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Basic Principle of HYD
Blaise Pascal
Linde Material Handling
Instructor Rob Evans
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Basic Principle of HYD
Pascal's (1623 to 1662),
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)
The history of hydraulics started in the 1600,s with Blaise Pascal
who was a French mathematician physicist and inventor
Pascal's work in the fields of the study of hydrodynamics and
hydrostatics centred on the principles of hydraulic fluids. His
inventions include the hydraulic press (using hydraulic pressure to
multiply force) and the syringe.
Pascal's Law comprises a set of principles formulated in 1648 and states that
pressure applied to a confined fluid at any point is transmitted undiminished throughout the
fluid in all directions and acts upon every part of the confining vessel at right angles to its
interior surfaces and equally upon equal areas.
This is the basic principle behind any hydraulic system - pressure applied anywhere to a
body of fluid causes a force to be transmitted equally in all directions, with the force acting
at right angles to any surface in contact with the fluid.
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Basic Principle of HYD
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Joseph Bramah (13 April 1748 – 9 December 1814),
Over 100 years later a British born inventor and locksmith Joseph Bramah invented a
hydraulic press.
Bramah.s hydraulic press depends on Pascal's principle, that pressure throughout a
closed system is constant. The press had two cylinders and pistons of differing crosssectional areas. If a force was exerted on the smaller piston, this would be translated into
a larger force on the larger piston. The difference in the two forces would be proportional
to the difference in area of the two pistons. In effect the cylinders act in a similar way that
a lever is used to increase the force exerted. Bramah was granted a patent for his
hydraulic press in 1795.
Bramah's hydraulic press turned out to have many industrial applications and still does to
this day. At the time hydraulic engineering was an almost unknown science, and Bramah
(with William George Armstrong) was one of the two pioneers in this field.
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Modern Hydraulic Actuation offers many advantages and the following list gives
some of the factors which make it suitable for many applications.
a)
b)
c)
d)
e)
f)
g)
h)
i)
j)
k)
l)
m)
.
n)
Complex controls with mechanical simplicity.
Infinite variety of speeds, which are accurately controlled and
changeable during operation.
Smooth, vibration less action that is little affected by load variations.
Cushioning effect at end of stroke.
Great pressure where needed, with or without motion
High mechanical advantage easily obtainable.
Motion can be linear, rotary or part rotary in any plane.
Self lubricating
Mechanical wearing parts eliminated e.g. clutches, gearboxes.
Safety features and interlock easily incorporated.
High efficiencies obtainable.
Power can be interrupted, reversed, varied almost instantaneously.
Power transmittable to positions inaccessible by mechanical
means.
Constant HP drives and constant torque drives obtainable.
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Basic Principle of HYD
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Applications of Hydraulics
Agricultural
Ship Building
harvesters
stabilisers
tractor Accessories
container handling
Civil Engineering Plant
rudder
excavators
Military vehicles and equipment
bulldozers
barrel elevation
graders
stabilising dozer blade
cranes
recovery vehicles
Injection Moulding Machines
Entertainment
Smelting Plant, foundries and forges
Fair Ground, theme park
Machine tools
rides
presses and roller presses
Stage effects
planing, shaping, milling, drilling
Lifts
and sanding machines
Inspection Ramps
woodworking machines
Commercial vehicles
Aerospace industry
hydraulic handling boom
under carriage bay doors
hydraulic tail board.
radar dishes
flaps and ailerons
And of course
docking equipment
Linde
FORK LIFT TRUCKS
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Basic Principle of HYD
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Applications of Hydraulics in LINDE
Including
attachments
Eg
Lift
Drive
Tilt
Steering
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Basic Principle of
HYD
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Hydraulics falls into two distinct
categories,
Hydrodynamics
hydrodynamics and hydrostatics.
Force = mass x acceleration
A torque converter
A torque converter is modified form of a hydrodynamic fluid
coupling, and like the fluid coupling, is used to transfer rotating
power from a prime mover, such as an internal combustion engine
or electric motor, to a rotating driven load. As with the fluid
coupling, the torque converter takes the place of a mechanical
clutch. Unlike a fluid coupling, however, a torque converter is able
to multiply torque when there is a substantial difference between
input and output rotational speed, thus providing the equivalent of
a reduction gear. The most widespread usage of torque converters
is in automobile, bus and light truck automatic transmissions.
