TOPIC 1: Hydraulic and Pneumatic Systems Flashcards

1
Q

Pascal’s law states what?

A

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

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2
Q

State the definition of force?

A

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)

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3
Q

State the definition of pressure?

A

Is when a force is applied over a given area (expressed in pounds per square inch, PSI or grams per square inch g/cm2 )

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4
Q

State the definition of work and how is it calculated?

A
  • 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
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5
Q

How is power calculated?

A

FORCEXDISTANCE/TIME

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6
Q

How is mechanical advantage defined?

A

The ratio of output force to the input force applied to a mechanism

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7
Q

What are the two major advantages hydraulic systems has over other types of mechanical systems?

A
  • 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
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8
Q

What functions does the reservoir conduct in regards to the hydraulic system?

A
  • 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).
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9
Q

What are the two types of reservoirs used in aircraft hydraulic systems?

A
  • Non-pressurised
  • Pressurised
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10
Q

What are the components of non-pressurised reservoirs (brief description of each)?

A
  • 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
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11
Q

Why are reservoirs pressurised?

A
  • 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
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12
Q

How is a desired pressure range within the reservoir maintained?

A
  • By containing a relief valve that stops the reservoir over-pressurising
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13
Q

What are the two methods used to pressurise reservoirs? Give brief description

A
  • 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
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14
Q

Single acting and double acting are what?

A

Types of hand pumps

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15
Q

What is the basic operation of a single acting pump?

A

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)

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16
Q

What is the basic operation of a double acting pump?

A
  • Piston moved right increasing pressure in chamber to the right of the piston closing the inlet port check valve
  • As pressure of the chamber diminished with the piston movement, fluid forces the piston check valve open and fluid flows through the piston to the next chamber
17
Q

What power driven pump is driven by the engine via an accessory gearbox?

A

Engine driven pump

18
Q

Why are electric motor driven pumps used?

A
  • Installed for emergencies (i.e. when EDP is inoperative)
  • In some aircrafts they are used to power auxiliary hydraulic systems or to supplement the normal hydraulic power supply
19
Q

What are the four power driven pump categories?

A
  • Gear type, vane type, gerotor type and multi-piston type
20
Q

What power driven pump consists of steel gears, one driven by either the engine or other power unit and the other meshes with the drive gear?

A

Gear pumps

21
Q

What power driven pump consists of a rotor drive shaft and eccentric rotor with sliding vanes?

A

Vane pump

22
Q

What is the basic operation of a vane pump?

A
  • Space between vanes and case fills with oil as it passes the inlet
  • Then is carried towards the outlet
  • As space near outlet diminishes oil is forced out of the pump
  • Downstream resistance to flow will determine oil pressure
23
Q

What power driven pump does the gear ride inside the rotor which rotates freely within the housing?

A

Gerotor

24
Q

What is the basic operation of the gerotor pump?

A

Turned by the accessory drive from the engine and as it turns it rotates the even tooth outer gear rotor

25
Q

What is a fixed delivery multiple-piston pump?

A
  • Deliver a fixed amount of fluid at any given number of revolutions per minute
  • Consists of a drive shaft where pistons are attached, a cylinder block where pistons are inserted and a stationary valving surface
26
Q

What is a variable delivery multiple-piston pump?

A
  • Designed to vary the volume of fluid being delivered at a given number of revolutions per minute
  • Same basic construction of delivery pump and is designed so the alignment of the rotational axis of the cylinder block can be varied
27
Q

What are the types of filter elements in hydraulic systems? Give brief description

A
  • Paper - constructed from specially treated cellulose paper, where fluid flows from outside through the element and then out
  • Sintered metal - comprised of composed metal particles that have undergone a sintering process, where fluid flows through the sides into the center and out
  • Stainless steel - are a one piece wove wire mesh, where the operate same as paper but are reused rather then thrown out
28
Q

What does the filter bowl assembly consist of?

A
  • Filter head
  • Filter case/bowl
  • Filter element
  • By-pass valve
29
Q

What is the different purposes of accumulators?

A
  • Primary purpose = store hydraulic fluid under pressure
  • Act as a cushion or shock absorber
  • Store enough under pressure for emergencies
  • Supplement the hydraulic pump output peak load conditions
30
Q

What does a piston type accumulator consist of?

A

A metal cylinder, a flowing piston, an air or nitrogen charging valve and a hydraulic fluid port

31
Q

What is a diaphragm accumulator constructed of?

A
  • A metal sphere, a synthetic rubber diaphragm, an air or nitrogen valve and a hydraulic fluid port
32
Q

What is a flow control vale?

A

Used to control the flow of a fluid within the system (i.e., water tap, closed = no flow etc.)

32
Q

How can valves by controlled?

A
  • By the pilot directly
  • Electrically or electronically
  • Mechanically
  • Hydraulically
  • Pneumatically
  • A combination of two or more of these methods
33
Q

What is a check valve?

A

Is a non-return valve that allows fluids to flow one direction only

34
Q
A