Hydraulic, Pneumatic, and Fuel Systems
Hydraulic, Pneumatic, and Fuel Systems tests fluid power, bleed-air services and fuel management. Expect pressure, flow, force and quantity calculations plus system safety logic.
Hydraulics
Pascal's law: pressure is transmitted undiminished. Actuator force = p × A. Pumps supply flow, not pressure; pressure is set by load and relief valve. Accumulators store energy and damp pulses; check valves set direction; filters protect servo valves. Skydrol is phosphate-ester, hygroscopic and attacks some paints and seals.
Pneumatics and fuel
Bleed air supplies air conditioning, pressurisation, anti-ice and engine start; leak detection loops close the bleed valve. Fuel systems use boost pumps, crossfeed, vent and jettison. Mass = volume × specific gravity; water settles because it is denser than fuel, and microbial growth occurs at the fuel-water interface.
Worked example
A hydraulic pump delivers 20 L/min at 210 bar. Flow = 20/60,000 = 3.33 × 10^-4 m³/s. Hydraulic power = Q × Δp = 3.33 × 10^-4 × 21,000,000 = 7,000 W = 7 kW. If an actuator has 10 cm² area, force at 210 bar is 21,000,000 × 0.001 = 21,000 N (21 kN).
Traps
Using bar as 10^5 Pa is correct, but 1 bar = 100 kPa, not 1 MPa. Gauge pressure excludes atmosphere; absolute pressure includes it. Do not add fuel volume without temperature and specific-gravity correction. A pneumatic leak can be invisible and hot.