Hydraulic Power Units

Hydraulic Power Units

Hydraulic Power Units (HPUs) are a type of portable ground support equipment that provides pressurized hydraulic fluid for performing many types of aircraft maintenance. They are designed to assist in the operation and testing of the hydraulic systems in aircraft to ensure that the hydraulic components and systems are functioning properly.

They are typically used to check the aircraft hydraulic systems for operation and leaks, drain the aircraft hydraulic systems, filter the aircraft system hydraulic fluid and refill the aircraft system with clean fluid.

Hydraulic Power Units are used in most aircraft maintenance shops and for many types of commercial, business and general aviation aircraft. They are available in many different sizes and fluid capacities. Hydraulic Power Units are capable of delivering pressures over 3,000 psi and hydraulic fluid flow over 20 gallons per minute. A cooling system is installed in most units to allow for continuous operation.


Safe Use of Hydraulic Power Units

The equipment should be maintained in a safe and clean condition at all times during use. When operating the unit, the following safety precautions should always be followed.

  • Hydraulic Power Units must always be used in accordance with the equipment operator manuals in conjunction with the appropriate aircraft maintenance manual. These manuals contain specific safety information that needs to be followed for the operation of the equipment. The HPU must only be operated by personnel trained in the proper use of the specific unit.
  • Safety glasses should always be worn when operating the unit. The Material Safety Data Sheet for the appropriate fluid type should also be consulted for other personal protective equipment that may be required before operating the equipment.
  • The operator’s hands, feet, hair, and any loose clothing should be kept away from all moving parts to prevent injury.
  • The equipment’s power switch must be in the ‘OFF’ position when connecting or disconnecting hoses to the aircraft.
  • The unit should never be operated with the equipment’s covers, panels, or guards removed.
  • Before performing any type of service on the HPU, the electrical power supply should be disconnected to prevent the unit from starting accidentally. The bypass valve should also be opened to relieve any residual internal pressure within the system.


Hydraulic Power Unit Maintenance and Storage

It is important that regular preventive maintenance and calibrations are performed on all Hydraulic Power Units to ensure that the equipment is operating properly and accurately. This should be scheduled to be completed at least every year, with more frequent maintenance performed depending on how the unit is used. By performing regular maintenance, the equipment’s usable life will be extended and it will require less unscheduled maintenance, thus reducing overall operating expenses.

Some of the main maintenance and calibration tasks that need to be performed are:

The filters need to be replaced to maintain the cleanliness of the hydraulic fluid in the system. The scheduling of the filter changes depends on the frequency of use of the unit along with the environmental conditions to which the equipment is exposed. At a minimum, filters should be replaced annually.

It is important that the hydraulic fluid within the HPU is clean so that contaminants are not introduced into the aircraft hydraulic systems. The hydraulic fluid needs to be periodically monitored and a sample analyzed for contamination. The sample is usually either sent to an external laboratory or is analyzed on-site using a portable contamination device. The outcome of this process can be used to determine the proper frequency for filter changes.

All hoses, connections and power cords should be inspected for any damage, cuts, leaks, or loose fittings. At high pressures, a small pinhole leak from a damaged hose can act like a saw and cut through many objects, especially human skin. If the conditions cannot be repaired, the hoses or components should be replaced.

The gauges that monitor the system pressures must be calibrated to make sure that they are indicating within the manufacturer’s specifications. Gauge calibration should also be performed annually, at a minimum.

If the Hydraulic Power Unit will not be used for an extended period of time, the fluid reservoir should be completely drained. The unit should then be covered appropriately in order to be kept clean, dry, and free of contaminants. The equipment’s hoses should be stored by winding them on a reel so they can be kept free of kinks and twists.

can provide the appropriate maintenance and calibration services for a wide variety of Hydraulic Power Units. For more information on our GSE maintenance and calibration capabilities, contact e2b calibration.


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