A 50-Year History of the Extended Bonnet Cryogenic Valve

by Jack Bonn, Eden Cryogenics, LLC, jbonn@edencryogenics.com

Many cryogenic products have been developed out of necessity over the past 50 years. One such product is the vacuum jacketed extended bonnet cryogenic valve. Currently there are numerous manufacturers in the US and abroad that have utilized design basics developed over 50 years ago. One of the main contributors to the current design basics was CryoVac/CVI (CVI).

CVI was committed to the space race in the 1960s and involved in designing and building space simulation equipment. This included LN₂ shrouds, LN₂ subcoolers, 20K helium refrigerators, vacuum jacketed piping and related components such as bayonets and valves for cryogenic systems. Standard equipment was being designed to meet the cryogenic applications for space simulation during this period of time. One example of equipment used for vacuum jacketed piping was a close tolerance bayonet connection developed by Dr. Herrick L. Johnston in the late 1950s for primarily liquid hydrogen service. The length of the male and female bayonet connection reduced the heat input to the cryogenic fluid considerably more than mechanically insulated field joints. The Johnston bayonet design became a standard connector for shop fabricated, evacuated, tested and sealed vacuum jacketed piping. Pipe spools were shipped to the job site and the bayonet joints were joined together, eliminating field welding between the pipe sections. The bayonet design became the root of the development of the CVI extended bonnet cryogenic valve. The two main commonalities between the bayonet and the cryogenic valve with an extended bonnet is a warm O-ring seal and the close tolerance fit between the valve barrel and extended bonnet, which reduces heat input to the cryogenic fluid.

The first valves CVI used in cryogenic service were extended stem valves with the bonnet flange part of the valve body as shown in Figure 1 (C) and required a cold bonnet packing/seal. These valves are still used in many cryogenic applications today where heat leak is not a critical part of the requirement. The problem CVI had with these valves was they were very difficult to service if mechanically insulated as shown in Figure 1 (A), with the bonnet connection insulated. In some applications all valves are gathered together in an enclosure and foam insulated. Problems occurred when a valve seat would become damaged by metal shavings or other debris in the system and needed to be serviced. Removing the foam to access the seat and plug created a major maintenance issue in addition to the large heat leak in major systems with many valves.

To avoid service problems and improve performance, the cryogenic valve bonnet flange was separated from the valve body and extended approximately 12″ from the body as shown in Figure 2 (D). The stem diameter in Figure 2 (F) was made larger than the valve plug. This was the major change in cryogenic valve design that occurred approximately 50 years ago and made the valve better suited for cryogenic fluid transfer, especially for colder fluids such as hydrogen and helium. In the original design Figure 1 (B) the stem diameter is smaller than the valve plug and requires the body to be split to service the plug. The modified cryogenic valve with the extended bonnet flange is easily incorporated into vacuum jacketed piping with stem extension vacuum insulated as shown in Figure 2 (E).

Prior to extending the bonnet flange from the valve body, existing valve manufacturers such as Powell, Crane, Jenkins, NIBCO, Newco and others provided cryogenic rated valves, which most of them were already providing for other applications, with an extended stem that could not be vacuum jacketed. The production requirement of cryogenic valves in the 1960s at CVI was about 200 per year in valve sizes from 1/2″ to 2″ NPS, and it was not in the best interest of the large valve manufacturers to add this modification to their standard valve line for this reduced production rate.

CVI started modifying existing manufacturers’ valves by removing the flange at the body casting and extending the stem approximately 12″ to meet design requirements necessary to vacuum jacket the valve, including the extended stem. These modifications reduced the heat leak, made it easier to service and maintain and allowed incorporation of valves in a static vacuum jacketed pipe. However, it proved to be costly to continue to modify existing commercially available valves. CVI engineering personnel were commissioned to develop a line of cryogenic valves.

This effort began in 1964. CVI developed sizes from 1/2″ NPS to 2″ NPS globe valves for cryogenic service as shown in Figure 2. It took approximately four months to complete this project with minimal cost. Flow tests to establish the valve CVs were conducted at the Ohio State University by Dr. Chuck Sepsy on linear, equal percentage and on-off flow plugs. This new cryogenic valve was well publicized in the CryoVac/CVI catalog and documented in books such as “Cryogenic Systems” by Randall F. Barron, “Cryogenic Engineering” by Russell B. Scott and the Instrument Society of America’s “ISA Handbook on Control Valves” edited by J. W. Hutchison. None of the cryogenic valve manufacturers’ valves were considered or defined as trade secrets or patent worthy or secret in any way. The CVI design for the extended bonnet cryogenic valves was for manual operation with provisions for pneumatic actuator installation on the bonnet. Other valve manufacturers developed their own line of similar cryogenic valves with some differences in the valve body design, valve plug design or method of bolting or clamping the bonnet to the extended bonnet flange.

There were several reasons for CryoVac/CVI to develop the extended bonnet valve.

1. Servicing the valve became easier using the extended bonnet valve.
2. Installing the extended bonnet in a vacuum jacketed pipe spool, incorporating the valve within the same vacuum as the pipe spool, improved the performance of the valve and also protected it from any corrosive environment.
3. Heat leak of the valve incorporated in a vacuum jacketed pipe or vacuum jacketed cryostat or valve box was reduced.
4. Incorporating the valve within the pipe spool at the factory reduced the overall field costs and decreased the potential of damage to the valve during installation.
5. The valve assembly is an all welded construction for use in a static vacuum system with the bonnet flange extended away from the valve body, versus the typical valve that has the mechanical split body connection as part of the valve body.
6. O-rings in the bonnet flange and stem seal were at ambient temperature during all operating conditions for greater reliability.
7. The stem extension was made with thin wall tube or pipe that is a close tolerance fit within the extended bonnet to eliminate any thermal oscillation and lower the heat leak.

The close tolerance, extended bonnet style vacuum jacketed cryogenic valve has a more than 50-year history in the cryogenic equipment market and is widely used throughout the United States and most foreign countries. This modification of extending the bonnet flange has proven to be highly efficient, reliable, durable and versatile for use with all cryogenic fluid operations.

References

1. Randall F. Barron, “Cryogenic Systems,” published by McGraw-Hill Series in Mechanical Engineering, 1966.
2. Russell B. Scott, “Cryogenic Engineering,” 1963 edition, reprinted in 1988 by Met-Chem Research Inc.
3. J. W. Hutchison, ed., “ISA Handbook of Control Valves,” published by Instrument Society of America, 1971.