Assuring sealing with bellows for critical control valves

[jalvarez]

Hi mates:
Your opinion or experience:
For a control valve in a vapor anhidrous hydrogen chloride service, (minus 32°F - 170 psig), is it reasonable to use a metal bellow for sealing the stem to the atmosphere, additional to the conventional sealing system?
I think that the efectiveness of a metallic bellow for sealing in a control valve is doubtful, as the bellow is exposed to a continuous movement (due to the modulation of the control valve). So, it will have a short life, I suppose.
Any suggestion?
Thanks
J. Alvarez

 

[moltenmetal]

The trouble with anhydrous HCl is that any leakage will combine with atmospheric moisture to generate strong acid which may attack the stem and rapidly make the leak worse.

A fugitive emissions bonnet with a dryer/acid indicator on the sniffer port would be the minimum I'd want.

There are some brands of bellows-sealed control valves out there which can give considerable bellows life. There are also small packless control valves which eliminate the whole problem if your flows are small enough.