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The Mysteries of Cryogenic Component Installation Revealed
San Luis Obispo, CA – Installation of components for vacuum jacketed applications just got easier. There are several twists and turns in the road to getting it “right” so to help reduce frustration over placement and location, Cryocomp has developed detailed instructions for various components used in vacuum jacket piping and cold box applications. These instructions (included below) will help save time, money and aggravation by answering your design questions, minimizing the possibility of incorrect installs and maximizing the performance and function of the components.
VACUUM SEAL OFF VALVES
These valves must be installed no closer than 6” to 8” from a jacket termination or any other cold location. (Fig 1) The vacuum seal off valves have O-ring seals and with excessively low temperature, they will shrink and allow leakage into the vacuum space. It is also good practice to install the vacuum seal off valve somewhere near the center of the vacuum mass.
Orientation on the pipe is not critical, but to assure future servicing of the vacuum, the vacuum seal off valve should be in a location that will allow a valve operator to be installed after the pipe is in service. (Fig 2)
BAYONETS
Vertical bayonets must be installed with the male above the female, no exceptions. (Fig 3) For best thermal results it is necessary to have the flange or closure junction and seal at the upper most location and the cold interface at the bottom. This forms a gas pocket between the liquid interface and the O-ring which keeps the seal at a nearly ambient temperature.
Horizontal bayonet sets can be installed with the male either up stream or down stream. (Fig 3) Industry convention has generally located the male upstream, but it does not physically or thermally make a difference. On all bayonets, be sure to lightly grease the O-ring seal with a system compatible grease. This allows the O-ring to establish a much tighter seal. With the CB7 style bayonets, be sure the knurled nut is tight to 5 to 10 ft-lbs.
Flanged bayonets, be sure to grease the O-ring seal with a system compatible grease. After tightening the V-band tension nut, tap the outside of the strap at several points around the OD with a plastic hammer to firmly seat the “V” section on the flange and then re-torque the nut. (Fig 4) Repeat this process at least 2 more times.
VACUUM JACKETED VALVES
All cryogenic valves should be installed with the stem or bonnet extension above the liquid line. This is to keep a gas cushion between the liquid pool and the upper seals. Valves are usually installed with the flow direction going from under the seat to over the seat which assures no pressure on the packing when the valve is closed. Reversing the flow through the valve, over the seat however, is sometimes necessary for specific applications and will not affect the flow capacity. For example, a Y pattern valve in a vertical pipe below the supply with the flow going down, as in a service drop, will have the flow going over the seat. (Fig 6)
Globe valves, those with the stem vertical to the flow path can be installed with the bonnet extension rolled to an angle not more than 60 degrees off vertical. The packing is still above the liquid line. (Fig 5)
Y pattern valves have the stem extension at a 45 degree angle to the flow stream. These valves are ideal for location in a vertical or service drop. The Y pattern valve can also be used in a horizontal line as long as the packing is above the flow line. Y pattern valves usually have a better flow coefficient than the equal size globe valve.
Angle valves (90 degrees) are sometimes used in place of a vertical elbow. (Fig 7) The same rules apply, you can tilt the stem section up to 60 degrees off vertical and flow across the seat either direction is ok.
VAPOR VENTS
The purpose of a Vapor Vent (also called Keepfull and Cryo Vent and a host of other names) is to vent vapor and keep liquid. (Fig 8) Vapor Vents are used to discharge boil-off gas and maintain liquid at some place in the system usually far away from the liquid supply. These devices must be vertical, above the pipe section and should be installed at a high point where gas would gather in the system.
About DLH Industries, established in 1994, DLH Industries specializes in developing and manufacturing the Cryocomp product line of cryogenic and high vacuum valves. DLH Industries offers reasonable pricing, excellent service and has earned a reputation of high quality products which are second to none in the industry. DLH Industries continues to grow and expand their product line to meet client applications and industry standards. For a complete product list and more information visit www.cryocomp.com.
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