Explains the types of Pumps

1. Hydraulic Pumps

2. Basic hydraulic system with linear hydraulic actuator (cylinder).

3. Basic hydraulic system with rotary hydraulic actuator (motor)

7. A pump, which is the heart of a hydraulic system, converts mechanical
energy into hydraulic energy. The mechanical energy is delivered to the
pump via a prime mover such as an electric motor. Pump generates the
force necessary to move the load.
Due to mechanical action, the pump creates a partial vacuum at its inlet.
This permits atmospheric pressure to force the fluid through the inlet line
and into the pump. The pump then pushes the fluid into the hydraulic
system.

8. • The hydraulic pump in a hydraulic system converts mechanical
energy in to hydraulic energy (pressure energy).
• The pump draws in the hydraulic fluid and drives it out in to a
system of lines. The resistances encountered by the flowing
hydraulic fluid cause a pressure to build up in the hydraulic system.
• Thus the fluid pressure in a hydraulic system is not predetermined by
the pump. It builds up in accordance with the resistances – in
extreme cases until a component is damaged. In practice it is
prevented by installing a pressure relief valve directly after the pump
or in the pump housing at which the max operating pressure
recommended for the pump is set.

10. 1. Dynamic (nonpositive displacement) pumps. This type is
generally used for low-pressure, high-volume flow applications.
Because they are not capable of withstanding high pressures,
they are of little use in the fluid power field.
2. Positive displacement pumps. This type is universally used
for fluid power systems. As the name implies, a positive
displacement pump ejects a fixed amount of fluid into the
hydraulic system per revolution of pump shaft rotation. Such a
pump is capable of overcoming the pressure resulting from the
mechanical loads on the system as well as the resistance to
flow due to friction.

11. Hydraulic Pump types
• PUMPS
NON POSITIVE DISPLACEMENT PUMPS POSITIVE DISPLACEMENT PUMPS
CENTRIFUGAL
PUMP
PROPELLER
PUMP
VANE
PUMP
GEAR
PUMP
GEROTOR
PUMP
LOBE
PUMP
SCREW
PUMP
RECIPROCATING
PUMP
RADIAL
PISTON
PUMP
AXIAL
PISTON
PUMP

12. Non-positive pumps
• They are used for low-pressure, high-volume flow applications.
• Normally their maximum pressure capacity is limited to 17-20
bar.
Positive pumps (Gear, vane, piston pumps)
• High pressure capability (up to 700 bar or higher)
• Small compact size
• High volumetric efficiency
• Small changes in efficiency
• Great flexibility of performance
Hydraulic Pump types

13. It should be understood that pumps do not pump pressure. Instead
they produce fluid flow. The resistance to this flow, produced by the
hydraulic system, is what determines the pressure.
For example, if a positive displacement pump has its discharge
line open to the atmosphere, there will be flow, but there will be no
discharge pressure above atmospheric because there is
essentially no resistance to flow. However, if the discharge line is
blocked, then we have theoretically infinite resistance to flow.
Hence, there is no place for the fluid to go. The pressure will
therefore rise until some component breaks unless pressure relief
is provided. This is the reason a pressure relief valve is needed
when a positive displacement pump is used.

14. Positive displacement pumps have the following advantages over
nonpositive displacement pumps:
a. High-pressure capability (up to 830 bar)
b. Small, compact size
c. High volumetric efficiency
d. Small changes in efficiency throughout the design pressure range
e. Great flexibility of performance (can operate over a wide range of
pressure requirements and speed ranges)

15. PUMPING THEORY
Pumps operate on the principle whereby a partial
vacuum is created at the pump inlet due to the internal
operation of the pump. This allows atmospheric
pressure to push the fluid out of the oil tank (reservoir)
and into the pump intake. The pump then mechanically
pushes the fluid out the discharge line.

16. Displacement of pump
The flow capacity of a pump can be expressed as displacement per
revolution or output in (LPM) (L/min). Displacement is the volume of liquid
transferred in one revolution. It is expressed in cubic inches per revolutions.
In practice, the pump is rated in terms of how much fluid is supplied per unit
of time, and expressed in terms of: litres per minutes (LPM) (L/min).
Pumping theory:
Due to partial
vacuum oil is
rushed towards
the pump.

22. PUMP CLASSIFICATION
Dynamic Pumps

24. The two most common types of dynamic pumps are the centrifugal
(impeller) and axial (propeller) pumps shown in the above slide.
Although these pumps provide smooth continuous flow, their flow
output is reduced as circuit resistance is increased and thus are
rarely used in fluid power systems.

25. construction features of a centrifugal pump
The fluid enters at the center of the impeller and is picked up by the
rotating impeller. As the fluid rotates with the impeller, the centrifugal
force causes the fluid to move radially outward. This causes the
fluid to flow through the outlet discharge port of the housing.

26. Although dynamic pumps provide smooth continuous flow, their output flow rate is
reduced as resistance to flow is increased.
pump pressure is plotted versus pump flow reveals that the maximum pressure is
called the shutoff pressure ( pressure head )because an external circuit valve is
closed, which shuts off the flow. As the external resistance decreases due to the
valve being opened, the flow increases at the expense of reduced pressure.

28. Positive Displacement Pumps
Positive Displacement Pumps:
This type of pump ejects a fixed quantity of fluid per revolution of the pump shaft.
As a result, pump output flow, neglecting changes in the small internal leakage,
is constant and not dependent on system pressure. This makes them particularly
well suited for fluid power systems. However, positive displacement pumps must
be protected against overpressure if the resistance to flow becomes very large.

29. Positive displacement pumps can be classified by the type of
motion of internal elements.

30. GEAR PUMPS
External Gear Pump

32. EXTERNAL GEAR PUMP

33. Gear Pump
driven gear
idler gear

34. WORKING PRINCIPLE
• The pump consists of drive gear and a driven gear and closed in
closely fitted housing.
• The gears rotate in opposite direction and mesh at a point in
housing between inlet and outlet ports as the teeth of gear
separate, fluid is drawn into the inlet chamber, due to partial
vacuum the fluid is trapped between the gear teeth and housing
and carried through two separate paths around the outlet
chamber.
• As the teeth re-mesh, fluid is forced through the outlet port. Close
fit of the gear teeth within the housing is required to provide a seal
between inlet and outlet ports, minimizing internal leakage.

35. Gear Pumps
•Work well at 100 bar and below
•Work with a minimum of moving parts
•Less expensive to manufacture than piston type
pumps

36. The operation of an external gear pump, which develops flow by
carrying fluid between the teeth of two meshing gears. One of the
gears is connected to a drive shaft connected to the prime mover.
The second gear is driven as it meshes with the driver gear. Oil
chambers are formed between the gear teeth, the pump housing, and
the side wear plates.

38. The volumetric displacement can be represented by
The theoretical flow rate is determined next:
QT ( m3/min) = VD (m3/ rev) * N (rev/min)

40. The actual flow rate QA is less than the theoretical flow
rate QT, which is based on volumetric displacement and
pump speed. This internal leakage, called pump slippage,
is identified by the term volumetric efficiency, ηv, which
equals about 90% for positive displacement pumps,
operating at design pressure: