Skydrol LD-4

Skydrol LD-4 is a fire resistant, low density Type IV phosphate ester aviation hydraulic fluid introduced in 1977. It was developed to solve the problems of valve erosion and thermal stability common in earlier fluids. It combines low density, excellent thermal stability, valve erosion prevention and deposit control.

Typical Properties

• Clear, oily, purple liquid; specific gravity (25 °C) 1.003–1.013
• Viscosity 3.66–4.00 cSt at 99 °C, 10.65–11.65 cSt at 38 °C, max 2000 cSt at −54 °C
• Pour point max −62 °C; flash point (COC) min 160 °C; fire point min 177 °C; autoignition min 400 °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