The hydraulic pump is the heart of a hydraulic system. Its function is to convert mechanical energy into hydraulic energy by pushing the hydraulic fluid into the system.
The pump is an energy conversion element, which receives energy from the prime mover, generally an electric motor or engine, and imparts it to the fluid. Most of the hydraulic pumps receive fluid from the reservoir and pump it to the loaded actuator to perform work.
Different types of Hydraulic pumps are designed and manufactured over a wide range of construction capacities, to suit the particular requirement of the application. Various modifications and accessories are added to the basic pump design to enhance its performance by various manufacturers.
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Classification of Hydraulic Pumps
There are different types of pumps but are generally classified on the following basis.
Classification based on the principle of operation
- Hydrostatic type pumps (Positive Displacement)
- Hydrodynamic type pumps (Non-Positive displacement)
Classification based on the displacement
- Constant displacement pumps.
- Variable displacement pumps.
Classification based on construction
- Gear type pumps – External and Internal gear pump.
- Vane type pumps – Constant and Variable displacement vane pump.
- Piston type pumps – Radial and Axial piston pumps.
- Screw type pumps.
- Ball piston-type pumps.
Commonly used different types of hydraulic pumps are shown in fig.
|Types of Hydraulic Pumps|
Different Types of Hydraulic Pumps
There are 5 different types of Hydraulic Pumps.
- Gear Type Pump
- Vane Type Pump
- Piston Type Pump
- Screw Type Pump
- Ball Type Pump
These different types of Hydraulic Pumps are discussed below.
Gear Type Pumps
External Gear Pump
Gear pumps are positive displacement pumps. A partial vacuum is created as the internal gears go through their cycle, and oil is forced up into the pump due to atmospheric pressure on the oil surface. This oil is then carried to the delivery port by teeth and finally forced out to the actuator.
Advantages of External Gear Pump
- High speed/pressure
- Quiet operation
- Variety of build material options.
Disadvantages of External Gear Pump
- Bushing wear in liquid areas.
- Fixed end clearances.
Internal Gear Pump
An internal gear pump works on the same principle as that of an external gear pump but differs in construction. As the name implies it has one internal gear and another external gear.
|Internal Gear Pump|
Advantages of Internal Gear Pump
- Smooth and pulseless flow.
- Slightly more horsepower for size
Disadvantages of Internal Gear Pump
- Higher cost
- Limited size range
- Low to moderate pressure ratings
- Few sources of manufacture.
Gerotor type Pump
The gerotor pump is operated much like an internal gear pump, but it has a little difference in construction and operation. Gerotor pump comes under the category of gear pumps because the gerotor element has the gear like shape, but it doesn’t mesh like the gear.
|Gerotor type pump|
Vane Type Pump
Vane type pumps operate on the principle of increasing and diminishing volume. The oil from the suction port is confined into a chamber comprising sliding vanes and as the rotor proceeds the volume of this chamber goes on reducing resulting pressure in the fluid and in last the pressurized fluid is discharged into the delivery chamber.
Read also: Different types of Hydraulic Cylinders
Unbalanced type Vane Pump
An unbalanced type vane pump is the simplest version of vane-type pumps. It consists of a rotor in which vanes are held in a series of slots around the rotor. The rotor is offset within the housing and the vanes are constrained by the cam ring as they cross inlet and outlet ports.
|Unbalanced Type Vane Pump|
Balanced type Vane Pump
The pressure difference between the inlet and outlet ports creates a severe load on the vanes and a side load on the rotor shaft. To counterbalance this sideload the construction of the vane pump is little modified as shown in the figure.
Such construction is called a Balanced type vane pump.
|Balanced Type Vane Pump|
Variable Delivery Vane Pump
The construction of a vane pump is modified to make it variable displacement. The displacement from a vane pump depends on vane throw, vane across the sectional area, and the rotational speed.
|Variable Delivery Vane Pump|
Advantages of Vane Pump
- Handles low viscosity fluids at high pressure
- Dry run for short periods
- Develops good vacuum
Disadvantages of Vane Pump
- Unsuitable for high pressure
- Does not run high viscosity fluid.
Piston Type Pumps
The piston-type pumps operate on the same principle as that of a reciprocating pump. Piston-type hydraulic pumps have several pistons arranged such that some of them are sucking the fluid while others delivering it.
Piston type pumps are of the following types
- Radial Piston Pump
- Axial Piston Pump
Axial piston pumps are further divided into two types
- Swash Plate
- Bend axis
Radial Piston Pump
A radial piston pump has a fixed casing incorporating suction and delivery ports in it. Inside the fixed casing, there is a rotating piston block, and at the center, there is a fixed eccentric cam, whose center of rotation of the block is offset by an amount.
|Radial Piston Pump|
Swash Plate Type Axial Piston Pump
Swashplate type axial piston pump as shown in the diagram consists of a rotating cylinder barrel, which consists of a piston arranged on it axially. The piston ends are connected to an inclined swashplate.
|Swash Plate Axial Piston Pump|
The direction of the piston movement is decided by its peripheral position on the swashplate.
Bent Axis Type Piston Pump
Bent axis type piston pump consists of a cylinder barrel, which carries pistons arranged on it axially. The piston ends are connected to a flange by ball joints.
|Bent Axis Piston Pump|
The cylinder barrel is inclined at an angle alpha with the axis of rotation of the flange.
Screw Type Pump
Screw type pumps use screws to transmit fluid from suction to delivery port. The fluid is carried forward to the discharge by the screw, very much similar a nut moves along a screw. The helical grooves on the screws serve as the path for fluid from the suction chamber to the delivery chamber.
|Screw Type Pump|
As the screw rotates it draws oil from the suction chamber, enfolds it to the helical grooves. As the screw further rotates the fluid gets transferred along the screw and finally forced into the delivery chamber. Hence, oil is sucked continuously from four points and finally discharged into the delivery chamber.
Ball Type Pump
The ball piston pump is a very simple pump design. It has a rotor, which revolves around an internal stator. The rotor has twelve cylinders machined out of it, and each cylinder has a ball inside, which can slide in and out of the cylinder. The cylinder passes over the intake port for 180 degrees, then passes over the outlet port for 180 degrees.
|Ball Piston Pump|
The balls ride along two railed tracks, machined into the outer housing, the balls revolve around the pump in a perfect circle. Because the center point of the circle on which the balls revolve around is offset from the center point of the stator and the rotor, the balls, and the rotor have a relative motion to each other. This relative motion increases and decreases the volume of each cylinder, allowing the mechanism to draw in fluid during a one-half cycle and expel it during the other half cycle.
This pump has a major advantage of high efficiency due to lower mechanical losses. The manufacturing of this pump requires a high degree of precision and accuracy.