2. PUMP
Pump is the heart of the system.
A hydraulic pump takes oil from the tank and delivers it to
the rest of the hydraulic circuit. In doing so it raises the oil
pressure to the required level.
Fig. a) Operation of Pump Fig. b) Pump symbol,
arrow shows the
direction of flow
3. CAVITATION
When the suction pressure drops below the vapour
pressure, the liquid oil starts changing to vapour state.
They began to appear as bubbles.
When these bubble collapse, vacuum is created.
Due to these liquid from the surrounding region rushes to
the spot and create a momentarily high pressure of very
high order (about 105 bar).
This results in damage of the metallic parts of pump.
Cavitation occurs on the control edges of the hydraulic
device.
High increase in temperature occurs.
4. BASIC PUMP
The basic operating principle that moves fluid through
a pump is similar in all pumps,
Enlarging the volume of a chamber allows fluid to
enter the pump.
Reducing the chamber volume moves fluid to the
system
Inlet and discharge valves or ports control fluid
movement through the pump.
8. NON-POSITIVE
DISPLACEMENT PUMP
Non positive displacement pumps – high clearance between
rotating and stationary parts.
Characterized by a high slip that increases as the back
pressure increases, but if the opposing pressure is high then
the kinetic energy of the liquid becomes insufficient to
overcome the pressure and the liquid cannot move. Due to
more clearance gap between impeller and casing, the liquid
keeps on rotating inside casing.
They do not develop a high pressure but move a large
volume of fluid at low pressure.
The displacement between the inlet and outlet is not positive,
therefore the volume of the fluid delivered by the pump
depends on the speed at which pump is operated and the
resistance at discharge side.
In short, the discharge does not remain constant.
10. ADVANTAGES &
DISADVANTAGES
ADVANTAGE
a. Non-displacement
pumps have a fewer
moving parts
b. Initial and
maintenance cost is
low
c. They give smooth
continuous flow
d. They are suitable for
handling all types of
flow especially slurries
e. Their operation is
simple and reliable.
DISADVANTAGE
a. Non-displacement
pumps are not self
priming and hence
they must be
positioned below the
fluid level
b. Discharge is a
function of output
resistance
c. Low volumetric
efficiency
11. POSITIVE
DISPLACEMENT PUMP
Positive displacement pumps – have a very little slips, are
self priming and pump against a very high pressure but
their volumetric capacity is low.
These types of pump eject a fixed amount of fluid into the
hydraulic system per revolution of the pump shaft.
Such pumps are capable of overcoming the pressure
resulting from mechanical loads on the system as well as
the resistance of flow due to friction
These are always protected by relief valves to prevent
damage to the pump or system.
A majority of fluid power pumps fall in this category, such
as Gear, Piston and Vane pumps.
12. ADVANTAGES OF PDP
OVER NPDP
They can operate at very high pressure of up to 800 bar
( used for lifting oils from very deep oil wells)
They can achieve a high volumetric efficiency of 98 %
They are highly efficient and almost constant throughout
the designed pressure range.
They are a compact unit having a high power to weight
ratio
They can obtain a smooth and precise controlled motion.
By proper application and control, they produce only an
amount of flow required to move the load at the desired
velocity
They have a great flexibility of performance. They can be
made to operate over a wide range of pressures and
speeds.
13. ROTARY PUMPS
Rotary pumps are positive displacement pumps
They have two or more rotating components.
The discharge of rotary pumps remains almost same
irrespective of pressure. They can give discharge even at a
high pressure. They are limited to pressure below 140 bar.
The discharge of rotary pumps is smooth, continuous and
not pulsating. A very less vibration and noise is observed.
They are compact with less number of moving component
and less sensitive to contaminations.
14. CLASSIFICATION-ROTARY PUMPS
I. GEAR PUMPS
I. External gear pumps
II. Internal gear pumps
III. Lobe pump
IV. Ge-rotor pump
V. Screw pump
II. VANE PUMPS
I. Unbalanced vane pump
II. Balanced vane pump
III. PISTON PUMPS
I. Axial piston pump
I. Straight axis piston pump
II. Bent axis piston pump
II. Radial piston pump
I. Stationary cylinder type
II. Rotating cylinder type
16. EXTERNAL GEAR PUMPS
It consist of pump housing in which a pair of precisely
machined meshing gears run with minimal radial and axial
clearance.
One of the gears, called as Driver is driven by a prime mover.
The Driver drives another gear called a Follower.
As the teeth of the two gears separate, the fluid from the pump
inlet gets trapped between the rotating gear cavities and pump
housing.
The trapped fluid is then carried around the periphery of the
pump casing and delivered to the outlet port.
