Q.centrifugal pump

Each centrifugal pump consist of components such as
shaft, bearing, structure and sealing arrangement.
It converts energy of a prime mover to kinetic energy and then to pressure energy with help of volute casing. The impeller of centrifugal pump is the rotating parts which converts shaft energy to K.E. of fluid.
Diffuser or volute casing is the stationary part of the pump that converts these K.E. to pressure energy.
What makes a centrifugal pumps distinctive is that
it often run in either direction with its radial and axial flow styles. Other major factors that makes it totally different than that of a positive displacement pumps are;
a)performance,
b) fluid viscosity and
c) working.
The impeller suck in water creating a minor vacuum by adding kinetic energy to the water or fluid. It is then regenerate to pressure energy with the assistance of volute casing or diffuser.
On alternative hand a positive displacement pump force a restricted quantity of liquid cornered within the system towards discharge port.
While in positive displacement pumps the flow remains same regardless of pressure, flow rate do change with pressure in centrifugal pump.
The drawback with centrifugal pumps is that it can’t handle high viscous fluids whereas the positive displacement pumps don’t have any problem pumping them out.

Q.What is cavitation, and it’s causes and remedies?

Cavitation will be occurred once the pump suction contains air or once the pump is running quicker than the designed speed.
Low pressure regions occur within the flow at points wherever high native velocities exist.
If vaporisation occur due to low pressure areas then bubbles formation occur, these expand as they move with the flow and collapse once they reach at area of high pressure area.
Such formation and collapse of bubbles terribly|is extremely|is incredibly} fast and collapse close to a surface will generate very air mass hammer blows which ends in corrosion, noise, vibration, and fall off in the pump efficiency.
So the pump must be run at designed speed and strangling of the suction valve ought to be avoided

2.What is the procedure of overhauling of centrifugal pump?

1.Put off breaker and take away fuse from motor starter box
2.Close suction and discharge valve
Remove suction and piping rim bolt & nut, coupling bolt of motor coupling
3.Remove pump foundation bolts pump from motor
4.Remove impeller lock & nut & take out the impeller
5.Remove mechanical seal.
6.Remove bearing cowl from different facet shaft with roller bearing
7.Renew mechanical seal and bearings if required.
8.Clean and inspect all parts and assemble.

Q. Why Discharge Valve are Closed During Starting

A centrifugal pumps usually started with discharge valves shut. Considering the properties of centrifugal pump by operating characteristic curve it is clearly found that; when the amount of water delivered is zero, the power available is at minimum. So discharge valves valve remains shut off throughout the beginning to take care of low power demand by the pump on its motor having low power output at the beginning.
This helps stabilizing pumps at the starting. When the pump is stable the discharge valves opened and high power avaibility meets the high power demand; which might be not possible for the motor to fulfill for the starting 4-5 seconds.

Or

It is a common practice to start large capacity centrifugal pump with the discharge valve closed. If the characteristic curve for a centrifugal pump are examined it will be seen that when the quantity of water discharged is zero the power required by the pump is zero or very small amount. by starting the pump with discharge valve closed the power demand made by the pump on the pump motor is kept to very minimum after the pump has started and the momentary high motor current demand has stabilized the discharge valve is opened.

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