Torque converters are also found in marine propulsion systems
and industrial applications.
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Basic Principle of HYD
Hydrostatics
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Hydrostatics
Force = pressure x
area
In a hydrostatic device, power is transmitted by
pushing a confined liquid . The liquid most
move/flow to cause motion
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Basic Principle of HYD
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Hydrostatics
We come across a large scale HYDROSTATIC system every day in our water supply
Water towers are tall to provide pressure. Each foot of
height provides 0.43 PSI (pounds per square Inch) of
pressure. A typical municipal water supply runs at
between 50 and 100 PSI (major appliances require at
least 20 to 30 PSI). The water tower must be tall enough
to supply that level of pressure to all of the houses and
businesses in the area of the tower. So water towers are
typically located on high ground, and they are tall enough
to provide the necessary pressure. In hilly regions, a
tower can sometimes be replaced by a simple tank
located on the highest hill in the area.
PUMP
Outlet
50 to 100 psi
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Basic Principle of HYD
Pascal's
Law
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Pascal's law states that when there is an increase in pressure at any point in a confined fluid,
there is an equal increase at every other point in the container.
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Pascals Law
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If we use Pascal law and formal P = F/A we can calculate the pressure in this tank
Pressure =
Force applied
2400 N
Piston AREA
20 cm2
Force applied = 2400 Newton's
Piston Area = 20
Page 11Pressure
cm2
F
Pressure = 120 N/cm2
= 12 Bar
?
is applied in all directions and acts with equal force on equal
areas
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Basic Principle of HYD
Pascals Law
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If we use Pascal law and formal P = F/A we can calculate the pressure in this tank
Pressure =
Force applied
2400 N
Piston AREA
20 cm2
Force applied = 2400 Newton's
Piston Area = 20
1 Bar
1 Bar
cm2
=
=
Pressure = 120 N/cm2
F
2
1000,000N/m
?
(Pascal)
2
10 N/cm
(Newtons per centimeter )
2
1 Bar
=
1Kgf/cm
1 Bar
=
14.5 Psi
Page 11Pressure
= 12 Bar
(Kilogram-force per square centimetre )
(Pounds per Square Inch )
is applied in all directions and acts with equal force on equal
areas
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hydrostatic paradox of controversy
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An even more striking paradox is that associated with the horizontal pressures on a dam. Consider Figure 3a, which shows a stylized version of the
Hoover dam holding back Lake Mead.
The lake is about 115 miles long and at the dam is about 600 feet deep. Near the dam's base the horizontal thrust is about 18 tons per square foot.
Now have a look at Figure 3b, which shows the same dam holding back Lake Mudd, which is only 115 inches long.
Here's the paradox: in both cases, the horizontal thrust on the dam is the SAME
" . . . the hydrostatic paradox of controversy. Don't you know what that means? Well, I will tell you. You know
that, if you had a bent tube, one arm of which was of the size of a pipe-stem, and the other big enough to hold
the ocean, water would stand at the same height in one as in the other. Controversy equalizes fools and wise
men in the same way. And the fools know it."
Holmes, Oliver Wendell
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Basic Principle of
HYD
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We Can use
F
P A
: - area
Pressure = Force
Force
Area
= Pressure x
:
Area = Force Pressure
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F
PA
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: - area
Pressure = Force
100 N
Force 100N/cm
Area
2 cm2
= Pressure 25 N/cm
4 cm
2.5 bar
50
0 100
4 cm2
1 Bar
=
Pressure
10 N/cm
=2.5?
Bar
(Newton's per centimetre
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F
PA
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100 N
100 N
Pressure = Force - area
Force 200N/cm
Area
2 cm
= Pressure 25 N/cm
8 cm
2 cm
2.5 bar
50
0 100
Pressure
4 cm
=2.5?
Bar
4 cm
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F
PA
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150 N
100 N
50
2 cm
2 cm
0 100
50
0 100
4 cm
4 cm
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Find pressure of cylinder one first
P
=
F
…..
/
A
….
P = ……
To find pressure of cylinder two convert pressure of cylinder
one in to force using formula F = P x A
Remembering to deduct the size of the rod from the area of the
cylinder first
F
=
P
…..
x
A
……
F = …….
With the total Force found find the pressure on cylinder 2 two
using
P = F/ A
P
=
F
…..
/
A
….
