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# Pressure & flow calculations

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## Pressure & flow calculations

(OP)
Typically Sulfuric Acid is unloaded using 20 to 30 psi air. When tnaker truck is towards the end of the unloding Sulfuric Acid there is a 5000 gallons of compressed air at 30 psi. This builts up pressure in the tank as vent is not sized to take the pressure builtup. Can someone tell me how to calculate the vent size. The vent size shall be big enough to relieve the air as well as pressure builtup.

### RE: Pressure & flow calculations

Area of flow (in2 or mm2) = Mass rate of flow (lb/h or kg/m3) divided by Mass flux (lb/in2.h or kg/mm2h) with a factor for coefficient of discharge, and for adjustment of units of calculation.

When in doubt use a standard gas nozzle calculation which can be found in many text books.

Gas flow can choke through the nozzle. I assume you would be aiming for non-choking flow i.e. a nozzle large enough to prevent choking. Then you must ask what if acid passes through the nozzle? Where do you discharge the spillover.

For design Codes try
API RP 520 Design of pressure relieving systems in refineries.

If you contact your Valve Supplier they can do the calculation for you. Alternatively try Valve Manufacturers in the Internet.

### RE: Pressure & flow calculations

(OP)
John,

Thanks for the reply.

Shahhk

### RE: Pressure & flow calculations

This question is very similar to Sam01's question, which I have attempted to answer above.  Maybe my answer to his question can help you as well.

Haf

### RE: Pressure & flow calculations

I am trying to prove that a pipe I have would not be capable of passing 3000 gallons of DI water in 2 hours.  What equations and measurnments do I need.

Thanks

### RE: Pressure & flow calculations

To comment on the question, we'd need:
What size pipe is it
how much pressure drop do you have available
is the pipe horizontal or do you have static head effects to include and
what is the total equivalent length of piping (straight pipe plus fittings)?

From there, any hydraulics book will have equations or charts.

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