Shutoff head (also called "deadheading") is not good for a pump because a centrifugal pump depends on the working fluid to cool it. If no fluid is moving through the pump, it will heat the fluid and then the pump impeller, eventually causing it to fail. Since it takes time to do this, short durations of no flow can be tolerated, but longer periods can cause damage. In such a situation, engineers often install a minimum recirculating flow line. It is a small pipe with a flow orifice from the pump discharge to the pump suction. It allows a small amount of flow to move constantly through the pump, keeping cooler. The orifice keeps too much flow from going through and reducing the flow rate of the pump.