11.11 - Hydraulic Power Flashcards
What systems use hydraulic power?
- Landing Gear system
- Flight Control System
- Opening and closing freight compartment doors
What should be the only component fitted between the Reservoir and the pump?
Only component that can be fitted between reservoir and pump (supply line) is a:
Fire Shutoff valve
List the components in order from the reservoir to the system and back?
Supply line, Fire Shutoff valve, motor driven pump, pressure switches, pressure relief valves, filter, check valves, hydraulic manifold, accumulator, return line and return filter
List the properties of a good hydraulic fluid?
- As incompressible as practical
- Low viscosity to minimise friction during flow
- Chemically stable
- Good lubricating properties
- Not foam in operation
- Compatible with materials that seals are made with
- high flash point (temp to ignite)
- high fire point
List the 2 types of hydraulic fluid?
Mineral base & Synthetic base
Why is the reservoir pressurised?
(Internal pressure of reservoir?)
The hydraulic fluid in the reservoir is pressurised to supply the pump with fluid correctly. (To prevent pump cavitation)
(30 psi internal pressure of reservoir)
What are the typical pressures for pressuring a hydraulic system and reservoir?
Pressurising the hydraulic fluid can be done in two ways,
By air pressure or by hydraulic pressure
3000 psi system pressure
30 psi internal reservoir pressure
Explain the purpose of a wobble plate in a variable speed variable displacement pump?
The position of the wobble plate moves every piston in and out of the drilled hole once during one revolution.
This is called the ‘‘stroke’’ of the piston and it’s length cab be changed according to pressure.
What methods are used to drive hydraulic pumps?
The main pump which drives main systems is normally installed on the engine and is driven by it.
Auxillary subsystems are used on ground when engines not running and for backup during flight operation. These pumps may be driven by:
Electrical motor, Pneumatic turbine, RAT (Ram Air Turbine), hand and hydraulic motor (PTU)
Explain the purpose of a P.T.U?
A P.T.U (Power Transfer Unit) may be used to transfer hydraulic power from one sysem (Green system) to drive a separate motor of another system (yellow system) or vice versa (Yellow to Green)
NOTE: There is no transfer of fluid from one system to another. Only transfer of power to power motor
How do you check to see if a filter has been bypassed?
When filter becomes dirty, filter lets through less liquid which decreases power/ system pressure.
A magnet holds an indication knob in the filter housing and once a pre-determined value is reached, a small spring pushes the indication knob up indicating the filter needs changing.
Explain the difference between a check valve and an orifice flow check valve (restrictor valve)?
A check valve allows fluid to flow in one direction only. (Spring tension)
An Orifice flow check valve (restrictor valve) allows fluid to flow in one direction only and restricted flow in another direction
Describe the functions of an accummulator?
List the parameters that have to be monitored in a hydraulic system? (5)
- Quantity of hydraulic fluid in the reservoir
- Pressure of the hydraulic fluid in the system
- Output pressure of pumps
- temperature of hydraulic fluid
- internal pressure of reservoir
What is the most common hydraulic fluid used in transport aircraft? (2)
Two basic types of hydraulic fluids are used in transport aircraft hydraulic systems:
- Mineral base
- Synthetic base
For the operation of which system can a hydraulic system be used?
- Landing gear system
- Flight Control system
(Opening and closing freight cargo doors on some aircraft)
Why are the hydraulic tanks pressurised?
How is it done? (2 ways)
The hydraulic fluid in the reservoir is pressurised to supply the pump with fluid correctly. (stop pump cavitation)
Pressurising the hydraulic fluid can be done in two ways, by air pressure or by hydraulic pressure.
What is the purpose of the auxillary hydraulic system?
The auxiliary system can be used if something should happen to one or both engine driven pumps in flight.
When does a check valve open?
A check valve opens when there is sufficient pressure (15-25 PSI) to overcome the spring tension allowing flow in one direction.
A check valve opens easily, but also closes quickly as soon as the pressure to the valve decreases.
Describe the functions of an accumulator?
To achieve a good supply to the pumps, what 2 requirements must be met in the supply line?
- Don’t install components in supply line except fire shutoff valve
- Use a supply line with a relatively large diameter (and short a distance as possible)
Explain Case Drain fluid
Case drain system is hydraulic fluid used for cooling and lubrication purposes before being redirected back to reservoir
