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Semester 2 2024 > MECHENG236 Hydraulics/Pneumatics > Flashcards

MECHENG236 Hydraulics/Pneumatics Flashcards

1
Q

What are fluid power systems?

A

Use a working fluid to transmit power and motion, no solid linkage

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2
Q

How is power transmitted in a fluid power system?

A

Conservation of mass, pascal’s law

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3
Q

Hydraulic inputs (Power sources)

A

Pumps, accumulators

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4
Q

Hydraulic outputs

A

Actuators: Linear, rotary

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5
Q

Hydraulic middle (control)

A

Valves: Rate, pressure, direction

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6
Q

Fluid power system advantages

A

Advantages
* Fluid easy to transport
* Components mechanically
simple
* Distribute pressure source
from actuator
* Low explosion risk*
* Variable Speed
* Pneumatics – air is
everywhere

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7
Q

Fluid power system disadvantages

A

Disadvantages
* Contamination
* Risk of leaks
* Gases are compressible
* Restricted forces
* Can be loud

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8
Q

Hydraulic advantages

A

Little energy
absorption by fluid
* Higher forces

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9
Q

Hydraulic disadvantages

A
  • Oil may be
    flammable
  • Heavy
    components due to
    pressure
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10
Q

Pneumatic advantages

A
  • Fewer shock loads
  • Lighter weight
  • Air easily available
  • Reliable
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11
Q

Pneumatic disadvantages

A
  • Lower loads
  • Energy stored in
    fluid may be rapidly
    released if leak
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12
Q

Are hydraulic and/or pneumatics compressible

A

Gas working fluid is compressible

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13
Q

Working fluid of hydraulics/pneumatics

A

Hydraulics: Liquid (water, oils)
Pneumatics: Gas (air)

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14
Q

Role of pumps

A

Add pressure to the flow, convert work to pressure

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15
Q

2 types of pumps

A

Positive displacement (PDP)
Dynamic

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16
Q

PDP pumps

A

Forced volume change
Pulsating, irregular flow
Very high pressures

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17
Q

Dynamic pumps

A

Momentum added
Smooth, fast flows
Lower pressures

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18
Q

Three types of positive displacement pumps

A

Gear
Vane
Piston

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19
Q

Gear pumps teeth relationship

A
  • Fewer, bigger teeth = stronger,
    but more
    pulsating
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20
Q

Gear pumps adv/disadv

A

Advantages
* Low complexity, cost
* Compact
* Can handle high-viscosity fluids
Disadvantages
* Pressure and flow rate cannot be changed independently
* Abrasives wear teeth
* Sealing and losses

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21
Q

Vane pump adv/disadv

A

Advantages
* High pressures for low-viscosity fluids
* Good intake suction
Disadvantages
* Complex
* Pressure and flow rate cannot
be changed independently
* Not suitable for high viscosity
fluids

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22
Q

Types of piston pumps

A

Single Piston
Multi-piston
Swash Plate

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23
Q

Swash Plate adv/disadv

A

Advantages
* Large pressure range
* Pressure and flow rate can be independently controlled
* Wide viscosity range
Disadvantages
* Complex
* Tight tolerances
* Bulky

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24
Q

Accumulators

A

Store pressure, an energy reserve

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25
Q

Uses of accumulators

A

Emergency pressure supply
Smoothing peak loads

26
Q

Types of actuators

A

Motor (continuous rotational motion)
Rotary and Semi-rotary (limited rotational motion)
Linear (hydraulic cylinder)

27
Q

Rotary actuators compared to motors

A

Simpler
Cannot over-extend

28
Q

Common rotary actuator

A

Vane-type

29
Q

Semi-rotary actuators

A

Produce limited rotational motion from internal linear motion

30
Q

Benefit of semi-rotary actuators over rotary actuators

A

Easier to stop and hold

31
Q

Motor actuator adv/disadv

A

Adv: Large angle
range, can use
as pump
(some)
Disadv: More
complicated,
expensive

32
Q

Rotary actuator adv/disadv

A

Adv: Simpler, cannot
over-extend
Disadv: Best for end-
to-end or
oscillatory
applications

