Better hydraulic systems service

PS: The Preventive Maintenance Monthly, Dec, 2004

Mechanics, hydraulic system contamination causes aircraft problems and can cause crashes. Servicing aircraft reservoirs has been a problem.

Take the Apache, for example. The old way of servicing its reservoirs required:

* open cans of hydraulic fluid

* the use of potentially dirty tubes (which can cause contamination)

* sucking air into the reservoir.

But now the Army has a new standard 2-gal reservoir servicing unit (RSU). It provides quick disconnects and an easy and quick way to refill aircraft reservoirs with clean, moisture- and air-free hydraulic fluid. The RSU is a another tool to make servicing a little easier.

Initial issue to units will be configured with quick disconnect fittings based on the helicopter models in the unit.

For the AGPUs, you'll get a quick disconnect coupling used to fill AGPU reservoirs.

The basic RSU, NSN 4940-01-504-5279, is stocked without quick disconnects, but they are listed separately in the commercial manual as stocked items. NSNs are also available on the following: output hose, NSN 4720-00-484-5765, clear return tubing, NSN 4720-01-038-2651; and hose fitting, NSN 4730-00-472-4093.

WHEN YOU OPERATE THE RSU FOR THE FIRST TIME, HERE ARE SOME POINTS TO REMEMBER.

* The steps on flushing the hose, filling the reservoir, and stowing the output quick disconnects are listed on the reservoir's decal.

* Fluid is dispensed from the RSU using a manual pump, with a 200 psi output pressure.

* The output hose is fitted with a 2-micron filter to control solid contamination.

* A bulkhead connector and a return tube are provided to allow the output hose to be flushed prior to connecting to a bird.

* The return tube is transparent so that hydraulic fluid can be checked for air bubbles.

* The aircraft reservoir is filled by pumping the fluid through the quick disconnect fitting on the ground support return port for the hydraulic system to be serviced.

* The RSU delivers 4 cubic inches of fluid per stroke or a quart per 17 strokes.

The only maintenance requirement for AVUM is to replace the filter element in the output hose. But always make sure the RSU uses MIL-PRF-83282 as it says on the factory-applied label, since this fluid is used in all helicopter flight control systems.

Keep in mind that brakes use a different type of fluid, MIL-PRF-5606. For now, stay with the filter and bleeder assembly, NSN 4910-00-245-1832, to service brake systems.