isolation valve

[kdashc]

would anyone suggest using an isolation valve at a pump discharge as a means of controlling operating pressure in a closed system

 

[iken]

Has anyone thought of just a simple Isolating Regulating Valve. I cannot see where it was implied the valve had be be lectrically controled (a control valve), just the pressure controlled (constant?)

 

[BigInch]

There isn't any such thing as an isolation-regulation valve, or isolation-control valve. The two terms have inherently opposite meaning. Isolation means closed, cut-off, shut, continuity broken, positive closure, whereas a pressure or flow regulator provides its functions when somewhere between full closed and full open. A control valve, and especially a regulator, is NEVER considered as having positive shutoff, even if it is deactivated in the closed position, therefore they cannot in any form or fashion double as an isolation valve.

**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch

http://virtualpipeline.spaces.live.com/

 

[ScottyUK]

That's an interesting comment that there isn't any such thing. I say 'interesting' because on some steam turbines the main stop valves are used for control during acceleration, with a transfer from MSV control to governor control at sync idle speed. An unusual case perhaps, and certainly a highly specialised valve, but they are designed to control and they do provide positve shutoff with 100+ Bar steam at 500C. The exception which proves the rule?


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If we learn from our mistakes I'm getting a great education!

 

[zdas04]

I've seen those valves, but every time there is also a big ass gate valve just upstream.

Throttle valve that actually shut off flow are common. Throttle valves that can be counted on to shut off flow are nonexistent. I've seen hundreds of globe valves that actually give you a bubble-tight seal and dozens of globe valves that leak like a barn door, but I still stand by the statement that it is poor design to rely on them for isolation.

David

 

[BigInch]

I suppose technically a valve in a transition state, even if its an "isolation" valve, is throttling something .. for a few seconds or so.

OK. I'll give you that one.
Now I see that your globe is malfunctioning.

**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch

http://virtualpipeline.spaces.live.com/