Transcript No Slide Title

Basic Principles of Hydraulics
Symbols
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Symbols
Pumps
Fixed Displacement
One direction of flow. Constant delivery for constant speed
Variable Displacement
One direction of flow. Variable delivery for constant speed
Pressure compensated variable pump
One direction of flow, adjustable spring and pump case drain.
Method of adjustment is shown on the arrow
Directional of flow reversible. Variable delivery for constant speed.
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Hydraulic Energy Source
(simplified representation)
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Symbols
Drive units
Motors
Fixed Displacement
M
Electric Motor
M
Engine
One direction of rotation. Constant shaft speed
for constant flow rate
Either direction of rotation, depending on direction of flow.
Constant shaft speed for constant flow rate.
Variable Displacement
Either direction of rotation. Speed variable for
constant flow.
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Symbols
Semi rotary actuator
Limited rotary movement eg 1800
Pressure Intensifiers
Equipment to transform
a pressure x in to a
pressure y
Single acting
x y
Continuous
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Symbols
Actuators
Single Acting
Returned by external force
Spring return
Vent
Telescopic Cylinder
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Symbols
Actuators
Double acting
Forward and return stroke under power
Single piston rod.
Double acting
Double ended piston rod
Variable cushioning at both ends.
Cushioned
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Symbols
Directional Control Valves
A
Two Way
Porting
(2 position)
P
2/2 way valve
Normally closed
A
Three Way
P
T
A
B
Four Way
P
T
3/2 way valve
Normally closed
4/2 way valve
Changeover
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Valve Description
Number of Ports
3
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Valve Description
Number of Ports
3
Number of Control
positions
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Valve Description
Number of Ports
3
Number of Control positions
2
(Number of Boxes)
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Valve Description
Number of Ports
3
Number of Control positions
2
(Number of Boxes)
Method of
Operation
Push
Button
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Valve Description
Number of Ports
3
Number of Control positions
2
(Number of Boxes)
Method of
Operation
Push
Button
Method of
Return
Spring
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Valve Description
Number of Ports
3
Number of Control
positions
2
(Number of Boxes)
Flow path blocked
when valve is at rest
Flow path open when
valve is at rest
Method of
Operation
Push
Button
Method of
Return
Spring
Normally closed
or Normally open
Normally
Closed
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Symbols
Directional Control Valves
A
B
Closed centre
3 position valves
P
T
A
B
Open centre
P
T
A
B
Tandem centre
P
T
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Symbols
Directional Control Valves
A
B
3 position valves
Floating Centre
P
T
A
B
Regenerative Centre
P
T
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Symbols
Methods of Operation
General manual operation
Usually used to represent a manual override
Lever operation
Foot Pedal operation
Push Button operation
Detent operation
Usually used with lever operation
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Symbols
Methods of Operation
Pilot operation
Roller operation
Spring operation
Usually used as a return or centring function
Solenoid operation
Internal pilot or 2 stage operation
Usually used with solenoid operation
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Symbols
Non return valves
Opens if inlet pressure is higher than outlet
pressure
Free
Spring loaded
Opens if inlet pressure is higher than outlet
pressure plus spring load
Pilot operated
Can be opened to permit reverse flow by means of
pilot pressure
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Symbols
Pressure Controls
Single stage with internal drain
Pressure Relief Valve
Also sometimes represented so
With external drain
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Symbols
Pressure Controls
Pressure Relief Valve
Remote pilot control with internal drain
Internally piloted or 2 stage relief valve
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Symbols
Pressure Controls
A
Pressure Regulating Valves
Downstream pressure control Forward flow
only external drain
B
Downstream pressure control.
If outlet pressure exceeds set pressure, flow is
diverted to tank.
3 way pressure regulating valve
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Symbols
Pressure Controls
Pressure regulator with reverse flow by-pass built
in
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Symbols
Comparison
Pressure Controls
Pressure Relief
Pressure Regulator
Pressure operation from
inlet
Shown normally closed
A
Pressure operation from
outlet
Valve is closed until the pressure at the inlet is high enough
to open it (set pressure). Flow is then usually to tank.
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B
Shown normally open
Valve is open until the pressure at the outlet is high enough to
close it (set pressure). Flow is usually to cylinder or other part of
the circuit.
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Symbols
Pressure Controls
Sequence Valves
Maintains upstream pressure, allows flow through
to other functions.
Two stage sequence valve
Maintains upstream pressure, allows flow through
to other functions.
External drain
Provides controlled backpressure for load support.
With built in by-pass
Counterbalance valve
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Symbols
Flow Controls
Flow proportional to preset area times the square root of the
pressure drop across restrictor
Non pressure compensated
Flow restricted in one direction only.
