5 replies to this topic

[rodolfoingeniero]

Hi Everybody,

Does anybody know whether an on off valve may be considered as a control valve?

I need technical argument since our instruction to bidders indicates that control valves operated from emergency shut down system must be specified having double solenoid valve and redundant.

Our refinery requires that on off valves must be specified having double solenoid valve and redundant.

Contractor argues that instruction to bidders was not clear enough since it indicates control valve rather than on off valves, therefore we will have to pay an additional for that.


Best Regards.

[mishra.anand72@gmail.com]

consider on off valve as control valve??

Nobody has said that before.

Ur instruction to bidder is to use control valves for positive isolation in case of emergency?? Is ur control valves tight shutt off valves?? To which standard u will adhere??

Why u instructed?? what does it mean??

Forward it to finance. Why they can not pay?? Is it because of slowdown/recession?? Why politicians or managing directors not loosing jobs in that scenario?? Why job cutting down the line only??

[riven]

Contractor argues that instruction to bidders was not clear enough since it indicates control valve rather than on off valves, therefore we will have to pay an additional for that.

Seems perfectly clear to me. the wrong valves were specified and thesefore extra work has to be done to incorporate the correct valves.

An on/off valve should never be used as a control valve directly. It may control indirectly by closing a bypass line or preventing something from happpening by opening or closing something (i.e. on or off control) hence the name.

The question you have to ask is whether to original spec for control valves is correct or if the on/off valve spec is correct.

[rodolfoingeniero]

Hi Riven,

Thanks form your prompt response.
You really got the question.
We do know an on/off valve should never be used as a control valve directly.
We do know the right valve in this service must be an on off valve.

The point in this situation is purely semantic since instruction to bidders indicates "control valves operated from emergency shut down..." while the right wording should have been "on off valves operated from emergency shut down..." or just "valves operated from emergency shut down...".

That is the point.

Then, may the wording "control valves operated from emergency shut down..." be understood as "on off valves operated from emergency shut down…”?

[riven]

Then, may the wording "control valves operated from emergency shut down..." be understood as "on off valves operated from emergency shut down…”?

I would say no as control valves never equal on off valve in good practice. So I would side with the contracter if I were PM. Mistakes happen.

[djack77494]

rodolfo,
As riven has stated, control valves are NOT on/off valves and on/off valves are NOT control valves. When your specification stated that "control valves operated from emergency shut down...", the vendor was right to be confused. In an ideal world, he/she would have contacted you for clarification, pointing out the discrepancy. My viewpoint is that the vendor was wrong to have not done so, and that your spec writer was wrong to have misstated the requirement. It's hard to say who is more to blame, but I would put more blame on your company. When you connect "control valve" with "emergency shut down", that should be a clue that this valve must have an on/off function. However, it could still be a modulating control valve with a fail position that is activated during an emergency shutdown. Good luck in untangling the mess.