A vane pump is a positive displacement pump that is used to increase the pressure of the flowing fluid using the vanes which are mounted to a rotor.
This pump can be used to flow the fluid from one point to another at high pressure.
The vanes in the vane pump can have the variable-length or can be tensioned to maintain the contact of the vanes with the wall of the pump as the vanes rotate.
The vane pump was invented by Charles C. Barnes in 1874.
The modern vane pumps have area contact between the rotor and the stator rather than having a line contact.
Vane pumps are commonly used in automobiles, power steering of vehicles, and are also used in air conditioners.
The vane pump is not good for a highly viscous fluid. Vane pumps can handle moderate viscous fluid and they are excellent for handling low viscous fluids like L.P gas, ammonia, solvents, alcohol etc.
It is also used to convert high-pressure gas to low-pressure gas.
Components of Vane Pump:
The casing is the outer covering of the vane pump. All other components of the vane pump are present inside this casing.
There are two ports in the casing:
i) Inlet port:
The fluid enters the pump through this inlet port.
ii) Outlet Port:
High pressure fluid leaves the pump through outlet port.
There is a shaft inside the vane pump which is connected to a prime mover.
A rotor is mounted on the shaft and it rotates using the power of the prime mover.
The rotor of the vane pump has slots that are present at an equal distances all around the rotor.
This rotor has various radial slots in it.
4) Sliding Vanes:
Sliding Vanes are present in the slots of the rotor. The slidng vanes move inside the slots of the rotor freely. The sliding vanes are of rectangular shape and are attached with the rotor using a spring.
5) Cam Ring:
Cam Ring is present at the inner wall of the casing.
Working Of Vane Pump:
- At first, power is provided to the shaft of the pump using an electric motor.
- After providing power, the shaft starts rotating and the rotor which is mounted on the shaft also starts rotating.
- When the rotor rotates, the sliding vanes present at the slots of the rotor experience a centrifugal force that is directed radially outward.
- Due to the centrifugal force on the sliding vanes, the vanes move outward and the spring which connects the rotor and vanes get extended.
- Then the springs extend and sliding vanes establish contact with the cam-ring and this contact is established as long as the rotor rotates.
- When the vanes reach a position where the distance between the rotor shaft and casing is less, the spring of the vane compresses to maintain contact with the cam-ring. At this position, the area between the two adjacent vanes and the casing is also less i.e the pocket size is less.
- Similarly, when the vanes reach a position where the distance between the rotor shaft and the casing is more, the spring of the vane expands to maintain contact with the cam-ring. At this position, the area between the two adjacent vanes and the casing is also more.
- When the rotor rotates continuously, after some time a suction is created in the inlet port due to which fluid gets sucked into the inlet port.
- The fluid which is sucked through the inlet gets stuck between the two adjacent vanes and as the vanes are always in contact with the cam-ring, the stuck fluid rotates along with the two adjacent vanes.
- While moving from the inlet port to the outlet port, the fluid experiences a centrifugal force which increases the pressure of the fluid, and this high-pressure fluid is delivered to the required area through the outlet port.
- Near the inlet of the vane pump, the space between two adjacent vanes increases due to the increased distance between the shaft and casing. As the space increases between two adjacent vanes, a vacuum is created near the vane pump’s inlet. Due to the vacuum created, the suction starts, and the fluid is drawn in from the inlet of the pump.
- After that, as the rotor continues to rotate the compression of the entrapped fluid starts due to a decrease in the space between adjacent vanes i.e the pocket size decreases. As the pocket size decreases, the volume of the fluid decreases, and the entapped fluid gets compressed and the pressure of the fluid increases. After that, the high-pressure fluid is discharged from the outlet of the vane pump.
Types Of Vane Pumps:
There are mainly three types of vane pumps:
1) Unbalanced Vane Pump
2) Balanced Vane Pump
3) Variable Displacement Vane Pump
1) Unbalanced Vane Pump:
>> The unbalanced vane pump is the regular vane pump that you have studied in this article.
>> It consists of a cylindrical rotor which is mounted at an offset inside a circular casing. It means the center of the cylindrical rotor and the center of the casing do not coincide. The Center of the casing and the center of the rotor are at some distance.
>> No leakage occurs between the vane tips and the casing.
>> A side thrust is created on the rotor shaft due to differences in pressure between the inlet and the outlet ports. Due to the side thrust on the rotor shaft, the bearing life reduces. Due to differences in pressure in the inlet and the outlet port, this vane pump is called an unbalanced vane pump.
>> In a balanced vane pump, there is no side thrust on the rotor shaft.
2) Balanced Vane Pump:
>> In a balanced vane pump, the casing is elliptical in shape. The center of the rotor and the elliptical casing is the same and no offset is used.
>> For balancing, two inlets, and two outlets are provided due to which no pressure difference is created between the inlets and the outlets.
>> Two inlets are present on the opposite side of each other and the two outlets are present on the opposite side of each other.
>> Due to this type of arrangement of inlets and outlets, the equal and opposite thrust gets balanced and hence no side thrust is experienced by the rotor shaft.
>> The balanced pump gives better service and longer life.
>> The pocket-size between two vanes increases when moving from outlet to inlet and pocket-size decreases when moving from inlet to outlet. Hence there is suction in the inlet ports and delivery at the outlet ports.
3) Variable Displacement Vane Pump:
>> In a variable displacement vane pump, the pocket-size can be varied.
>> Due to varying pocket sizes, the discharge from the outlet varies.
>> In this variable displacement vane pump, the vane is not in direct contact with the casing.
>> In between the casing and the vane a ring is provided and this ring is called a reaction ring.
>> On one side the reaction ring is connected with the adjusting screw and on the other side, it is connected with a spring.
>> The adjusting screw is used to vary the pocket size of this pump.
>> By turning the adjusting screw, the reaction ring can be moved upward or downward.
>> By moving the reaction ring upward or downward, the offset between the reaction ring center and the rotor center.
>> As the offset changes, the pocket-size also changes and hence the discharge from the pump varies.
Advantages Of Vane Pump:
1) It can handle low viscosity fluids at high pressures.
2) It can dry runs for short periods.
3) This pump develops a good vacuum.
Disadvantages Of Vane Pump:
1) It has a complex design.
2) It is unsuitable for high viscosity fluid at high pressure.