Portable hydraulic test stands are manufactured in many sizes and cost ranges. Some have a limited range of operation, while others can be used to perform all the system tests that fixed shop test stands are designed to perform. For example, one particular type of portable test unit can perform the following functions:

1. Drain the aircraft hydraulic system.
2. Filter the aircraft system hydraulic fluid.
3. Refill the aircraft system with clean, micronically filtered hydraulic fluid.
4. Check performance of aircraft systems and subsystems.
5. Check the aircraft hydraulic systems for internal and external leakage.

This type of portable hydraulic test unit is usually an electrically powered unit. It uses a hydraulic system capable of delivering a variable volume of fluid from zero to approximately 24 gallons per minute at variable pressures up to 3,000 psig. The test unit and its components are mounted on a metal base enclosed by a removable top cover. The base is usually mounted on four pneumatic rubber tire wheels. It may be selfpropelled or provided with a tow bar for towing by hand or vehicle.