The types of rotary pumps are
- Gear pump
- Vane pump
- Lobe pump
In a gear pump, two gears are placed inside a hollow casing in such a way that they rotate in opposite direction. One of these two gears is given rotary motion. The other gear will also rotate meshing with the first one. The shaft on the driving gear will be extending outside to get rotation from a prime mover. A little gap is left between the gears and the casing.
Method of working – The inlet of the pump is immersed in the reservoir. The prime mover actuates the driving gear. This movement makes the other gear also to rotate. As these gears rotate, the liquid is trapped between their teeth and the casing. The liquid is pumped out through the outlet of the pump.
Uses – Lubricating oil and liquids with high viscosity are pumped by pumps fitted with spur gears. Pumps with helical gears are useful in pumping water and chemicals. Gear pumps can handle pressures upto 140 k.g/cm2. The output can be 450 litres per min.
Construction – Vane pumps are equipped with a rotor. Radial slots are present on the rotor. Vanes are attached to these slots and are designed to slide inside them. Rotor is placed inside the casing. The casing and the rotor are placed eccentric. When the rotor is made to rotate, vanes come out of the slots due to centrifugal force. Vanes rotate by touching the inner walls of the casing. In some pumps, vanes are attached to the slots by means of springs to in- crease the pressure.
Method of working – The rotor is rotated by a prime mover. The liquid is trapped in between the vanes. The design of the pump is such that the volume of the incoming liquid is increrasing and the volume of the out going liquid is decreasing. So the liquid from the outlet is pumped with increased pressure. Care is taken that the outlet volume of the liquid does not go back to the inlet.
A single layer vane pump can handle pressures from 17.5 to 70 k.g/cm2 and a two layer pump can handle upto 150 k.g/cm2 of pressure.