Centrifugal Pump

[Shafayat Ahmmed]

Hi all,
I want to know why it is common practice to keep the delivery/discharge valve closed during start up of a centrifugal pump?
I googled this and found different answers which made me confused.
So an explanation would be very helpful guys.
Thanks

 

[3DDave]

It should take less power, but what other answers were there?

 

[Shafayat Ahmmed]

It is agreed by all that it reduces the required power. I want to know the reason behind this. Why the required power is lower when the delivery valve is closed?

 

[3DDave]

If you recall from physics class - work is a force through a distance or a change in pressure of a flowing volume of fluid across a boundary.

If there is no flow there can be no work; with no work there is no energy expended and therefore no power.

There is friction so that does take some power, but it's minimal.

 

[LittleInch]

Shafayat,

The pump forum might have been a bit better, but 3DDave has the essence of it.

Shaft power from a pump is proportional to flow x head(pressure) divided by the efficiency.

With a closed valve there is no flow, but also efficiency is low. Also there is internal flow within the pump which uses power.

If you look at any normal centrifugal pump curve you will find at no flow the shaft power is normally at the lowest.
At best this is usually about 50% of max shaft power, but often in the range 60-70% of max power at no flow.

Each pump is different so you need to look at your specific pump.
also this is for centrifugal pumps. Don't do this with axial flow pumps - their power curve goes UP as flow reduces...

E.g.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Tmoose]

Some pumps go into pretty violent recirculation when "dead headed."
Big pumps with a small number of vanes were the worst.

 

[Shafayat Ahmmed]

Thanks All.

 

[Shafayat Ahmmed]

Hi Littleinch,
Sorry for my late response.
I post again in pump community because my misunderstanding of the statement "the pump forum might have been a bit better, but 3DDave has the essence of it".
It was a mistake from my side.
Thanks for your support.

 

[horacio Torres]

The procedure to star up a centrifugal pump is:

Check the oil seal for the pump
Open the valve suction side
Star with the push bottom
Open slowly the valve discharge side
Check for abnormal noise or vibration of the pump
Open full discharge side
Check the pump seal is no leaking
the pump is alight into the process

Horacio

 

[Artisi]

I answered this previously in your second posting asking the same question - this post seems to have vanished.
Short answer is, some pumps installations start against a shut head condition, thousands of others don't, that doesn't make it common practice.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[Sanjv9473]

Centrifugal Pumps are the most popular and commonly used type of pump for the transfer of fluids. In simple words, it is a pump that uses a rotating impeller to move water or other fluids by using centrifugal force

The main important point to be noted about centrifugal pump is it is not self priming pump.

But it's use is very high in every industry.

 

[Haseen Khan]

The main reasons are

To minimize the starting torque on the motor.
To load the delivery pipe network gradually if it is the only pump that feeds the network.
If it is a parallel connected pump, this method will insure against any reverse flow due to malfunctioning of upstream side check valve.

 

[Sanjv9473]

It is common practice is , discharge vale is close when starting g of centrifugal pump because starting current is more at starting so to prevent from overloading.