Electric Hydraulic Power Unit Troubleshooting

As with any mechanical device, a hydraulic power unit will inevitably have many small problems in the course of its working life. You will not always have to call in someone to repair it, however. You can solve many of these sorts of problems on your own using some basic troubleshooting methods.

Hydraulic power units can have a host of different problems.

General Information

Keep in mind at all times how a hydraulics system is supposed to optimally work. Hydraulic systems create a flow of liquid, the resistance to which generates pressure. The flow of the liquid determines the actuator speed, while the pressure determines the actuator force. Fluid under pressure always takes the path of least resistance, and when fluid moves from a high-pressure area to a low-pressure area, and no work is performed in between, heat is generated.

Problems with a hydraulic system will fall into five major categories: excessive noise, excessive heat, incorrect flow, incorrect pressure and faulty operation.

Excessive Noise

Excessive noise can happen in three different sections of the hydraulic system: the pump, the motor and the relief valve.

Minor problems with noise might involve cavitation, or the creation of air bubbles in the pump's fluid. See whether any of the following solves this: replacing dirty filters, washing strainers in a solvent compatible with the system fluid, cleaning clogged inlet lines, cleaning or replacing the reservoir breather vent, changing the system fluid, changing to proper pump drive motor speed, overhauling or replacing the supercharge pump or checking whether the fluid is too cold.

More severe problems might be air in the fluid of your pump or a worn or damaged motor coupling. Try these tactics to fix these problems: tightening leaking connections, filling the reservoir to the proper level, bleeding air from the system or replacing the pump shaft seal.

The pump or motor coupling could be misaligned. Align the unit and check the seals, the bearings and the couplings.

The relief valve could be improperly set, requiring the pressure to be reset using a pressure gauge.

Finally, a worn or damaged pump or worn poppet or seat on the relief valve requires an overhaul or replacement of the part.

Excessive Heat

Excessive heat can occur in the pump, the motor, the relief valve or the fluid.

Once again, first check for minor problems using the measures mentioned in the above section. Check the valve setting.

More extreme problems with heat include an excessive load on your motor. Check the condition of your motor and see whether it is being pushed to hard. Your pump, your motor or your relief valve could also be worn or damaged, which means one or all of these devices require replacement.

In the case of heated fluid, first check to see whether the fluid is set too high. Then check to see whether the fluid is dirty or almost running out. Check the fluid viscosity. Check the fluid cooling system for malfunction, and clean the cooler and/or the cooler strainer if it needs it. If this doesn't help, replace the cooler control valve, and if none of that works, repair or replace the cooler. However, a worn or damaged pump, motor, valve or other component in the system could be to blame as well.

Incorrect Flow

If you are getting no flow in your hydraulic motor, check to see whether the pump is receiving fluid. Check to see that the pump is operating properly and repair or replace it. Check for shearing on the pump-to-drive coupling. Check to make sure the pump motor is rotating in the proper direction. Check to see whether the directional control is set in the wrong direction. Check to see whether the entire flow is passing over the relief valve. Finally, check to see whether the pump is damaged.

Low flow can be caused by simply having the flow set too low, the relief or loading valve set too low, the flow could be bypassing through an incorrectly opened valve, an external leak in the system, an inoperative yoke-activating device, an incorrectly calibrated pump motor, and finally, a worn-down pump, motor or other component.

Incorrect Pressure

No pressure in your hydraulic system means no flow, so go back to the incorrect flow system.

Low pressure can be caused by a pressure-reducing valve being set too low, the valve being damaged or a damaged pump, motor or cylinder.

Erratic pressure can be caused by air in the fluid, a worn relief valve, a contaminate in the fluid, a defective accumulator or a worn pump, motor or cylinder.

Excessive pressure can be caused by a misadjusted or damaged relief, reducing, or unloading valve, or an inoperative yoke actuating device.

Faulty Operation

An inert hydraulic machine can mean that a bind has occured somewhere in the machinery, that there is no command signal to the servo amplifier, the servo valve is inoperative or misadjusted, the servo valve is inoperative or the motor and/or cylinder are worn or damaged. Check all these problems and take the necessary steps to fix them.

Slow movement can be a result of low flow, an excessively high fluid viscosity, valves with insufficient control pressure, no lubrication for the machine ways or linkages, a problem with the servo aimplifier and valve or a worn or damaged cylinder or motor. Check for each of these problems in turn.

Erratic movement can be caused by erratic pressure (see section on incorrect pressure), air in the fluid, no lubrication, an erratic command signal, servo amplifier problems, a malfunctioning feedback transducer, a sticking servo valve or a worn or damaged cylinder or motor.

Excessive movement can be caused by excessive flow (see incorrect flow section), a feedback transducer malfunction, a misadjusted or malfunctioning servo amplifier or an excessive workload on the machine.