The teeth of the precisely meshed gears provide almost a
perfect seal between a pump inlet and pump outlet.
The inlet is at the point of separation and the outlet is at the point
of mesh.
17. EXTERNAL GEAR PUMPS
ADVANTAGE
1. They are self-priming.
2. They give constant
delivery for a given
speed
3. They are compact
and light in weight
4. Volumetric efficiency
is high
DISADVANTAGE
1. The liquid to be
pumped must be
clean, otherwise it
will damage the
pump.
2. Variable speed drives
are required to
change the drive.
3. If they run dry, parts
can be damaged
because the fluid to
be pumped is used
as lubricant.
20. LOBE PUMP
The lobe pump is a close relative of the external gear pump.
― Two three-lobed, gear shaped units are often used to form
the pumping element
― Output flow is larger than a gear pump of comparable
physical size because of pumping chamber geometry
― Lower pressure rating than the gear pumps, but higher
discharge is achieved
― Tend to have a pulsating output flow.
22. INTERNAL GEAR PUMPS
— Another form of gear pump is Internal Gear pump.
— They consist of two gears: An External and an Internal Gear
— The crescent placed in between acts as a seal between the
suction and discharge.
— When the pump operates, the external gear drives the
internal gear and both rotate in same direction.
— After the un-meshing of the gears at the inlet, the fluid fills
the cavities formed by rotating teeth and crescent.
— Both the gears transport the fluid through the pump. The
crescent seals the low pressure pump inlet from the high
pressure pump outlet.
25. GE-ROTOR PUMP
The ge-rotor is a common internal gear pump
The inner gear rotor is called as the gerotor element.
The element is driven by prime mover and during the
operation drives outer gear rotor around as they mesh
together.
The gerotor has one tooth less than the outer idler gear
Each tooth of gerotor is always in sliding contact with
surface of outer element, the teeth of two elements engage
at just one place to seal pumping chambers
The pocket of increasing size are suction pockets and
those of the discharge side are of discharge.
26. SCREW PUMP
Screw pump has pumping elements that consist of one,
two or three rotating screws.
As the screw rotates, fluid is trapped and carried along to
the discharge of the pump
The design screw allows them to operate at a very low
noise level.
A single screw version is called as “Progressive Cavity
Pumping”
28. VANE PUMP
Vane pumps are positive-displacement, fixed or variable
delivery units.
Design is commonly used in Industrial applications.
Vane pumps consist of slotted rotor, fitted with moveable
vanes, that rotates within a cam ring in the pump housing
- Rotor is off centre in the ring, which creates pumping
chambers that vary in volume as the pump rotates
- As chamber volume increases, pressure decreases,
bringing fluid into the pump
- As volume decreases, fluid is forced out into the system.
30. VANE PUMP
Vane pump may be pressure unbalanced or pressure
balanced
- Unbalanced has only one inlet and one discharge which
places a side load on the shaft
- Balanced has two inlets and two discharge opposite each
other, creating a pressure balance and therefore no load
on the shaft
32. PISTON PUMP
A basic piston consist of a housing that supports a pumping
mechanism and a motion converting mechanism
- Pumping mechanism is a block containing cylinders fitted
with pistons and valves
- Motion converter changes rotary to reciprocating motion
via cams, eccentric ring, swash plate or bent axis design.
- Rotating the pump shaft can cause piston movement that
pumps the fluid.
33. FUNCTION OF SWASH
PLATE
Swash plate is used to change the discharge of the pump
By changing the angle of swash plate, we can change the
stroke length and hence the discharge.
When swash plate is perpendicular to the pump axis, the
discharge is zero
Discharge increases with the increase in swash plate
angle from this perpendicular to pump axis.
35. BENT AXIS PISTON PUMP
It consist of cylinder block with axial bores
Pistons are inserted inside these bores. The other end of
the plate are connected to the shoe plate with shoe joints.
In bent axis piston pump, the shoe plate is fixed to a
flange; the flange is keyed to drive shaft.
When the shaft rotates, it causes the cylinder block to
rotate, the shoe plate will also rotate with it, causing the
piston in the bores to reciprocate
Half rotation of the cylinder block causes suction of the oil
into the bore and the next rotation causes the discharge.
37. FACTORS AFFECTING
THE SELECTION OF TYPE
OF PUMP
1. Maximum operating pressure
2. Maximum delivery
3. Type of control
4. Pump drive speed
5. Type of fluid
6. Pump contamination tolerance
7. Pump noise
8. Size and weight of pump
9. Pump efficiency
10. Availability and interchangeability
11. Maintenance and spares
12. cost
