Pressure drop across valve

[gasoperations]

If a high pressure system ( say 9 barg ) with high flow ( say 2000kg/Hr ) is discharging into atmosphere through a 2" gate valve and a small length of pipe ( Small friction drop ).

Will the pressure drop take place across the valve or the flow will choke at the end of the pipe.

Thanks

 

[Latexman]

Yes, pressure drop will take place across the valve. Choking is most likely to occur at the point of minimum inside diameter. Most gate valves are considered full bore. therefore choking could reasonably be expected at the end of the pipe.

Good luck,
Latexman

 

[gasoperations]

Thanks Latexman

But if it is required to maintain a certain low back pressure on the valve outlet ( say 0.1 barg ). Is it possible to achieve that.

Actually this is a requirement from a depressurizing system where vendor has specified low back pressure for the vent valve.

I am not able to imagine how this can be achieved if choking will take place at the exit ( therefore there will be high back pressure at the valve outlet. )

Thanks

 

[MikeClay]

As long as the valve backpressure is below the valve’s choke pressure, it will have no effect on the depresssuring rate. Initially the backpressure could be as high as 4.5 bar and not affect the flow (assuming gas). As the equipment is depressured, the flow will decrease and along with it, the backpressure will decrease. Given that this is a short run of pipe, there should not be a problem. But a quick sanity check of the backpressure should be done.

--Mike--