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View Full Version : Static Head

Darrell D
June 26, 2015, 01:50 PM
OK this might not be the right place for this but there a lot of Civil Engineers on these forums so I'm giving it a shot. No text books or other materials seem to quite cover this situation as it occurs in the world.

All on the discharge side: If a pump is at an elevation of one hundred feet, the highest point in the line is at 120 feet, there is a low spot at 80 feet, and the line discharges at 110 feet, what is the static discharge head?

I know what my answer is but there are a couple of answers that differ from mine. Thoughts?

Patrick Moore
August 6, 2015, 11:25 AM
Darrel,

I think a lot would depend on what exactly the configuration of the system was. Is this in a closed pipe between the suction and discharge point so its pressurized flow the whole way? Is there an air release/ vacuum release valve at the high point? Is there a valve at the receiving point that would provide backpressure against the high point to keep it going to vacuum? Does the line from the high point to the discharge drain once the pump stops? Does the water flow by gravity in a free surface from the high point? All those would impact the development of a system curve and what the static head would be.

From and engineering standpoint, I would consider the static flow based on what happens at flow = zero. At zero flow (i.e the static head) just to move the water, the pump would have to lift the water 20 feet to get the water over the high point. However, once the water is moving and all the air is out of the line the water could have a siphon created which would impact the pump operation and the system curve. At that point, the static lift could more likely the head difference between the suction and the receiving point for governing the flow. It would depend on whether a siphon could be created or not and if the water discharged below the water surface and if the flow from the high point to the discharge was full. But if no siphon is able to be created and the line from the highpoint to the discharge runs as a free surface, then I would say the static lift would remain 20 feet as the pump would be working against that as it ran.

Anyway, thought I'd add my thoughts to the discussion. I'm curious to see other responses as well.