Hydraulic principles Flashcards
How do you calculate the force produced by a pressure exerted.
Pressure of master cylinder x size of actuator. E.g. 300psi from master cylinder for a 10inchx10inch actuator = 300 x 100 = 300,000
What is the purpose of the reservoir?
Store a supply of fluid under pressure (from compressor bleed air)
What is the purpose of a check valve?
Only allows fluid to travel in one direction
What is the purpose of a selector valve?
allow fluid to operate in multiple directions, required for systems with 2 positions (e.g. gear up/down)
What is the purpose of the restrictor valve?
Restricts to flow of fluid to prevent cavitation
In regards to the gear, where is the restrictor valve usually located?
In the up line (used to slow gear down extension)
Describe a constant displacement pump
Fluid delivery is independent of system demand. The system will oversupply during periods of low demand. Therefore a pressure regulator is required.
Describe a variable displacement pump
Pump still runs at fixed RPM but the fluid output is altered to match supply demand. Pressure relief valve is used instead of pressure regulator
What is the purpose of the Pressure accumulator
Dampens fluid surges (hammering and knocking), and also provides emergency pressure. A gas is stored at half the pressure of the hydraulic fluid.
What is the purpose of the pressure regulator?
Maintains the pressure of the PUMP (as opposed to the whole system like a pressure relief valve)
What is the purpose of the pressure relief valve?
Maintain pressure for the SYSTEM (as opposed to the pressure regulator which regulates the pump only)
What is the purpose of the shuttle valve?
Allows alternate sources to provide hydraulic fluid/pressure
What is the purpose of a demand (scavenge) pump
Pumps within the hydraulic lines that help maintain pressure for individual components. Only activated when pressure requires help.
What type of hydraulic pumps are typically fitted to large jet transport aircraft?
Variable displacement gear type
How are backup/demand pumps driven?
Primarily by pneumatics, if the engines aren’t on (therefore no compressor air), they are electrically driven, and if everything fails, they are driven by a RAT.
