- Gear pumps have a disadvantage of small leakage due to gap between gear teeth and the pump housing. This limitation is overcome in vane pumps.
- The leakage is reduced by using spring or hydraulically loaded vanes placed in the slots of the driven rotor.
- Vane pumps are available in a number of vane configurations including sliding vane, flexible vane, swinging vane, rolling vane, and external vane etc.
- The operating range of these pumps varies from – 32 °C to 260 °C.
Working principle of Vane Pump :
- The schematic of the vane pump working principle is shown in figure. Vane pumps generate a pumping action by tracking of vanes along the casing wall.
- The rotor in a vane pump is connected to the prime mover through a shaft. The vanes are located on the slotted rotor.
- The rotor is eccentrically placed inside a cam ring as shown in the figure. The rotor is sealed into the cam by two side plates.
- When the prime mover rotates the rotor, the vanes are thrown outward due to centrifugal force. The vanes track along the ring.
- It provides a tight hydraulic seal to the fluid which is more at the higher rotation speed due to higher centrifugal force. This produces a suction cavity in the ring as the rotor rotates. It creates a vacuum at the inlet and therefore, the fluid is pushed into the pump through the inlet.
- The fluid is carried around to the outlet by the vanes whose retraction causes the fluid to be expelled.
- The capacity of the pump depends upon the eccentricity, expansion of vanes, and width of vanes and speed of the rotor. It can be noted that the fluid flow will not occur when the eccentricity is zero.
- These pumps can handle thin liquids (low viscosity) at relatively higher pressure.
- However, these pumps are not suitable for high-speed applications and for the high viscosity fluids or fluids carrying some abrasive particles.
- The maintenance cost is also higher due to many moving parts.
Vane Pumps types
There are two types of vane pumps:
1. Unbalanced vane pump: Unbalanced vane pumps are of two varieties:
- Unbalanced vane pump with fixed delivery.
- Unbalanced vane pump with pressure-compensated variable delivery.
2. Balanced vane pump.
Unbalanced Vane Pump with Fixed Delivery
A simplified form of unbalanced vane pump with fixed delivery and its operation is shown in Figs. The main components of the pump are the cam surface and the rotor. The rotor contains radial slots splined to drive shaft. The rotor rotates inside the cam ring. Each radial slot contains a vane, which is free to slide in or out of the slots due to centrifugal force. The vane is designed to mate with the surface of the cam ring as the rotor turns. The cam ring axis is offset to the drive shaft axis. When the rotor rotates, the centrifugal force pushes the vanes out against the surface of the cam ring. The vanes divide the space between the rotor and the cam ring into a series of small chambers. During the first half of the rotor rotation, the volume of these chambers increases, thereby causing a reduction of pressure.
This is the suction process, which causes the fluid to flow through the inlet port. During the second half of rotor rotation, the cam ring pushes the vanes back into the slots and the trapped volume is reduced. This positively ejects the trapped fluid through the outlet port. In this pump, all pump-action takes place in the chambers located on one side of the rotor and shaft, and so the pump is of an unbalanced design. The delivery rate of the pump depends on the eccentricity of the rotor with respect to the cam ring.
Read More :
- Screw Pump | Working, Design, Advantages and Disadvantages
- External Gear Pump | Design, Advantages and Disadvantages
- What is Positive Displacement Pumps | Types and Advantages
Balanced Vane Pump with Fixed Delivery
A balanced vane pump is a very versatile design that has found widespread use in both industrial and mobile applications. The basic design principle is shown in Fig. The rotor and vanes are contained within a double eccentric cam ring and there are two inlet segments and two outlet segments during each revolution. This double pumping action not only gives a compact design, but also leads to another important advantage: although pressure forces acting on the rotor in the outlet area are high, the forces at the two outlet areas are equal and opposite, completely canceling each other. As a result, there are no net loads on shaft bearings. Consequently, the life of this type of pump in many applications has been exceptionally good. Operating times of 24000 h or more in industrial applications are widespread. In more severe conditions encountered in mobile vehicles, 5000–10000 h of trouble-free operation is frequently achieved.
Balanced Vane Pump Diagram :
Advantages and disadvantages of Vane Pumps
The advantages of vane pumps are as follows:
1. Vane pumps are self-priming, robust, and supply constant delivery at a given speed.
2. They provide uniform discharge with negligible pulsations.
3. Their vanes are self-compensating for wear and vanes can be replaced easily.
4. These pumps do not require check valves.
5. They are light in weight and compact.
6. They can handle liquids containing vapors and gases.
7. Volumetric and overall efficiencies are high.
8. Discharge is less sensitive to changes in viscosity and pressure variations.
The disadvantages of vane pumps are as follows:
1. Relief valves are required to protect the pump in case of sudden closure of delivery.
2. They are not suitable for abrasive liquids.
3. They require good seals.
4. They require good filtration systems and foreign particles can severely damage the pump.
Advantages and disadvantages of balanced vane pumps
The advantages of balanced vane pumps are as follows:
1. The balanced pump eliminates the bearing side loads and therefore high operating pressure can be used.
2. The service life is high compared to the unbalanced type due to less wear and tear.
The disadvantages of balanced vane pumps are as follows:
1. They are fixed displacement pumps.
2. Design is more complicated.
3. The manufacturing cost is high compared to the unbalanced type.
Application of Vane Pump :
These pumps have various applications for the pumping of the following fluids:
- Aerosol and Propellants
- Aviation Service – Fuel Transfer, Deicing
- Auto Industry – Fuels, Lubes, Refrigeration Coolants
- Bulk Transfer of LPG and NH3
- LPG Cylinder Filling
- Refrigeration – Freons, Ammonia
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