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I have a problem that I think I can easily fix with a restricting orifice. The problem is, I am not sure how to go about sizing it, as I have never done it.

I have a tank that is vented to atmosphere, that is fed by a 2" water line. water pressure is 120 psi at the inlet, and I want to knock it down to roughly 80 psi, but I would prefer to not use a regulator. I am looking for a quick and inexpensive way to reduce water hammer when the feed valve closes. We have a regulator in now, but I would prefer to use a restriction, so I can eliminate the regulator.

Would a restricting orifice work in limiting the line pressure feeding this tank, since I am only trying to limit the flowing pressure? If so, what size bore would I need? If anyone knows where to find a free software package for this, please let me know.

Try http://3d2f.com/tags/restriction/orifice/design/
They advertise free software downlosd
I'm not sure it will give you what you want though as the pressure drop is dependent on the flow rate, as the valve closes the orifice will have less drop. Usually the orifice is placed downstream of the valve, it's a common way to reduce cavitation. If water hammer is the problem you might get better results with a speed control valve on the actuator so that it closes slowly'

Regards
Roy

Hay,

Dear orifice sizing is as simple as 123... I think you may know the Bernoulli equation. Just apply it as you have upstream pressure [120 PSI] and downstream pressure [80 PSI]. You also know the pipe diameter [2"]. The more inputs you have to know are as given below:
1-Flow for which you want to size orifice
2-Operating temperature of the fluid
3-Density

When you have this information you can calculate the orifice dia. through modified Bernoulli equation for orifice given in a no. of chemical engineering handbooks, or you can also derive it by yourself from the general Bernoulli equation. I hope this may help to resolve your problem. Take care and be happy.