FAIL OPEN (FO) CONTROL VALVE

[CaracasEC]

Dear All,
Is it safe for a steam turbine driven condensate pump (centrifugal type)
and lube oil pump (screw type)to have a fail open control valve upstream
of trip valve?

Thanks in advance...

 

[BigInch]

Yes, but a fail open trip valve wouldn't be so good.

If it ain't broke, don't fix it. If it's not safe ... make it that way.

 

[bimr]

Domestic suppliers usually configure the system with that scheme. European suppliers configure the throttle valve to close. Either way is acceptable.

Forsthoffer's Best Practice Handbook for Rotating Machinery - William E. Forsthoffer

 

[CaracasEC]

Dear All,
Thank you for the quick reply, it helps me a lot.
Can i ask one more thing, how about a fail close on the cooling water supply for the bearing housing jacket?
Is it safer for these valves on the turbine bearing housing to be fail open? thanks in advance...

 

[BigInch]

Should fail to open, or simply just fail at last position, perhaps with a warning or alarm. If it failed closed, you'd probably want to tie that into a system trip. You would not want to keep running while cooling water was lost, unless you like the smell of burned bearings. Or maybe you're counting on high bearing temp alarm to shut down. In any case, and on the other hand, failing open, or at last pos, would allow you to keep running at while you give some thought to maintenance schedules, rather than dealing with a total shutdown just because some valve decided to go to sleep.

If it ain't broke, don't fix it. If it's not safe ... make it that way.

 

[CaracasEC]

Thank you very much BigInch..What if i will change the control valve with a car sealed open gate valve,
would there be a problem on the bearing?thanks...

 

[BigInch]

If the valve is to facilitate maintenance only, that would be OK. The question now is, if it is for ON/OFF maintenance purposes only, why is it presently a control valve?

If it ain't broke, don't fix it. If it's not safe ... make it that way.

 

[CaracasEC]

Thanks Big Inch, yup that is now my concerned. Why is it that a control valve is used for the cooling water supply of the bearing. On some of the design i encountered it was just a gate valve which is normally open and car sealed open. Could the reason be a possible water condensation on the lube oil cause by the flowing cooling water on the bearing housing jacket. The control valve function could be once the pump/steam turbine is not running, the control valve will be closed to avoid the possible condensation? what is your experience? thanks a lot..

 

[TD2K]

If the control valve is interlocked with the turbine, I'd suspect it's intended to conserve cooling water when you don't need it. How big is this turbine?

This is not a usual configuration in my experience, the cooling water usually just flows whether or not there is a process demand.

 

[CaracasEC]

The rated power is 43.6 kw...

 

[Pumpsonly]

My guess is to control the pressure of the cooling water to the bearing housing.. Do you have very high or fluctuating cooling water supply pressure?

 

[CaracasEC]

THe cooling water for the bearing housing is from our closed loop cooling water system header which supply all the cooling system on both the ISBL and OSBL which is stable.