33
Q

Semi-rotary adv/disadv

A

Adv: Simpler, cannot
over-extend,
“stop-and-
hold”
Disadv: More
complicated
than rotary

34
Q

Linear actuators retraction types

A

Single-acting: Hydraulic pressure acts on one side only
Double-acting: Hydraulic pressure acts on both sides of the piston

35
Q

Double-ended linear actuators

A

Piston rod out both ends of casing
-equal surface area for extension and retraction

36
Q

Cushioned linear actuators

A

Flow restricted on piston head
Increases back pressure near end of stroke
Reduces flow rate, slows piston
Prevents abrupt end to motion, less damage risk

37
Q

What do pressure converters do? (also known as pressure intensifiers or pressure de-intensifiers)

A

Provide pressure change between input and output
- change proportional to area

38
Q

Pressure converter use cases

A

Meeting high pressure when low pressure available
Can use dissimilar fluids
Limited by length of stroke
Increase pressure - reduce flow volume

39
Q

What do control valves enable and control

A

More complicated, safer circuits
Control: Pressure, flow, direction

40
Q

Purpose of pressure control

A

Enable excess pressure to be bled
Provide different pressures to different components

41
Q

How are pressure control valves controlled

A

Springs
Pilot Pressure

42
Q

Types of pressure relief valves

A

Single-stage relief valves (also known as direct acting or check valves)
-Max pressure set by spring compression
Variant - pilot (sample) pressure line pushes spool. Spring does not resist bulk flow (can be weaker, cheaper)
Multi-stage

43
Q

Direct vs two stage valves

A

Direct: Simple, compact, low cost. Suffer hysteresis, losses: If weak spring starts to open at low pressures = hysteresis, losses. If strong spring: starts to open nearer target pressure, does not open far enough (hazard)

Two stage valves: Combine two valves, one sampling pilot, one on main line. More complex but less hysteresis. Important for narrow-band pressure response on sensitive components.

44
Q

Pressure reducing valve

A

Reduce pressure to a set value

45
Q

Differential pressure regulator

A

Reduce pressure by a set value

46
Q

Proportioning pressure regulator

A

Reduce pressure by a fixed ratio

47
Q

Pressure reducing valve operation

A

Maintains constant output pressure. Pilot on outflow. If pilot pressure exceeds spring-set target, spool shifts, blocking flow.

48
Q

Differential pressure regulators operation

A

Maintain constant pressure difference. Pilot pressure on inflow and outflow. Use a spring to ensure constant pressure difference

49
Q

Proportioning pressure regulator operation

A

Maintain constant pressure ratio
Pilot pressure on inflow and outflow
Uses area ratio on pilot pressures

50
Q

How is flow controlled?

A

Ideally would vary flow rate at pump.
If cannot, or have branches, need flow control valve.
Introduce flow restriction, slow flow.
Combine with non-return valve, reduce flow only one way, free the other.

51
Q

Types of direction control valves

A

Flow dividers - split flow into two or more parts, flow constrictors control proportions

Non-return (check) valves - prevent flow in one direction

52
Q

Where are non-return valves often located?

A

Downstream of pumps (along with relief valves)

53
Q

Counterbalance valves

A

Combines non-return valves and pressure control valve
-free flow in one direction, set back pressure the other

54
Q

Multi-way directional control valve label meanings

A

4/2
4 connections (ports)
2 positions (ways)

55
Q

Categories for controlling control valves

A

-Mechanical
-Pneumatic
-Hydraulic
-Electrical

56
Q

Shape of filters and purpose

A

Cylindrical, maximise filter area, minimise pressure drop
Replace regularly
Debris enters through open vents, can damage components, clog pipes

57
Q

Places to put filters

A
  • Before reservoirs
  • Before pump
  • Before vent
58
Q

Additional control components

A
  • Provide human monitoring (gauges)
  • Provide human control (switches)
59
Q

Miscellaneous components

A

Pipes (rigid)
Hoses (flexible)
Fittings (binds hoses and pipes together)
Connectors (adapters, connect pipes and fittings to specific components)

60
Q
A

Semester 2 2024 (17 decks)

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