Hydraulic Cylinders and Their Applications
Lecture
5
Cylinders
Cylinders
are
linear actuators whose
output
force or motion
is
in
a
straight
line.
Their function
is to
convert
hydraulic power into linear
mechanical power. Hydraulic cylinders extend and retract
to
perform a
complete cycle of operation.
Their
work applications
may
include pulling, pushing,
and
pressing.
The
type
of
cylinder to
be
used
along
with
its design
is based
on
a specific
application.
The
simplest of linear actuators
is
a
ram
which
is
shown
in
Figure 1.
It
has
only
one
fluid
chamber and exerts force
in
one
direction
only.
Rams
are
widely
used
in
applications
where
stability
is
needed on
heavy loads.
Ram-type cylinders
are
practical
for
long strokes and
are
used
on
jacks, elevators and automobile
hoists.
Figure
1:
Hydraulic
ram
Hydraulic
cylinders
are
further classified
as:
•
Single
acting
cylinders
and
•
Double acting
cylinders
Single acting
cylinder
Single
acting cylinders
are
pressurized at
one
end only while
the opposite
end
is vented to the
atmosphere or
tank.
They
are
usually
designed
in
such
a way that a
device
such
as
an
internal spring retracts
them. Figure
2
is
an
illustration of
the
simplest
form
of a
single
acting
hydraulic
cylinder along with its symbolic
representation.
23
A
single
acting hydraulic cylinder
consists
of
a piston inside a cylindrical
housing
called a
barrel.
Attached
to one
end
of
the
piston
is
a rod, which
extends
outside
one end
of
the
cylinder
(rod
end). At
the
other end
(blank
end) is
a port for
the
entrance and exit of
oil.
Figure
2:
Single acting hydraulic
cylinder
Double
acting
cylinder
Double
acting cylinders
are the
most commonly
used
cylinders
in
hydraulic
applications.
Here
pressure can
be
applied
to
either
port giving
power
in
both directions. Figure 3 shows
the
typical construction of a
double
acting cylinder.
The
cylinder consists of
five basic
parts:
two
end
Blind
end
Piston
24
D
ra
i
n
caps (a
base
cap
and
a bearing cap) with
port
connections, a cylinder
barrel,
a piston and
the rod
itself.
This
basic construction
provides
for
simple manufacture
as
the
end caps and
pistons
remain
the
same
for
different lengths of
the
same
diameter cylinder. The end
caps
can
be
secured to the
barrel
by
welding, through tie rods or
by
threaded
connections.
25
Figure
3:
Construction
of
a double acting
cylinder
A
hydraulic
cylinder
is used to
compress a
car
body down
to
a
bale
size in
10
s.
The
operation requires a
10
ft
stroke
(S)
and
a force (Pbad) of 8000
lb.
If
a 1000
psi
pressure
(P)
pump is
selected,
find
(a)
The
required piston
area
(b)
The
necessary pump
flow
rate
(c)
The
hydraulic horsepower delivered
by the
cylinder
Solution:
Here
F
load
is
the
force
required
to
crush
the
car
for
which
the
pump
used
can deliver a pressure of 1000
psi.
So, to
get
the
area
of
the
piston
required
to
take
this
load,
(a)
Force = P
xA
so
P=
F
load
/A=
8000/1000
= 8
sq.in.
(b)
The
volumetric displacement of
the
cylinder
equals
the
fluid volume
swept
by the
cylinder
during its
stroke length
(5)
while
the required
pump
flow
rate equals the volumetric
displacement divided
by
the
time
required for
the
stroke.
So,
G(ftVs) =
(AxS)/t=
((8/144)
X10)
/
10
= 0.056
ft
3
/s
1 ft
3
/s =
448
gpm
So
26
27
=
448x0.056
= 25.1
gpm
In order
to
calculate
the power
delivered
we
will use the
equation
H
p
=[P(psi)xQ(gpm)]/1714
This
has been
derived
by
using the
conversion factors,
keeping in
view
the
basic
Power-energy equation which
is
Power
=Energy/Time
So
Hp
=
(1000x25.1)/1714
=
14.6hp
This
is the
theoretical horsepower delivered
by
the
cylinder assuming its
efficiency
to
be
100%.
