Flow direction of Globe valves

[Isha90]

Material Body F91, Disc F316+St6, Stem XM19
Could anybody clarify how flow over the disc will avoid unseating due to differential thermal expansion when compared to flow under the disc.

 

[LittleInch]

A diagram would help -a lot.

also a bit more context.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Isha90]

Usually for low temp. flow is under the disc, but our case Valve is for Steam service where temp is 540°C.
Please refer for fig,

https://www.globalspec.com/learnmore/flow_control_flow_transfer/valves/globe_valves

 

[gerhardl]

If you mean that your valve is mounted with stem down, this is normal for steam valves, especially for high-temperature applications.

The main reason is that high-temperature air rises. This will give an updraught of air with cooling effect at the valveside mounted down, and a heating effect at the side mounted up. At this temperature you want to protect the spindle windings and spindle sealings and mount this side down.

Is this an answer to your question?

 

[Isha90]

Thank you,standard T-Globe with flow under disc, Stem & Hand wheel top normal Flow axis horizontal
1. Will there be steam leak at disc seat in this flow direction[Flow under disc],
2. Should we reverse the flow direction [Flow over disc] to stop leak
3. During which condition should we consider flow over disc.

 

[LittleInch]

not really enough information here, but If I understand what you're saying

1) If you can't supply enough pressure on the disc from the actuator to seal then yes, but it might just be the disc / seat is damaged
2) You can, but there is no guarantee of success and then it becomes harder to open the valve. The valve needs to be designed and constructed in this manner otherwise the disc might be forced off the end of the stem. Is the valve good for bi directional flow? Is there a flow arrow stamped on it or attached with a plate?
3) When the valve is designed that way

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[gerhardl]

In addition to the facts that LittleInch mention, you should als note following points:

- At 540 degC you will at some points have a very high delta P across the seat and valve.
- At high differential pressure steam will fast (by cavitation) enlarge even the tiniest haircrack over the seat sealing surface.
- A flow direction helping closing the disc might help, but not necessarily in any significant way.

To me it sounds like it will be better to try a valve with a more suitable seat, cone or regulating seat, minimizing the the seat wear (cavitation) when you open and close, and give a better thightening geometry. Use a high-quality version from a specialized steam valve producer.

 

[Isha90]

Thank you