Shut Off Head in Pumps

"If the discharge of a centrifugal pump is pointed straight up into the air the fluid will pumped to a certain height - or head - called the shut off head. This maximum head is mainly determined by the outside diameter of the pump's impeller and the speed of the rotating shaft. The head will change as the capacity of the pump is altered."

This is covered in detail at this link....

http://www.engineeringtoolbox.com/centrifugal-pumps-d_54.html

Dead head is the term used. No flow.

The effect on centrifugal and PD pumps will be different.

How much detail do you require?

How much will you understand?

explain wat will be the effect in both the cases if i close the discharge end.

for positive diplacement pump it will burst the discharge line.

but what in case of centrifugal pump?

It will cause the fluid in the pump to heat up, and perhaps to boil.

A small correction in "for positive displacement pump it will burst the discharge line" is may not be exactly the discharge line but the pump casing can itself, if the pressure goes beyond the material strength. Also Depends on the location of the shut off valve (blockage) in the line. That's why a relief valve will be provided at the outlet of the PD pump.

For the case of Centrifugal pump, since it has a large space between impeller and casing, if the outlet is getting blocked, liquid will churn inside the casing.

Dear Mr.shrikant45,

You have referred "but what in case of centrifugal pump?"

CHURNING of the Fluid takes place, and the CHURNING of the fluid WILL RAISE THE TEMPERATURE of THE FLUID inside the pump.

A minimum FLOW from the pump is to be ensured, depending upon the Temp.Rise permissible.

Example: Boiler Feed Water Pump - Leak-Off Connection.

DHAYANANDHAN.S

Do not close off the discharge end of a centrifugal pump that is operating. There are multiple examples of catastrophic (explosive) failure of pumps in that condition.

Google examples for soap and sugar refineries especially.

The shut-off head of a positive displacement pump is the lower of either the pump casing rupture pressure or the downstream piping system rupture pressure. As a concept, then, it is a non-starter.

The shut-off head of a centrifugal pump is the maximum lift that the pump can achieve before its operating condition causes mechanical distress to either the pump or the fluid passing through. Do not exceed this pressure.

In either case, exceeding it is expensive in terms of lost process time, damaged equipment, rework and clean-up.

Dar Mr.shrikant45,

1.what is actually meant by shutt off head in centrifugal pumps.

Ans: The Maximum pressure developed by a Centrifugal Pump when the delivery valve is FULLY CLOSED, and NO-DISCHARGE of the fluid is allowed.

2. what is the effect if i close the discharge end of the centrifugal pumps and also positive displacement pumps?

Ans: For Centrifugal Pump - if Valve is closed - CHURNING TAKES PLACE and Temp. of the FLUID is INCREASED, depending upon the VISCOSITY, etc.

If you close the Delivery Valve of the POSITIVE DISPLACEMENT, the Casing will BREAK or the SHAFT WILL BREAK or the Motor will get TRIPPED or BURNT.

DHAYANANDHAN.S