Skydrol 500B-4

Skydrol 500B-4 is a fire resistant phosphate ester hydraulic fluid for aircraft hydraulic systems. The first version of the Skydrol 500 series, Skydrol 500, was introduced in 1952, and steady improvements to the formulation led in 1977 to the current Skydrol 500B-4. It contains the same anti-erosion additive and acid scavenger found in Skydrol LD-4. It has low skin irritation and a low tendency to form mists that can irritate the respiratory tract, which has made it widely used in workshops and indoor test stands.

Typical Properties

• Clear, oily, purple liquid; specific gravity (25 °C) 1.050–1.062
• Viscosity 3.68–4.00 cSt at 99 °C, 11.40–12.40 cSt at 38 °C, max 2900 cSt at −54 °C
• Pour point max −62 °C; flash point (COC) min 177 °C; fire point min 191 °C; autoignition min 460 °C
• Acid number max 0.10 mg KOH/g; moisture max 0.20%
• Particle contamination (NAS 1638, AS4059F): 5–15 µm max 32,000; 15–25 µm max 5700; over 100 µm max 32