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Posted by: charles s on 2009-02-25, 19:12:51
OK, head is pressure or velocity or static height of water. So if a pump has a specific performance curve at a constant speed, then the discharge head will equal the suction head plus the point of operation on the performance curve. That point will be determined by the flow rate because the performance point is a combination of the head and flow rate for that impeller and speed. Shut-off head is the head when the pump is running and no flow is occurring, the discharge is stopped. It is usually the highest head that the pump is capable of generating but in actuality will be a bit lower. So if you had a pump with minimal flow, the discharge head would be the shut-off head plus the suction head. What also is important is that the suction head can become negative and if the pump is primed properly it will act with a negative starting suction head. But that is limited to an atmosphere of pressure, around 32-34 feet of water column. In practice the total head a system sees will determine the flow rate and so while you would like to be able to say that the system will flow a certain rate, if your total head is higher, the flow rate will be less. It works like that. I used to do this for a living. |
