The oil viscosity may be “too high for the specific pump.” Some pumps cannot take up the prime on heavy oil and must operate in a somewhat cavitated state.

Air Leaking Into the System

After a short period, the air in a newly built system will purify itself. The system should be cycled for 15 to 30 minutes before creating more than very low pressure. Entrapped air will dissolve slowly in the oil and be transferred into the reservoir, where it will escape. Of course, leaking air from high places in the piping, particularly around cylinder ports, can speed up the process.

Air entering the system through air leaks will cause the oil to appear milky for a brief period after starting, but the oil will normally clear up around an hour after shutdown. Examine the following places to determine where the air is entering the system:

  • Ensure that the oil reserve is full and that the pump intake is considerably below the minimum oil level. According to the NFPA reservoir regulations, the highest point on the suction strainer must be at least 3 inches below the minimum oil level.
  • When all cylinders are extended, check the oil level to ensure it is not below the “Low” indication on the gauge. However, do not overfill the reservoir; it may overflow when the cylinders are retracted.
  • The air might be getting in near the pump shaft seal. A little vacuum will exist behind the shaft seal of gear and vane pumps sucking suction oil from a reservoir positioned below them. When this seal wears out, air can enter through the worn seal. Behind the shaft seal, piston pumps typically have a little positive pressure of up to 15 PSI.

Water Leaking Into the System

Water flowing into the system causes the oil to appear milky while the system is running, but the oil normally clears up quickly once the system is turned off as water settles to the bottom of the reservoir. The water may enter the system in the following, and potentially more, ways:

  • A shell and tube heat exchanger leak might enable water to mingle with the oil.
  • Condensation on the reservoir’s interior walls. This is virtually inescapable for systems that operate in environments where the ambient temperature fluctuates from day to night.
  • The right approach is to regularly remove a tiny amount of fluid from the reservoir’s bottom. Because water sinks to the bottom, it will drain before the oil emerges.
Oil Leakage Around the Pump

Water Leakage Around the Shaft Some pumps (hydraulic pumps or those with an overhead reservoir) may have a tiny pressure behind the shaft seal. This is generally more noticeable when the pump is operating and may fade when the pump is turned off. Exterior leakage may occur as the seal wears out.

Other pumps, such as gear and vane, typically operate with a little vacuum behind the seal. Leakage may occur only after the pumps have been turned off. Excess oil temperature might cause prematurely worn shaft seals. Rubber seals have a relatively short life at temperatures above 200°F. Abrasive particles in the oil can quickly wear down seals and cause circumferential scoring of the shaft in the seal region. If abrasives are found, they will precipitate out of a reservoirs sampling.

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