Shop Talk: Change in Hydraulic Fluid

Saturday, September 30, 2017

When Onboard Systems first developed the hydraulic release system for the TALON LC Hydraulic Cargo Hook, we used MIL-PRF-5606 hydraulic fluid (also referred to as MIL-H-5606), and that’s the hydraulic fluid we have supplied with every hydraulic cargo hook kit—until now.

Historically, commercial aircraft original equipment manufacturers (OEMs) and the military used petroleum-based hydraulic fluids (such as MIL-H-5606) that were not fire resistant. The US Navy took the lead in developing a fire-resistant hydraulic fluid, eventually issuing MIL-H-83282, which is a synthetic, hydrocarbon-based hydraulic fluid that can be used as a drop-in replacement for MIL-H-5606. MIL-H-83282 is rated to -40°F(4.4°C), due to high viscosity at low temperatures.

Due to the poor performance of MIL-H-83282 at low temperatures, MIL-PRF-87257 was developed. MIL-PRF-87257 has been validated for operation to -65°F (-53.9°C) and is also suitable as a drop-in replacement for both MIL-PRF-5606 and MIL-H-83282.

Since OEMs are requiring the more modern MIL-PRF-87257 fluid, Onboard Systems has decided to switch over to this standard, in both our our end user kits and in our test stands at our factory. This hydraulic fluid is backwards compatible with all Onboard TALON^® LC Hydraulic Cargo Hook kits, and is also interchangeable and miscible with MIL-PRF-5606 fluid, so you don't have to drain your established systems to start using the MIL-PRF-87257.

In a simple hydraulic system such as Onboard's cargo hooks, you can expect the same performance from the MIL-PRF-87257 fluid as with the original MIL-PRF-5606 fluid.

To support this change, we are switching the bleed kit that we supply with each new cargo hook kit to P/N 212-014-02, which uses the MIL-PRF-87257 fluid. Formerly bleed kit P/N 212-014-01 was supplied, which included MIL-PRF-5606 fluid.

Please contact us if you have any questions.

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