What is Shutoff?
Shutoff head is the head a pump will develop when operating against a closed discharge valve.
The point where the left side a pump performance curve intersects with the Y-axis is the shutoff condition. The head corresponding to that point will be produced when the pump is producing no flow. If a pump operates in a system that requires pressure equal or greater to the pump’s shutoff head to generate flow, the pump will fail to produce any flow.
The terms dead-heading and zero flow are sometimes used interchangeably with the term shutoff.
Operating at Shutoff
In some pumping systems, in order to purge all air out of the piping system or to minimize pressure fluctuations within the piping, it is necessary to start and stop a centrifugal pump against a closed discharge valve. During this scenario, the pump will be required to operate at shutoff for a period of time that is usually no more than 30 seconds long. The duration of this cycle should be determined in coordination with the pump manufacturer, and continuous operation at shutoff should be carefully avoided.
During the design phase of a project, a pump manufacturer should be made aware if the requirement to operate at shutoff will apply to the project. This is so that the manufacturer can ensure that the pump casing can withstand the pressure developed at shutoff and that the motor and mechanical components have been sized with consideration given to power demands at shutoff.