Hydraulic and Pneumatic Systems Flashcards

What color is MIL-PRF-5606 mineral-based hydraulic fluid?

Answer: Red

MIL-PRF-5606 petroleum-based fluid is dyed red for identification.

Which seal material is compatible with phosphate ester (Skydrol) hydraulic fluid?

Answer: Butyl rubber or ethylene propylene

Phosphate ester fluids attack nitrile and neoprene, so butyl or EPR seals are required.

What is the typical color of Skydrol phosphate ester hydraulic fluid?

Answer: Light purple

Skydrol fluids are dyed light purple to distinguish them from mineral-based fluids.

Before checking the air preload on a hydraulic accumulator, what must be done?

Answer: Relieve all hydraulic system pressure

Preload can only be read accurately when fluid pressure is zero so the gauge shows nitrogen charge alone.

A 1,000 psi hydraulic pressure acts on a piston with a 2-square-inch area. What force does the piston produce?

Answer: 2,000 pounds

Force equals pressure times area, so 1,000 psi x 2 sq in = 2,000 lb.

What is the function of a check valve in a hydraulic system?

Answer: Allow fluid flow in one direction only

A check valve permits free flow one way and blocks reverse flow.

In a system with a constant-delivery pump, what does the pressure regulator (unloading valve) do when system pressure reaches its set value?

Answer: Routes pump output back to the reservoir at low pressure

The regulator unloads the pump by sending its output to return at low pressure, so the pump is not working against full pressure.