Fisher pneumatic Control Valve Plug detachment

[Daren Samy]

I have seen three times that Plug has been detached from stem of pneumatic control valve. There are three provisions for plug and stem connection.
1. Plug has threaded hold in which thread stem passes through.
2. There is provision of Nut at the end of stem. This but seats on the plug and holds the stem tightly.
3. Diagonal pin that passes press fit through plug and hardly touches stem (may be to avoid rotation of stem)

Why this design of stem is showing failure of plug detachment?
Why not weld the stem and plug to avoid detachment ?

 

[itsmoked]

Got a picture?

Use the

to post it.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Daren Samy]

No ! I have no picture

 

[gerhardl]

Difficult to answer without a picture of the construction. Generally a stem ought to have a secure connection to the plug with no risk for accidental loosening, even by long-term use or wear. Obviously your valves does not have this construction. The why is therefore probably cheaper, not higher class products.

On the other hand a flexible (but solid and wear resistant) connection between plug and stem will prevent the bending (and wearing) forces a long and stiffer construction will have at the small differences in alignment moving up and down.

 

[Daren Samy]

Good point ! Stem has threaded connection with plug. If I weld the stem with plug, will it be not safe?

Daren!

 

[TugboatEng]

There needs to be flexibility between the stem and disk to allow for misalignment between the stem and seat. If you make the stem to disk connection rigid your valve may not seat correctly and you won't be able to achieve shut-off. For a control valve this may or may not be a problem.

 

[SPDL310]

Are the valves you are seeing this failure on configured similarly to the valve in your other post on the stem nuts? Have you contacted Fischer for their recommendations? I would suspect improper nut tightening, excessive seating force or a combination of the two may be the cause of your failures.

 

[Daren Samy]

SPDL310 ! Stem nut post does not pertain to any failure. Fisher control valves have experienced plug detachment problem. I could not take pic due to urgency of work and installed it back after necessary repair. I would share drawing of valve to seek further opinion on repeated issue.

Daren!

 

[CptMaaB]

Dear Daren Samy, it would be good if you could share the drawing.
It would help to get things clearer.