On Monday, May 29, 2017 at 7:39:40 PM UTC-4, wrote:
On Monday, May 29, 2017 at 7:20:01 PM UTC-4, wrote:


If there is no flow, there will be no pressure differential. Pressure will be the same throughout the volume of liquid from inlet to outlet.

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Ed Huntress

If you have a column of water, the pressure at the bottom of the column in higher than the pressure at the top. So there is an example of no flow with a pressure differential.

Oh, right. I was thinking of externally applied pressure. Gravity or centrifugal force would result in a differential.

Any pressure applied from the inlet, as in the case of a multi-stage centrifugal pump, would be the same throughout the volume within one involute. But the centrifugal force added by the spinning rotor would be greatest at the periphery.


If you take something like say a large nut and tie a string to it and whirl it around your head, then you have a force on the string and a velocity of the nut. But the nut does not go flying off , unless you let go of the string.

In the same way with the outlet blocked off on a centrifugal pump. the water has a velocity , but it just goes around and around. Produces a pressure, but no flow from the pump.

Again, the velocity is the tangential velocity. There is no radial velocity.


Think of a centrifuge with test tubes in it. The material in the test tubes are subjected to force, but there is no flow.

Dan