A pump is a device that is used to move liquids. A water pump displaces water by physical or mechanical action.
Different types of water pumps include positive displacement pumps. This type of pump causes liquid to move by trapping a fixed amount of it and then forcing it into a discharge pipe.
A positive displacement pump can also have an expanding cavity on the side that has suction and a decreasing cavity on the side that discharges.
As liquid flows into the pump the cavity on the suction side expands and decreases on the discharge side causing the liquid to be forced out. Given each cycle of operation the volume is constant.
This type of pump can be classified further depending on the kind of mechanism it utilises. For example:
- Rotary
- Internal gear
- Screw
- Shuttle block
- Flexible vein
- Sliding vein
- Circumferential position
- Helical twisted roots
- Liquid ring valve pumps
Positive replacement rotary pumps use the principles of rotation to move liquid. The rotation of the pump causes a vacuum which draws the liquid out. This type of pump is very efficient as it removes air from the lines automatically which eliminates the need for bleeding.
However this type of pump does have disadvantages. The clearance between the outer edge and the rotating pump must be very close meaning that they must be operated at a slow steady speed. If they are operated at too high a speed this can cause erosion in the mechanism which makes the pump less efficient over time.
Positive displacement rotary pumps are generally grouped into three different types. Gear pumps are the least complex type. They consist of two gears laid side by side with enmeshed teeth. A current traps liquid between the teeth as the gears move away from each other. Small teeth maintain a constant flow of fluid whereas large teeth cause a gushing effect.
Screw pumps are more complex and feature two or three screws with opposing threads. One screw turns clockwise and the other turns anti clockwise. The screws are mounted on shafts that run parallel to each other. The shafts also have gears which mesh with each other in order to turn the shafts together and keep all the components in place. The turning of the screws draws the fluid through the pump. As with many types of pumps the distance is small between the pumps parts and the casings.