# Water flow speed

### Water flow speed

Ok, I need help with this, and yes I did google it and found lots of info but not what I'm looking for. What I am trying to figure out is how fast as in feet per second would water flow at 40psi with no restriction at the end of the pipe?

This would be 1/2 inch PEX, if that matters, anyone here good with math?

grumpy
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### Re: Water flow speed

You need to know the length of the pex and number of fittings to figure this out.

But why would you need to know this?

steamup
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### Re: Water flow speed

I think he is referring to domestic water systems and not hydronic. ???

coalkirk
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### Re: Water flow speed

I figured he would be talking about domestic. However, there is no need to figure open flow that way. You need residual pressure at the end of the pipe to be of any use, so different design standards would apply.

The opposite approach should be taken. The pipe should be sized for the flow and pressure drop. The size should also limit the velocity to under 8 feet per second to be reasonable. 10 feet per second and more can cause errosion of the pipe materials.

However, for giggles, here is a forum that talks about the same calculations.

http://forum.pipeflowcalculations.com/v ... ?f=3&t=218

steamup
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