The document provides a detailed overview of hydraulic actuators, specifically focusing on linear actuators and cylinder mountings. It categorizes hydraulic actuators into three types: hydraulic cylinders (linear actuators), hydraulic motors (rotary actuators), and limited rotary actuators, and describes their construction and working principles. Various types of hydraulic cylinders, including single acting, double acting, tandem, and telescopic cylinders, are elaborated upon, highlighting their functionalities and applications in engineering.

1. INDUSTRIAL HYDRAULICS
& PNEUMATICS
REPORT ON LINEAR ACTUATORS
& CYLINDER MOUNTINGS
1
PURVESH D. SHINDE
ME 6A
175054

2. ACTUATORS
Hydraulic actuators are the devices which convert the power of
pressurised hydraulic oil (pump does this task of pressurising the oil)
into useful mechanical work. The useful work is obtained through force
and motion of actuator.
Hydraulic actuators are broadly classified into three categories:
i. Hydraulic cylinders also known as linear actuator (or linear
motors).
ii. Hydraulic motors also known as rotary actuators.
iii. Limited rotary actuators.
• Hydraulic Cylinders (Linear actuators): It is a device which converts
fluid power (power of pressurised hydraulic oil) into linear
mechanical force and motion. This motion is generally is linear
direction and we can use this motion with force for carrying out
operations like pushing, pulling etc.
• Hydraulic Motor: It is a device which converts fluid power into
rotary mechanical energy. The rotations created by this energy can
be used for winding/rewinding operations and many tasks in
almost all engineering fields.
• Limited Rotary Actuators: These create half or actions. Now we
will see construction and working of all types of actuators.
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3. Following are the types of hydraulic cylinders:
(i) Single Acting Single Piston Rod Cylinder (SA Cylinder).
(ii) Single Acting RAM.
(iii) Double Acting Single Piston Rod Cylinder (DA Cylinder).
(iv) Double Acting Double Piston Rod Cylinder.
(v) Tandem Cylinder.
(vi) Telescopic Cylinder.
(i) Single acting cylinder
(iii) Double acting
Cylinder
(v) Tandem cylinder
(ii) Single acting RAM
(iv) Double acting
cylinder with double
piston rod
(vi) Telescopic cylinder
Linear actuators (Hydraulic Cylinders)
LINEAR ACTUATORS
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4. Construction: The single acting cylinder is shown in above Fig. 2.21. It
consists of cylinder body in which cylinder bore is created. The inside
surface is machined with close tolerances and is having high finish.
Piston reciprocates in the bore. On backside of piston, compression
spring is used around the piston rod.
Working: Pressurized oil enters into the cylinder through port P. The
pressure force (F = p x a) will push the piston towards right side
thereby compressing the spring. This is the power stroke. Then the
flow of oil stops. Then naturally compressed spring will expand and
push the piston from right to left. During this movement of piston used
oil is pushed out through port 'P' and the oil then returns to oil tank
via filter.
Now again the pressurised oil enters into cylinder the
through port P and the cycle repeats.
o During power stroke, useful work is done at the end of piston rod,
viz. pushing the load.
o This cylinder is having applications in sequencing circuit (Refer
Chapter 3) or in clamping the work piece.
SINGLE ACTING CYLINDER WITH SINGLE PISTON ROD
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5. Construction: It consists of Big Plunger or RAM. It does not have
separate piston and piston rod. RAM is a single body and its piston end
is out of cylinder block. The load is kept on the piston end only. Piston
itself is big and having uniform diameter to avoid buckling.
Working: Pressurized oil comes into the cylinder bore through port 'A'.
During this, port 'B' is closed. The pressurised oil starts occupying the
space in the cylinder and due to pressure force, RAM starts moving
upwards, thereby raising the load.
Now when RAM attains required height, the oil flow through port 'A'
stops and this port is closed. Port 'B' opens, used oil goes out. The
RAM comes down as oil goes out.
This type of hydraulic RAM is used on shipyards to raise and lower the
loads while loading it on cargo ships. This RAM is also used in material
handling equipments used in stacking.
SINGLE ACTING RAM
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6. Construction: It consists of a cylinder body in which piston with single
piston rod can reciprocate. Similar to single acting cylinder, the cylinder
bore is highly finished surface having close tolerances. There are two
ports 'A' and 'B' as shown.
Working: The pressurised oil enters through port 'A'. Due to pressure
force created by oil, piston will move towards right. When piston reaches
'right dead centre', flow through port 'A‘ stops and now pressurised oil
starts entering into piston rod side of cylinder through port 'B'. Due to
pressure force created by oil, piston will start moving from right and left.
During this movement used oil on other side of piston will go out
through port 'A' and will return to the oil reservoir. When piston reaches
'left dead centre', flow through port 'B' stops and flow through port 'A'
starts. And cycle repeats which results into reciprocating motion of
piston.
o In DA cylinder spring is not required as in case we used in SA
cylinder, because reciprocating motion is done by pressure oil
coming in through 2 ports.
o In DA cylinder both strokes (right to left and left to right) are power
strokes and we can use this power to do useful mechanical work.
DOUBLE ACTING CYLINDER WITH SINGLE PISTON ROD
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7. Construction: As stated in its name, this hydraulic cylinder is having 2
piston rods of same diameter attached to the piston. The piston is
reciprocating in cylinder tube bore having high finish.
Working: When pressurised oil enters through port A, piston will move
towards right. When oil enters through port B, piston will move
towards left and used oil on left side of piston earlier stroke will return
to oil tank through port A. The cycle repeats in each stroke. In this type
of DA cylinder, we can obtain useful work at both ends of the cylinder.
This DA cylinder is used in controlling table movement in cylindrical
grinding machine and surface grinding machine.
DOUBLE ACTING CYLINDER WITH DOUBLE PISTON ROD
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8. Construction: As shown in the Fig. two cylinders are joined in 'series'.
There is a sealed partition between two cylinders. Two pistons are
fitted on one single piston rod. This arrangement is called 'tandem
array'. There are four ports A, B, C and D as shown.
Working: Pressurized oil is admitted at a time through ports (B) and
(D). Piston will move towards left with double force.
Similarly, pressurised oil is admitted at a time through ports (A) and
(C), piston will move towards right with double Force.
The main advantage of this DA cylinder is that we can obtain double
force with same size of cylinder.
TANDEM CYLINDER
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9. Construction: Fig. shows three Rams assembled in each other like
telescope (or Radio Antenna). This arrangement provides relatively
long stroke with good mechanical strength. There are two inlet ports
through which pressurised hydraulic oil enters. Port (R) is for raising
the cylinder or extending the cylinders while port (L) is for cylinder
lowering.
Working:
(1) Raising or Extending the cylinders: Hydraulic oil under pressure
will enter through port(R). Space 'X' will be filled by oil and Ram 1
will start raising upwards. When its raising stops, the oil now will
start entering through and will occupy space 'Y'. Due to this Ram
2will raise. When raising of Ram 2 stops, the oil will start entering
through and will occupy space 'Z', This will raise final Ram 3
upwards.
(2) Lowering the rams: When pressurised oil will enter through port
(L), then Ram 1 will come down. After its lowering Ram 2 will lower
and then Ram 3 will lower.
As shown in adjacent Fig. the dumper which is having movable bucket
carries heavy material like stone metal, stone boulders etc. The
unloading of bucket is operated on telescopic cylinder.
TELESCOPIC CYLINDER
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10. CYLINDER MOUNTINGS
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