What is suitable distance for installing presseure transmitter after pressure control valve? or is there no consederations to get smoothly control of pressure?

 

No more than 15 metres

 

The distance should not be more...otherewise the pressure may be changed as the distance will increase...so keep minimum distance as posible

 

thank u sir. Can we install pressure transmitter before control valve? What is the advantage and disadvantages of this?

 

It all depends on which pressure you want to measure.
If you want the upstream, connect it before.
If you want the downstream connect it after.

To answer the original question, don't put it too close or you will get a lower pressure at high flow rates due to the vena contractor effect 5-10 pipe diameters should be OK

Roy

 

Dear Roy to u...

can u tell me how thats possible. as the velocity increase pressure decrease as per bernouli's equ. u r right but tell me how its apply to this case bcoz there is no change in velocity will occur, though we will change by valve is different case. but when in ideal condition my mean to say continue process. how its possible?

Mohsin

 

Mohsin,

I'm not sure that you can apply Bernoulie's equation in this case because the flow profile will not be even.

If you ever install large pressure regulators the pressure tap is usually well downstream.

I recall working in a large regulator where the pressure tap was in the body just after the seat, As the flow went up, the pressure dropped so the valve opened even further until the valve was wide open. Moving the tap downstream a couple of feet cured the problem.

Regards
Roy

 

Dear Roy

sorry but i am not getting u in this case..

perhaps we r going out of the topic. The topic was "What is suitable distance for installing presseure transmitter after pressure control valve? "

and as u told befor the distance should not much minimum becoz of the vena contractra effect. but can u tell me how this effect affact to this topic....

and i m agree wid u that x'mitter generaly applicable to downstreem but as i know it also depends upon the purpose for which ur using x'mitter......

Regards,
Mohsin

 

Mohsin,

Lets start again.

Because the flow profile at the exit of the valve may not be even (swirling) it's possible that the pressure at the top of the pipe is higher or lower than the pressure at the bottom and this may change as the valve moves from Closed to Open. For this reason you should tap into the line a few pipe diameters downstream for the pressure transmitter where the pressure has had time to even out.

I mentioned my regulator experience as an example. In that case I actually had a partial vacuum at the valve body and several psi a few feet downstream. If you put a pressure transmitter immediately after a control valve you may get an error in the reading.

Yes, If you want to know the pressure before the valve you must tap into the upstream pipe. If you want to know the pressure after the valve you must tap into the downstream pipe.

Regards,
Roy

 

Dear Roy

Thanks you for solving the quest.now i am clear in this case but tell me ur experiance in low velocity flow. is this same apply for low velocity?

and one more thing i wanna know if u want measure pressure for low velocity flow then how u measure...one technic that i know is pressure gauge. can u give me brief idea about this.....

regards,
Mohsin