The hydraulic machines which converts the mechanical energy into hydraulic energy are called Pumps. This hydraulic energy is in the form of pressure energy. In centrifugal pump, the mechanical energy is converted into pressure energy by means of centrifugal force acting on the fluid.
Important Points
- The centrifugal pump acts as a reversed of an inward radial flow reaction turbine. This means the direction of flow in centrifugal pump is in radial outward direction.
- This means the direction of flow in centrifugal pump is in radial outward direction.
- Centrifugal pump works on the principle of forced vortex flow.
Main Parts of Centrifugal Pumps
- Impeller
- Casing
- Suction Pipe with a foot valve and a strainer
- Delivery pipe
Impeller
Impeller is a rotating part of a centrifugal pump. It consists of a series of backward curved vanes. Impeller is mounted on a the shaft which is connected to the shaft of an electric motor. Since the backward vanes are the most preferred vanes so they are used in impellers.
Casing
It is an air-tight passage surrounding the impeller. Casing is designed in such a way that the kinetic energy of the water discharged at the outlet of the impeller is converted into pressure energy before water leaves the casing and enters the delivery pipe.
Suction pipe with a foot-valve and a strainer
A pipe whose one end is connected to the inlet of the pump and the other end dips into water in a sump is known as suction pipe. A foot valve is one way or a non-return valve which is fitted at the lower end of the suction pipe. Foot valve only opens in one direction i.e., upward direction. We also fit a strainer at the lower end of the suction pipe for removing the impurities.
Delivery Pipe
A pipe whose one end is connected to the outlet of the pump and the other end delivers the water at a required height is known as delivery pipe.
Heads and Efficiencies of a Centrifugal Pump
Suction Head
It is the vertical height of the centre line of the centrifugal pump above the water surface in the tank or pump from which water is to be lifted.
Delivery Head
The vertical distance between the centre line of the pump and the water surface in the tank to which water is delivered is known as delivery head.
Static Head
The sum of suction head and delivery head is known as static head.
Static Head= Suction Head + Delivery Head
Manometric Head
The manometric head is defined as the head against which a centrifugal pump has to work. Manometric head can be defined as a sum of suction head, delivery head, friction loss in suction pipe, friction loss in delivery pipe and velocity of water in delivery pipe.
Efficiency of a Centrifugal Pump
Manometric Efficiency
It is the ratio of manometric head to the head imparted by the impeller to the water.
Mechanical Efficiency
It is the ratio of the power available at the impeller to the power at the shaft of the centrifugal pump.
Overall Efficiency
It is defined as the ratio of power output of the pump to the power input to the pump.