The fluid discharged by the pump is directed to the ‘hydraulic actuator’.Theactuatorconvertthepressureenergyofthefluid into mechanical energy. There are 3 basic type of hydraulic actuator.
• Theactuatorsconvertthefluidpressuretoasuitablelinearor rotary motion.
• Linearmotion–Hydrauliccylinder
• Rotary motion – Hydro motor
• Rotarymotion–Semi-rotaryactuator
2. Mohammad Azam Khan
HYDRAULIC ACTUATORS
Actuators 2
• The fluid dischargedby the pump is directedto the ‘hydraulic
actuator’.The actuator convert the pressure energy of the fluid into
mechanical energy.There are 3 basic type of hydraulic actuator.
• The actuators convert the fluid pressure to a suitable linear or rotary
motion.
• Linear motion – Hydraulic cylinder
• Rotary motion – Hydro motor
• Rotary motion – Semi-rotaryactuator
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HYDRAULIC CYLINDERS
• A hydraulic cylinder is a device, which converts fluid power into
linear mechanical force and motion. It usually consists of a movable
element, a piston and a piston rod operating within a cylindrical
bore.
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PARTS OF A HYDRAULIC
CYLINDER
• A hydraulic cylinder consists of the following parts
• Cylinder barrel
• Piston
• Piston rod
• Bush
• Cylinder head and cap
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TYPE OF HYDRAULIC
CYLINDER
Hydraulic
cylinder
Single acting
cylinders
Double acting
cylinders
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SINGLE ACTING CYLINDER
• In the case of a single actingcylinder, only the pistonside is pressurized
with hydraulic fluid.The cylinder can thus carry out work only in one
direction.
• The fluid which flows into the piston chamber causes a pressure to build
up the surface of the piston.
• The piston travels into its forward end position.The return stroke is
effectedby a spring, the dead weight of the piston rod or an external
load
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PLUNGER TYPE SINGLE
ACTING CYLINDER
• In the case of plunger cylinders,the pistonand
rod form a single component.
• Due to the design of the cylinder, the return
stroke can only be effectedby external forces.
The cylinders can therefore generallybe
installedonly vertically.
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DOUBLE ACTING CYLINDERS
• In the case of double acting cylinders, both piston surfaces can be
pressurized. A working movement can thus be performed in both
directions.
• With double acting cylinders with a single-sidedpistonrod, different
forces and speeds are obtained on the advance and returnstrokes due
to the difference in area between the piston surface and annular
piston surface.
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DOUBLE ACTING CYLINDER WITH
END POSITION CUSHIONING
• Cylinder with end position cushioningare used to brake high stroke speeds
smoothlyand prevent hard impacts at the end of the stroke. Shortly before
the end position is reached, the cross- sectionfor the outflow of fluidis
reduced by the built-in cushioningpistons and then finallyclosed.The
hydraulic fluid is then forced to escape through a flow control valve.
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END POSITION CUSHIONING
• The piston is a short distance
before its end position; the
hydraulic fluid on the piston- rod
side must escape via the
adjustable flow control valve
above the piston rod
• This type of end position
cushioning is used for stroke
speed between 6 m/min and 20
m/min. At higher speed,
additional cushioning or braking
devices must be used
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END POSITION CUSHIONING
• The piston rod is on its returnstroke;
in this flow direction,the non-return
valve below the pistonrod is
opened, thus by-passing the flow
control valve.The pistonrod retracts
at maximum speed.
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TELESCOPIC CYLINDER
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• Often cylinder & rod length does not fit in the machine. In that case
the piston rod is also used as a piston barrel and a second piston rod is
used.
• These kinds of cylinders are called telescopic cylinders. If we call a
normal rod cylinder single stage, telescopic cylinders are multi-stage
units of two, three, four, five or more stages.
• In general telescopic cylinders are much more expensive than normal
cylinders. Most telescopic cylinders are single acting (push). Double
acting telescopic cylinders must be specially designed and
manufactured.
