It is difficult to calculate a precise sub-cool temperature. Sub-cool is the difference in temperature that causes the bellows
to actuate. If the load temporarily exceeds the capacity of the trap, backup occurs. The trap opens, but the temperature continues
to drop until the cycle is exhausted. The average sub-cool for the –B2 bellows was 2.3 °F for 20 psig, 1.75 °F for 25 psig,
1.45 °F for 30 psig, and 1.0 °F for 35 psig. The –B bellows has an average sub-cool of 2.0 °F. The maximum sub-cool for the
B bellows is 3.4 °F for 20 psig and 1.5 °F for 35 psig. The maximum sub-cool for the –A bellows is 5.3 °F.
An Orifice Trap is Not a Steam Trap
The Nicholson Steam Trap Company's model CDS steam trap with a type –B bellows has proven itself in laboratory tests to be
sensitive enough to maintain backup below 6 in. for loads ranging from 1 to 27 lb/h, encountered during SIP maintenance of
vessels ranging from 20 to 40,000 L.
These laboratory results are encouraging and the next step is to repeat these results in a field setting. Field data will
offer a high degree of assurance of the trap's performance, so facilities can be designed around steam traps with a 6 in.
George W. Page, Jr., is director of engineering for Spence Engineering Co., Inc., 150 Coldenham Road, Walden, NY 12586; 845.778.5566, fax: 914.778.1930; email@example.com
Richard Kral is a lead process engineer at Jacobs, BioPharm Office, Three Tower Bridge, Two Ash Street, Conshohocken, PA 19428, 610.832.2625, fax 610.238.1100, firstname.lastname@example.org
1. Fluid Controls Institute. FCI 87-1-2004, Classification and Operating Principles of Steam Traps. Cleveland OH; 2004.
2. Lydersen BK, D'Elia NA, Nelson KL, Oakley T. Bioprocess Engineering: Systems, Equipment, and Facilities. Hoboken NJ: John
Wiley & Sons, Inc.; 1994, p. 515.
3. Fluid Controls Institute. Tech Sheet #ST 101. Some Usage Consequences with Orifice Drain Devices (Valuable Design Considerations
for Engineers, Designers, and Steam Users). Cleveland OH; 2003 August 20.