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Some people say that because the flow is large, the pressure is low. Is that right? Why does the pressure drop when the flow rate is high?

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    $\begingroup$ If I have a water sprinkler being driven by water pressure in a hose, and I cut the hose, the water pressure in the hose drops - resulting in a high flow rate at the rupture - and the sprinkler stops working because lack of water pressure. I would argue the rupture caused the low pressure - then the large flow rate occured at the rupture. $\endgroup$ – Cinaed Simson Jun 27 at 2:51
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    $\begingroup$ Using a living body makes this difficult, because a standard homeostatic mechanism says – "vessel ruptured? Shut down the blood pressure to minimise leakage!". It's called the vagus reflex and some people get it if a needle pierces a blood vessel for about 50 seconds, even if nothing leaks out. So there is more than just physics here, there is biology. $\endgroup$ – Martin Kochanski Jun 27 at 10:54
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You can have high pressure and a high flow rate...

The pressure needs to be sufficient to overcome the losses in a system.

If a pipe or vessel ruptures then the losses are reduced and the velocity will increase, while the pressure reduces.

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