The gear pump is an example of rotary pump. It is a positive displacement pump in which the pumping action is caused by the relative movement of rotating and stationary element of the pump. The gear pump draws the fluid from a chamber and can attain discharge pressure up to 200 atm. It contains no check valves and when built of proper material can be used for any liquid without suspended solids or abrasives. An efficiency of about 90% can be obtained with this pump.
The gear pump consists of two identical intermeshing gears rotating with close clearance inside suitable pump housing. One of the gears called the driver gear is connected to the input by a driver shaft. The other gear called the idler gear is mounted on a pin and is free to rotate around the axis of the pin. Power is supplied to the driver gear while the idler gear rotates relatively due to the close intermeshing. The pump is provided with airtight inlet and outlet pipes.
When the pump is operated the driver gear rotates and rives the idler gear and the movement pushes the liquid out of the chamber due to the differential pressure created on either side of the pump.
During operation vacuum spaces are formed as each pair of meshing teeth separates and atmospheric pressure forces the liquid inward to fill the gap. The liquid filling the space between two adjacent teeth is carried along with the teeth as they rotate and is forced out through the discharge opening. The liquid being pumped cannot short circuit back because of the close intermeshing of the two gears.
The advantages of this pump are low cost, simplicity in design and construction, uniform flow of fluid, silent operation and low maintenance cost. The only disadvantage is that the pump cannot be used for fluid with solid particles in them.