Valves for Rough Vacuum Service

[code1]

Can you please recommend leads for rough Vacuum service? The valves, ranging would be gate or globe valves, sizes of 8-12" for steam condensate service, sub-atmospheric pressure, ~80 deg. C/ 176 deg. F.

All suggestions greatly appreciated.

 

[gerhardl]

This is a relatively 'not so common' service request, even if vacuum is commonly used in many processes, and products exists.

For very coarse vacuum and some leakage acceptable, you could probably get away with good, common, valves, but qualified through the supplier.

To find both a supplier that can give you a valve product performance guarantee for higher demends, and not to high price and reasonable deliverytime I would recommend you to:

a) Make out a complete, detailed technical inquiry.
b) List all technical data required (exact pressures, operating time, temperatures, material requirements etc)
c) Including best possible list of dimensions, number, operators (hand, automatic)
d) Listing seat sealing properties required for your vacuum process.
e) Most important: vacuum sealing properties for valve body sealing (if any) and stem sealing.

Please note that a common pipeline for steam, with flanges, will leak in air over time if negative (vacuum) pressure under cooling (steam condensating). Special requirements for flanges and flange sealings, or welded piping, might be required for your process.

Note that many engineers discussing vacuum use the general terms, course - or fine vacuum.

Course vacuum is usually described as from less than atmospheric, usually 1.33 times 10 in third potence millibar, down to 1,33millibar. Fine vacuum from 1,33 millibar bar down to 1,33 times 10 in minus third. And the scale continues. (Please excuse the old-fashioned nomination)

To get exact answers, for instance for stem sealing leakage resistance for vacuum, you will have to be exact, giving limits for the pressure, and describing where you are on this scale. Perhaps you don't need the whole course vacuum scale, and only for a limited process time?

Anyway, with proper formed requirements (not overdone!), you should be able to discuss your needs with a larger valve supplier or factory.

Suppliers with valves certified for 'no emission' (TA-Luft) could be possible discussion partners, but there is significant differences sometimes between sealing from inside out and outside in!

 

[JimCasey]

Normally for mere subatmospheric pressure valves as in valves that connect to powerplant condensers, normal industrial-type valves are used. It is common to use a lantern-gland packing and to flood the lantern-gland with water. Thsi reduces leakage, and anything that does leak into the process is Gland Seal Water. Also particulrly with power plants, air inleakage causes accelerated corrosion, and by supplying gland-sealed valves they avoid the corrosion problems. The gland-seal water system uses water that is clean enough so that it will not otherwise corrupt the chemistry of the system.