3 replies to this topic

[LeoLeo]

Hello all,

 

I have questions regarding the split range on two control valves in parallel (known as split range).

On the P&ID I see two parallel control valves A and B which discharge of both goes to same location, fuel gas system.

 

Description

 

I know that this configuration of control valve is used when required turn-down ratio is not covered by Cv range of one control valve. Therefore, we consider two control valves, one with small Cv covers low range of turn-down and the control valve with high Cv covers high range of turn-down.

For more clarity I added small sketch of system. Failure position of both control valves is fail close.

 

My questions;

 

1.     What I have seen so far is that in normal operation only one of the control valves will be fully open (depending on process throughput). Have you seen same configuration of control valves but both control valves are fully open in normal condition?

 

2.     Based on your experience, if we have faulty pressure transmitter would it be possible that both control valves go fully open (based on what I described in Description section). The answer will help to decide if existing safety valve has enough capacity or not for loss of automatic control system (PT failure)

 

 Sketch.pdf   34.66KB   30 downloads

 

Thanks!

 

ARM

[latexman]

2. Both control valves can go open.

[fallah]

ARM,

 

1- If normal conditions is accompanying with maximum expected flow through the main line; yes, both CVs might go fully open...

 

2- Yes, it might be...

[breizh]

Hi ,

Yes can go open because of flowrates, because of transmitter failure or lack of energy on the valves ( air or power supply) depending how you define the position open or close due to lack of energy.

Hope this helps

 

Breizh