Systems 3 Hydraulics
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State Pascals Law
Pressure applied is distributed equally to all areas of a non compressible fluid.
Strictly speaking only true if nothing moves
Pressure force equation
Force = Pressure x Area
Work = MAD
Work = Force x Distance
what is a key quality of hydraulic fluid
Incompressible through it's entire range of approved operating pressures.
Any work done compressing the fluid is wasted
Mineral or Petroleum based fluids show what characteristics
- Red in Colour
- Smell like penetrating Oil
- Used with Synthetic rubber, leather, or metal seals
- Disadvantage is flammability!
- Corrosive to natural rubber
- DTD 585 UK
- MIL-H-5606 USA
Vegetable based Fluid
- Caster Oil & Alcohol
- Older types of A/C
- Smells like alcohol
- Coloured Blue
- Used with Natural rubber seals
- Disadvantage is flamability
- Used in high performance A/C
- High Temp Range -55 +105
- SkyDrol 500B and LD
- Purple in Colour
- fire resistant
- seals are Silicon, flourocarbon, or butyl
- Attacks PVC and wire insulation
- systems must be sealed due to water and atmospheric contaminants
What is the name of the pipe that stands proud in the Reservoir so fluid will stop feeding the power pump in the event of a leak but still leave fluid for the hand pump
What pressure are pressurized systems?
Why are they pressurized?
How are they pressurized?
typically 10psi, up to 30psi in high demand high alt situations
stops cavitation and in low pressure environments
From bleed air from engine compressor
Spur Gear pumps are for what volume and pressures
Medium fluid volume
up to approx 1500psi
Name the 2 types of constant displacement pumps
Variable displacement pumps are used for what type of system
What does this system need?
Constant Pressure, live line systems
Bypass valve to prevent over-pressurizing if pump fails to stop delivering when it should
What is the common type of variable displacement pump?
Axial swash plate pump.
What is a variable pump said to be doing when it is delivering no fluid
State if idling
When will a hand pump be used?
- in emergency situations
- to allow ground servicing without engine runup, such as
- pressure joints and lines can be tested
- cargo doors etc opened
Pump is normally double acting
Purpose of Cut out valve
In a constant pressure system, to return fluid to the reservoir when the required line pressure is achieved
what does a short interval of a cut out valve indicate?
A possible leak in the system
Or if the accumulator gas pressure is too high it wont store much fluid and so it is exhausted quickly and cuts in the valve again.
What does a "too low" gas pressure in an accumulator cause?
No longer serves its function of "dampening" the system, so gets a knocking noise "Hammering"
Purpose of a thermal relief valve
To relive high pressure caused by thermal expansion in a trapped part of the system (between a non-return valve and a piston for example)
Operates at higher pressures than normal pressure relief valves in the system
where is the shut off valve in the system
Between Reservoir and pump
for ground servicing, and to isolate in the event of an engine fire.
Purpose and uses of Hydraulic Fuse
To stop fluid loss downstream when a leak occurs. Operate when pressure drop across the fuse exceeds a limit.
- Thrust reverse
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