6 replies to this topic

[irshadaliii]

dear all
please help me to tell me that why we use reducer and expander in a pipeline when we installing a control valve in that line.
i means that suppose line is of 12 inch, if we install a control valve in that line then we reduce the dia of that line upto 6 inch or 4 inch, in the upstream of the control valve and we use reducer for this purpose but in the downstream line of the control valve we use expander in that line upto 12 inch.

thanks,,,,

[S.AHMAD]

Dear Irshad
1. Let me answer your question by asking you three questions.
2. How did you get the pipeline size of 12"?
3. How did you get the control valve size of 6" or 4", why not use 12" control valve?
4. How did you connect the 12" pipeline to the 6" control valve?
5. If you can answer the three questions, then you should be able to figure out the answer to your question.

Edited by S.AHMAD, 05 March 2012 - 08:49 PM.

[salman.azim]

dear Mr. S ahmad

i couldnt understand your explanation, plz give ans in detail if possible.
thanks

[Narayanan.u]

Hi,

See the attached file, you may find the answer.

Regards,


Narayanan

Attached Files

•  valvselc.pdf   78.06KB   110 downloads

[Dmitry]

For control pressure in your line probably you don't need to have 12" control valve, so you can reduce size of your control valve. How much you can reduce the control valve - all depends from your calculations. It is a typical situation for control system.

Regards,
Dmitry

[Dacs]

Dear Irshad
1. Let me answer your question by asking you three questions.
2. How did you get the pipeline size of 12"?
3. How did you get the control valve size of 6" or 4", why not use 12" control valve?
4. How did you connect the 12" pipeline to the 6" control valve?
5. If you can answer the three questions, then you should be able to figure out the answer to your question.

Quoted for emphasis.

I think what he's trying you to do is to analyze the system so that you'll know the reasons behind the sizing of pipeline and control valves.

But if you can't, let me answer it for you.

Normally, control valves are sized smaller (which are sized based on Cv, which is ultimately dictated by flow and required pressure drop) than piping (which is usually sized for pressure losses or velocity limitation).

And of course, any mismatch in piping fittings will require reducers.

To that effect, it's haphazard just to pick out a control valve off the shelf, matching it with the pipe size and expect it to work as intended. Control valve selection requires analysis (by the very least) of:
1. Flow rate required
2. Expected pressure drop

Hope this helps

[S.AHMAD]

1. TQ Dacs, you have given the right answer.
2. I was hopping that you learn more by analyzing and answering the questions