P = ……
Convert to Bar
P = …… Bar
1 Bar
= 10 N/cm (Newton’s per centimetre )
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F
PA
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320 N
100 N
50
6 cm
10 cm
0 100
50
0 100
10 cm
20 cm
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Find pressure of cylinder one first
P
=
F
…..
/
A
….
P = ……
To find pressure of cylinder two convert pressure of cylinder
one in to force using formula F = P x A
Remembering to deduct the size of the rod from the area of the
cylinder first
F
=
P
…..
x
A
……
F = …….
With the total Force found find the pressure on cylinder 2 two
using
P = F/ A
P
=
F
…..
/
A
….
P = ……
Convert to Bar
P = …… Bar
1 Bar
= 10 N/cm (Newton’s per centimetre )
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Basic Principle of HYD
Pascal's
Law
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In addition to Pascals law, the following should always be remembered when
dealing with Hydraulics
1 Fluids under pressure always take the line of least resistance
2 A pump creates FLOW not PRESSURE
3 PRESSURE can only build up when there is resistance to flow
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If we fill this pipe( which has the end sealed) with oil and measure the pressure at
three points
What reading would we expect
Pressure due to
‘head’ of liquid.
50
50
50
0 100
0 100
0 100
No movement of liquid therefore pressure is the same
throughout
(the oil is not WORKING)
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If we add a pump ,a actuator and a ram
What would be the pressures at the three gauges
(the oil is now flowing)
Ram
50
50
50
0 100
0 100
0 100
Actuator
Pump
Liquid flowing - always flows from high pressure to lower pressure - pressure drop in
direction of flow
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Pipe Size Nomogram
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Flow Velocity
400
300
Metres/sec.
200
Ft./sec.
150
Recomm. Range
for Suction
& Return
Line
100
50
40
Flow
L/min
30
Flow
Gal/min
20
15
10
BoreMillimetres
Recomm. Range
Pressure
Line
Bore
Inches
5
4
3
2
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Pipe Size Nomogram
Heat
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High Temperatures:-
Excessively high oil temperatures have the following effects:Firstly, due to the oil being thinner, its function as a lubricant is reduced and wear may
be increased.
Secondly, the rate of deterioration of the oil and formation of contaminants is
increased.
Thirdly, due again to oil being thin, internal leakage in pumps and valves is increased
and the efficiency of the hydraulic system is reduced.
The following table gives a guide to working temperatures of oil:Temperature in F
Working Conditions
Up to 115 (45 C)
Ideal working conditions.
115 to 130 (45-55 C)
Still in safe range.
130 to 150 (55-65 C)
Shortened oil life expected.
Linde working temp is
60 C
to
80  C
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Fitting of pipe work
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Fitting of pipe work
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Basic Principle of HYD
Pipe Size Nomogram
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Flow Velocity
Using the Pipe size chart work out the
400
300
Metres/sec.
200
150
Ft./sec.
pipe size for this attachment
Recomm. Range
for Suction
& Return
Line
100
50
40
Flow
L/min
30
Flow
Gal/min
20
15
10
BoreMillimetres
Recomm. Range
Pressure
Line
Bore
Inches
5
4
3
2
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Basic Principle of HYD
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Flow Velocity
400
300
Metres/sec.
200
Ft./sec.
150
Recomm. Range
for Suction
& Return
Line
100
50
40
Flow
L/min
30
Flow
Gal/min
20
15
Recommend
flow 29 L/min
10
BoreMillimetres
Recomm. Range
Pressure
Line
Bore
Inches
5
4
3
Pipe size 12mm
2
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Basic Principle of HYD
Types of
Flow
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LAMINAR FLOW
This type of flow occurs in smooth tubes and at LOW flow rates.
The flow is streamlined and there is no turbulence. The flow occurs in parallel layers,
with minimal disruption between these layers.
The flow is greatest at the centre and diminishes towards the periphery. This makes
the laminar flow describe a bullet shaped "velocity profile" shown in red below:
Direction of flow
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Types of
Flow
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TURBULENT FLOW
This type of flow occurs in rough tubes and at higher flow rates.
The flow is not streamlined. There is a lot of swirling (eddies) of the fluid.
The flow is not greatest at the centre. Thus, as shown in red below, the "velocity
profile" of turbulent flow is more flat than that caused by laminar flow.
Direction of flow
Turbulent flow needs more pressure to drive it. For a given pressure
difference, you will have a lesser flow with turbulent flow than with laminar
flow.
