Dry vane pumps or oil-less vane pumps are like most other pumps but feature some advantages over other standard vacuum pumps. Vane pumps are positive displacement pumps that contain many sliding vanes rotating within a cavity. The output of the pump should be constant irrespective of the input provided. This is the sign of a good pump.
Rotary metals suffer from very little wear as there is very negligible metal to metal contact. This affects their performance which shows a very efficient operating duration which is far higher compared to other vane pumps. Dry vane pumps make use of little to no lubrication at all. Non-requirement of lubrication reduces the overall cost of operation. The lubrication is provided by vanes made of graphite material which by itself is a very good lubricant.
The Working Process
The rotor contains radial slots which house the vanes and the entire setup containing the rotor and the vanes rotate inside a cam ring. The slots are designed in such a way that they always remain in contact with the inner surface of the cam ring. As the rotor rotates, the vanes are forced to stick out, pushing towards the cam ring due to centrifugal force.
One half of the cycle has an increasing volume between the rotor and the cam ring whereas in the other half cycle the volume will be decreasing. The working fluid is sucked in between the vanes as the volume begins to rise. Pressure begins to rise as the volume begins to reduce during the next half-cycle. This stage is repeated until the desired pressure is achieved. At the end of this half-cycle, the working fluid is ejected.
Benefits of Dry Vane Pumps
- As mentioned earlier dry vane pumps are completely oil-free.
- Despite lacking any proper lubricating medium, dry vane pumps are quiet and are not heated up while under operation. This is attributed to the excellent self-lubricating property of graphite which is used in the vanes.
- These pumps have a long vane life.
- There is no chance of lubricant leakage and are thus environment friendly.
- Positive displacement pumps have a major disadvantage. They continue to pump the fluid even when the fluid has no place to go which results in overpressure at the exit compared to the inlet. This, in turn, implies there will be a backflow of fluid. However dry vane pumps come with fluid regulators that avoid overpressure and backflow.
- Dry vane pumps also require little to no maintenance as they do not need lubricant.
- They operate over a wide temperature range.
Disadvantages of Dry Vane Pumps
- Dry vane pumps may come with a boatload of features and advantages, but they are not suitable for every job. Dry vane pumps are not advisable for applications involving vacuum levels exceeding 28 HGV. They can also be used where the inlet flow is very large.
- The efficiency of dry vane pumps is lower than 30%, whereas those of very high specs may rake in around 50%.
- Dry vane pumps are not suitable for the oxygen-rich working atmosphere as there is a very high possibility of metal corrosion.
- They cannot be used when highly corrosive gases, explosive gases are used as working fluid.
Dry vane pumps are ideal for vacuum packaging and vacuum forming. The maximum pressure that can be achieved by these pumps is dependent upon the working fluid and it is considerably lower compared to gear pumps. So, from here we can conclude that vane pumps are much better than another kind of pumps.