A. Centrifugal Pumps
Definition:
It may be defined as one in which an impeller rotating inside a close fitting case draws in the liquid at center and by virtue of centrifugal force throws out the liquid through an opening at the side of casing.
Centrifugal pumps are most widely used in irrigation practice. They are simple in construction, easy to operate, low initial cost and produce a constant steady discharge. This type of pump is well adapted to usual pumping services such as irrigation, water supply and sewage services.
Principles of Operation:
A centrifugal pump is rotary machines consisting of two basic parts:
1. Rotary element or impeller, and
2. Stationary element or casing
Principles:
The underlying hydraulic principle is the production of high velocity and the partial transformation of this velocity in pressure head.
Impeller is a wheel or disc mounted on shaft and provided with a number of vanes or blades surrounds the impeller.
In some pumps, a diffuser consisting of series of guide vanes or blades surrounds the impeller
Operation:
The pump is filled with water and the impeller is rotated. The blades cause the liquid to rotate with the impeller and in turn impart high velocity to the water. Centrifugal force causes it to be thrown outward from the impeller in to casing.
Outward flow through impeller reduces pressure at the inlet allowing more water to be drawn in through suction pipe. Due to conversion of high velocity into pressure, water is pumped through discharge pipe It is done either in volute casing or in diffuser casing.
Techniques Used for Priming:
A foot value to hold the water in pump.
An Auxiliary pistons pump to fill the pump causing and suction line with water.
Connection to an outside source of water under pressure for filling the pump.
Use of self- Priming construction.
B. Vertical Turbine Pumps:
Vertical turbine pump [deep well turbine pump] is vertical axis centrifugal or mixed flow type pump comprising of stages which accommodate rotating impellers and stationary bowls possessing guide vanes.
These pumps are used where the pumping water level is below the limits of Volute centrifugal pump. They have higher initial cost and are more difficult to install and repair. The pressure head developed depends on the diameter of impeller and the speed at which it is rotated. The pressure head developed by single impeller is not great. Additional head is obtained by adding more bowl assemblies or stage.
Construction:
It has three parts:
1. Pump Element:
The pump element is made up of one or more bowls or stages. Each bowl consists of an impeller and diffuser.
2. Discharge Column:
It connects the bowl assembly and pump head and conducts water from former to later.
Discharge head:
It consists of base from which the discharge column, bowl assembly and shaft assembly are suspended.
C. Submersible Pumps:
An vertical turbine pump close coupled to a small diameter submersible electric motor is termed as “submersible pump”. The motor is fixed directly below the intake of the pump. The pump element and the motor operate under submerged condition. It can be used in very deep tube well where a long shaft would not be practical.
Construction:
It consist of pump and motor assembly, a discharge column, a head assembly and a water proof cable to conduct the electric current to a submerged motor.
Pump element:
It consists of propelling shaft, usually made of stainless steel and bronze impellers. Water enters the pump through a screen located between motor and the pump.
Electric Motor:
The motor is enclosed in steel case filled with light oil of high electric strength. A mercury seal placed directly above the amateur prevents oil leakage or water entrance at point where the drive shaft passes through the case to the impellers.
