Aircraft Hydraulic Fittings Catalog by AN, MS and NAS

Hydraulic fittings work by applying a force at one point which is transmitted to another point using an incompressible fluid. In aircraft, this fluid is usually an oil. Landing gear, flaps, and brakes all work using a hydraulic system. High pressure is transmitted through the fluid connected to separate components, therefore the fittings used to construct the hydraulic system must be sturdy and able to withstand high pressures.

O-rings are a specific type of seal that are often used in aircraft hydraulic systems. Valves are paired with o-rings within hydraulic systems due to the additional pressure involved in the hydraulic process. O-rings are more preferable than metal-to-metal fittings because they do not add strain to the thread of a hardware piece. Distortion can occur when a metal fitting has been fastened too tightly. As a result, metal fittings can crack under the additional strain. Unlike metal hardware, o-rings do not tighten over time, therefore do not require the same amount of routine maintenance. A disadvantage of o-rings is that there are not reusable, nor are they interchangeable. Despite having no obvious signs of wear and tear, o-rings must be replaced to avoid any leakages.

Two types of valves that feature in hydraulic systems include, relief valves, and selector valves. In the case of built up fluid pressure, a relief valve can be opened to alleviate the pressure. Selector valves are used to control directional flow.

Hydraulic o-rings were established by the US Air Force-Navy (AN) specification numbers, 6227, 6230, and 6390 for use in fluid at operating temperatures ranging from -65 °F to over 160 °F. Since then, newer compounds have been developed using military standard. The MS standard for o-rings operating in a temperature range of -65 °F to 275 °F are the MS28775 and the MS28778. The rings are made from nitrile butadiene rubber, which is resistant to petroleum-based hydraulic fluid.

We at, ASAP NSN Hub, owned and operated by ASAP Semiconductor, supply hydraulic fittings worldwide. We supply hydraulic fittings that are manufactured to AN, NAS, and MS standards. Use our optimized search engine to find the exact part you need.