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Symbols
Flow Controls
Flow proportional to preset area irrespective of valve
pressure drop. Direction of flow as indicated (non
reversible). Excess flow must find alternative path.
Pressure Compensated
Also sometimes
Pressure & Temperature
Compensated
Preset area automatically adjusts to compensate
for viscosity changes
Bypass Regulator
Excess flow bypassed internally
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Symbols
Flow Controls
Input flow is divided to 2 flows of fixed ratio
Pressure compensated.
Flow divider
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Symbols
Proportional Valves
Valve with 2 distinct operating positions, fully open and fully
closed, and an infinite number of intermediate positions.
4/3 directional control valve, proportional.
3 distinct operating positions with closed centre position and an
infinite number of intermediate positions.
Solenoid current is controlled through proportional amplifier.
Servo valve
Controlled by a torque motor.
Direction of movement is dependent on voltage polarity.
Amount of movement is dependent on magnitude of current.
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Symbols
Modulating Control Valves
More often referred to as Proportional Control Valves and usually solenoid operated.
With these valves there is a known relationship between the position of the spool and the flow through the valve. Therefore flow
(speed) can be controlled electronically without the need for adjusting manual valves.
Full flow
Proportional Valve
Flow
Rate
Conventional valve
Spool Travel
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Symbols
Miscellaneous
Vented to atmosphere
Reservoirs
Return line below fluid level
Return line above fluid level
Header tank
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Symbols
Miscellaneous
Conditioning Units
Filter or Strainer
Cooler
Water cooled
Heater
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Symbols
Miscellaneous
Pressure Gauge
Shut off valve
Accumulator
Gas type
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Hydraulic Formulae
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Hydraulic Formula
Force
Newtons
Pounds
(F)
(N)
(lbf)
=
Area (A)
x
Square metres (sq. m)
Square inches (sq. in)
Pressure (P)
Pascals (Pa)
Pounds/sq.in (psi)
Note:
* The pascal is a very small unit of pressure.
100 Kpa
=
e.g.
5000KPa
F = A x P
10N
cm2
=
14.5 psi
=
1 Bar
=
50 Bar
=
725 psi
P = F
A
-------------------------------------
A = F
P
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Hydraulic Formula
Flow Rate =
metres 3 / sec
Flow Velocity
x
metres / second
Flow area
metres 2
Usually flow rate is given in Litres/minute and flow area given in cm2 or mm2 .
Care must be taken to ensure the correct multiples are used.
Eg. Calculate the cross sectional area required for the suction line of a pump delivering
40 l/min with a maximum flow velocity of 1.2 m/s.
40 l/min = 40/60 x 10-3 m3/s
Area
=
Flow velocity
Flow rate
Area
=
40 x 10 -3
60 x 1.2
Area
=
0.555 x 10 -3 m2
m2
(Pipe bore of 26.6mm)
--------------------------------------------------------------------------
Volume of cylinder (base end)
=
Piston area x stroke length
Volume of cylinder (rod end)
=
(Piston area - Rod area) x stroke length
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Hydraulic Formula
Work done
=
Force
x
distance moved
Force on a piston
So,
work done
=
Pressure
x
area of piston
=
Pressure
x area x distance moved
Area x distance moved =
Volume
So
Work done
=
Pressure
x
volume
Power is the rate of doing work or, work done per unit of time.
Volume per unit time is flow rate - m3/second
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Hydraulic Formula
So
Hydraulic power
=
Pressure
x
Flow rate
If pressure is in Pascals (N/m2) and the flow rate is in m3/second then
Hydraulic power
=
Pressure
x
Flow rate -
(Nm/s) = Watts
It is usual to give flow rate in litres/minute and pressure in bars. To use these units in the calculation the following
conversion has to be made.
Hydraulic Power (kW)
=
Pressure (bar)
x
Flow rate (l/min)
600
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1) If a system pressure of 3000 p.s.i acts on a piston area of 3 sq ins, (approx 2 ins
produced?
diameter) what force will be
2) If a force of 10,000 lb is produced from a cylinder with a piston area of 2.5 sq ins, what is
system?
the pressure build up in the
3) If a force of 15,000 Newtons is produced in a cylinder with a piston area of 20 sq cm, what
system?
is the pressure build up in the
4) A cylinder with piston area 150 sq cm and stroke length of 400cm must fully extend in 15
Litres/min) must the pump deliver to achieve this?
seconds. What flow rate (in
5) If a hydraulic pump is delivering a flow of 40 litres / min against a pressure of 150 bar, what
KW) at the pump?
is the power consumption (in
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