Rotary pumps are a common pump type that is based on the principle of rotating parts that aid in trapping water or any fluid at the inlet and then channelize it, through the vacuum created into the port meant for discharge. These pumps are a kind of positive displacement pumping units. They are preferred as they automatically remove air from the pipe lines, hence eliminating the need to manually remove the air. Rotary pumps are highly efficient and are suited to operate at a steady, but relatively slow speed because high speed causes erosion of the rotating parts by the fluids that interfere with the efficiency and durability of the pump. Basically, there are three types of such pumps, which are discussed below.
1. Gear Pumps
The most basic type of rotary pumps, gear pumps operate on the movement of two gears that are placed beside each other such that the teeth of both are enmeshed. The gears move in opposing directions of each other, hence giving rise to a current that helps to trap fluid between the places where the teeth are, and the outer covering of the gears. The fluid is ultimately released on the discharge vent of the pump.
Generally there are two categories of gear pumps - the external and internal gear pump. The former is known as a gear pump commonly and the principle described in the previous lines govern them. Here the gaps between the teeth of the gear are responsible for the movement of the fluid from the inlet to the discharge outlet. The gears stay in place with the support of bearings present on both sides of the gears. The internal pump has two gears that un-mesh at the side of the suction unit and creates gaps which make the air pressure push in the fluid. These gaps make the fluid move to the discharge side and the rotating gears then re-mesh for discharging the fluid.
2. Screw Pumps
Employed mostly in irrigational departments, the screw pump uses the traditional principle of the Archimedean screw. These are a kind of rotary pump that have one to three screws that help in moving viscous fluids along the axis in the set up. The viscosity can be either high or low. The screws are placed such that they are intermeshed and rotate along an axis in a clockwise or anti clockwise direction. The water or fluid gets transferred by contact between the screw flights and the housing, from one screw thread to the other. The volume of fluid that can be transferred depends on the size of the pump unit, the area of the screw surfaces and the rotating speeds of rotors. Rotors in a screw pump can be timed or un-timed according to the need of the unit. For screw pumps to function efficiently, the rotors must turn at such a rate that makes each pump cavity get fully filled so that the pump works to its maximum capacity.
3. Moving Vane Pumps
This group of rotary pump has a housing that is bored in cylindrically along with an inlet for suction on one end and an outlet for discharge at the other side. An axis is placed some portions above the cylinder’s centerline. A cylindrical rotor that has a diameter less than the cylinder is driven along the axis. The clearance or gap in between the cylinder and the rotor increases from top to the bottom area. A vane attached to this rotor moves in, and then out, with rotation. This movement is responsible for maintaining sealed gaps between the wall of the cylinder and the rotor. The moving vanes help trap in gas and liquids at the suction inlet, from where, due to contraction of the space, the liquids or gas gets transferred into the discharge outlet.