Then,
to calculate
the
actual
hp, this
should
be
multiplied by
the
efficiency
specified
by
the
manufacturer.
Cylinders are linear actuators converting hydraulic power into mechanical power for pulling, pushing, and pressing tasks. They can be single-acting or double-acting, with specific designs for different applications. Ram-type cylinders offer stability for heavy loads, and double-acting cylinders are versatile for applications requiring power in both directions. Learn about the construction, components, and calculations involved in hydraulic cylinders' operation and use.
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Presentation Transcript
Lecture5 Cylinders Cylinders are linear actuators whose output force or motion is in a straight line. Their function is to convert hydraulic power into linear mechanical power. Hydraulic cylinders extend and retract to perform a completecycle of operation. Their work applications may include pulling, pushing, and pressing. The type of cylinder to be used along with its design is based on a specific application. The simplest of linear actuators is a ram which is shown in Figure 1. It has only one fluid chamber and exerts force in one direction only. Rams are widely used in applications where stability is needed on heavy loads. Ram-type cylinders are practical for long strokes and are used on jacks, elevatorsand automobilehoists. Figure 1: Hydraulicram Hydraulic cylinders are further classifiedas: Single acting cylindersand Double acting cylinders Single acting cylinder Single acting cylinders are pressurized at one end only while the opposite end is vented to the atmosphere or tank. They are usually designed in such a way that a device such as an internal spring retracts them. Figure 2 is an illustration of the simplest form of a single acting hydraulic cylinder along with its symbolic representation. 23
A single acting hydraulic cylinder consists of a piston inside a cylindrical housing called a barrel. Attached to one end of the piston is a rod, which extends outside one end of the cylinder (rod end). At the other end (blank end) is a port for the entrance and exit of oil. Blindend Piston Drain Figure 2: Single acting hydraulic cylinder Double acting cylinder Double acting cylinders are the most commonly used cylinders in hydraulic applications. Here pressure can be applied to either port giving power in both directions. Figure 3 shows the typical construction of a double acting cylinder. The cylinder consistsoffive basicparts: two end 24
caps (a base cap and a bearing cap) with port connections, a cylinder barrel, a piston and the rod itself. This basic construction provides for simple manufacture as the end caps and pistons remain the same for different lengths of the same diameter cylinder. The end caps can be secured to the barrel by welding, through tie rods or by threaded connections. 25
Figure 3: Construction of a double actingcylinder A hydraulic cylinder is used to compress a car body down to a bale size in 10 s. The operation requires a 10 ft stroke (S) and a force (Pbad) of 8000 lb. If a 1000 psi pressure (P) pump is selected, find (a) The required piston area (b) The necessary pump flow rate (c) The hydraulic horsepower delivered by the cylinder Solution: Here Fload is the force required to crush the car for which the pump used can deliver a pressure of 1000 psi. So, to get the area of the piston required to take this load, (a)Force = PxA so P= Fload /A= 8000/1000= 8sq.in. (b)The volumetric displacement of the cylinder equals the fluid volume swept by the cylinder during its stroke length (5) while the required pump flow rate equals the volumetric displacement divided by the time required forthe stroke. So, G(ftVs) = (AxS)/t= ((8/144) X10)/10 = 0.056 ft3/s 1 ft3/s = 448gpm So 26
= 448x0.056 = 25.1gpm In order to calculate the power delivered we will use the equation Hp=[P(psi)xQ(gpm)]/1714 This has been derived by using the conversion factors, keeping in view the basic Power-energy equation which is Power =Energy/Time So Hp = (1000x25.1)/1714 = 14.6hp This is the theoretical horsepower delivered by the cylinder assuming its efficiency to be 100%. Then, to calculate the actual hp, this should be multiplied by the efficiencyspecified by the manufacturer. 27
