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Water pipe inrush force

Water pipe inrush force

Water pipe inrush force

(OP)
I've got a 6" elbow on a pipe section. The pipe is normally empty. When activated, the water rushes in at a rate of 1000 GPM in 1 second.
I need a way to calculate the "shock load" as the water hits the elbow.
Has anyone dealt with this before? It's and above ground fire suppression system.
Thanks.

RE: Water pipe inrush force

FBD?

RE: Water pipe inrush force

At that rate, I would treat the length of pipe upstream of the elbow as a solid mass, then F=ma, with m=rho V of the pipe between the valve and the elbow.  a=change in velocity from zero to whatever velocity corresponds to 1000 gpm in 1 second (a large number).  

I find this approach supportable if not rigorously accurate because shock waves and echo's during the first few hundred milliseconds make the wave front look something like a solid mass.

David

RE: Water pipe inrush force

I would use F = rho.A.v^2 and a dynamic amplification factor of 2. F is the component force assuming a 90 deg. bend, then Fres = sqr root(2F^2).  

RE: Water pipe inrush force

Just a reminder that rho is mass density, not weight density.

Ted

RE: Water pipe inrush force

hydtools,
I'm really curious as to why you felt that your post was necessary?  I don't see anything above that would indicate that any of us were in immanent danger of getting that wrong, did I miss something?

David

RE: Water pipe inrush force

That was for the original poster.  You contributors need no reminder.  Other posts have had long discussions on using mass versus weight so I thought I would simply place a reminder.  Not an admonition.

Ted

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