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Types of
Flow
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Certain factors favour the changing of laminar flow to turbulent flow.
velocity, Use the correct pump for correct flow
density,
The density of Water is 1.0 or 1000Kg/m3 The density for Oil is 0.8 or 800Kg/m3
diameter, Using the correct size of pipe for the flow (not to many Bends or restrictions )
Viscosity oil's thickness, or viscosity. A thin oil has a lower number (eg:, ISO VG 32) and flows
more
easily
Direction of flow
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Basic Principle of HYD
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How to measure volumetric flow
•
•
Bucket-and-stopwatch
Perhaps the simplest way to measure volumetric flow is to measure how long it takes to fill a known volume
container. A simple example is using a bucket of known volume, filled by a fluid. The stopwatch is started when the
flow starts, and stopped when the bucket overflows. The volume divided by the time gives the flow. The bucketand-stopwatch method is an off-line method, meaning that the measurement cannot be taken without interrupting
the normal flow.
Linde 386 E20P
The delivery output of the hydraulic pump varies
depending on the vehicle model:
• 24 V-vehicles − delivery output 9 cm3
• 48 V-vehicles − delivery output 11 cm3
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Basic Principle of HYD
How to measure volumetric flow
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Turbine flow meter
The turbine flow meter (better described as an axial turbine) translates the
mechanical action of the turbine rotating in the liquid flow around an axis into a userreadable rate of flow The turbine tends to have all the flow travelling around it.
The turbine wheel is set in the path of a fluid stream. The flowing fluid impinges on
the turbine blades, imparting a force to the blade surface and setting the rotor in
motion. When a steady rotation speed has been reached, the speed is proportional
to fluid velocity.
Turbine flow meters are used for the measurement of liquid flow
KEM HM 007/U* Hydraulic Oil Turbine
Flow Meter
1.2–20 l/min
Max 400 Bar Aluminium body
1/4" BSPf Connections
Coil Signal Output
(Amplified pulse & 4 to 20 mA available,
See options)
Details
SKU
HM 007/U*
Datash
eet:
Price:
UK£847.00 (excl. VAT)
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Basic Principle of HYD
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How to measure Pressure
Glycerine filled, all stainless steel, surface mounted with vertical connection
A heavy duty bourdon tube pressure gauge suitable for a wide range of applications,
glycerine filled for a dampening effect on vibration and pressure surges.
Available in dial size 100mm
Pressure ranges from -1 bar to 1400 bar (20,000 P.S.I.)
All stainless steel construction
Glycerine filled for a dampening
effect on vibration & pressure
surges
Linde Test Kit
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Basic Principle of HYD
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Hydraulics' in operation
WE use a very simple hydraulic circuit /system in our industry every
day
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Basic
Principle of HYD
Service
Hydraulics'
Training in operation
The problem with this system is we can only
“jack” the vehicle up with one stroke of the lever
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PUMP
ACTUATOR
137
Basic
Principle of HYDTo Make the car JACK work efficiently
Service
Hydraulics'
Training in operation
we have to fit more
components to the circuit
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PUMP
ACTUATOR
2
38
Basic
Principle of HYDTo Make the car JACK work efficiently
Service
Hydraulics'
Training in operation
we have to fit more
components to the circuit
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1x Hydraulic tank
2 x Non Return Valve
Hydraulic
tank
Non Return Valve
PUMP
Non Return Valve
ACTUATOR
3
39
Basic
Principle of HYDTo Make the car JACK work efficiently
Service
Hydraulics'
Training in operation
we have to fit more
components to the circuit
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1x Hydraulic tank
2 x Non Return Valve
Hydraulic
tank
Non Return Valve
PUMP
Non Return Valve
ACTUATOR
4
40
Basic
Principle of HYDTo Make the car JACK work efficiently
Service
Hydraulics'
Training in operation
we have to fit more
components to the circuit
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1x Hydraulic tank
2 x Non Return Valve
Hydraulic
tank
Non Return Valve
PUMP
Non Return Valve
ACTUATOR
541
Basic
Principle of HYD To Unable the engineer to
Service
Hydraulics'
Training in operation
lower the vehicle A “tap”
must be fitted
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Hydraulic
tank
Non Return Valve
PUMP
Non Return Valve
ACTUATOR
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Basic Principle of HYD
operation
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operation
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