TOPIC 1: Hydraulic and Pneumatic Systems Flashcards
Pascal’s law states what?
This if there is an enclosed vessel full of liquid and you apply a force to a piston in the vessel to raise the pressure, this increase in pressure will be the same anywhere in the system
State the definition of force?
Is energy exerted or brought to bear and is the cause of motion or change (caused by hydraulic or pneumatic action or by a spring) (expressed in pounds, grams or kilograms)
State the definition of pressure?
Is when a force is applied over a given area (expressed in pounds per square inch, PSI or grams per square inch g/cm2 )
State the definition of work and how is it calculated?
- Any time a force causes an object to move (expressed in foot-pounds lb/f or in kilogram-metres kg/m)
- Work = force x distance
How is power calculated?
FORCEXDISTANCE/TIME
How is mechanical advantage defined?
The ratio of output force to the input force applied to a mechanism
What are the two major advantages hydraulic systems has over other types of mechanical systems?
- Ease with which force can be transmitted over large distances and into and out of sealed compartments
- The large gain in mechanical advantage made possible by varying the size of pistons
What functions does the reservoir conduct in regards to the hydraulic system?
- ensure a good supply of fluid to the pump
- cater for ram displacement
- allow for thermal expansion
- provide a reserve of fluid to allow for small leakage
- provide a means of filling and checking the system
- allow a space for trapped air to settle out (in certain systems only)
- provide a means of cooling the fluid when the pump is not under demand
- provide an emergency supply of fluid to a hand pump (in certain systems only).
What are the two types of reservoirs used in aircraft hydraulic systems?
- Non-pressurised
- Pressurised
What are the components of non-pressurised reservoirs (brief description of each)?
- Sight glass = visual identification
- Filler cap = prevent fluid loss or the ingress of contaminants and a means of topping up fluid
- Vent = allows reservoir to breathe
- Filter = provides initial fluid filtration
- Return line = allows fluid to return, angled into a “swirl can”
- Power pump outlet = connected to standpipe at bottom of reservoir
- Hand pump outlet (emergency system) = located at lowest point
Why are reservoirs pressurised?
- Ensure a positive feed of hydraulic fluid to the pumps at all times during high altitude flight
- Prevent the fluid from foaming, thus preventing cavitation
How is a desired pressure range within the reservoir maintained?
- By containing a relief valve that stops the reservoir over-pressurising
What are the two methods used to pressurise reservoirs? Give brief description
- Bleed air from the aircrafts pneumatic system - relief valve fitted to relive excessive pressure if pressure reg fails
Hydraulic pressure - quantity of fluid is indicated by amount the piston protrudes from the body of the reservoir
Single acting and double acting are what?
Types of hand pumps
What is the basic operation of a single acting pump?
When handle is moved toward the right the piston movement creates a low-pressure condition and draws fluid from the reservoir through the check valve into the cylinder. (vice versa for handle moving left)
