Steam traps are part of a steam-in-place system. The current design allots 18 in. of vertical leg for condensate backup. A design with a sensitive bellows has been proven in laboratory tests to need only 6 in. of vertical leg during the 15 min. of 121°C sterilization. Loads of 1 to 27 lb/h are covered by the capability of the new trap, equivalent to required steam for vessels 20 to 40,000 L.
Biopharmaceutical facilities include hundreds of sanitary steam traps. Steam traps require an 18 in. vertical leg for condensate backup during steam-in-place sterilization (SIP). This adds 18 in. to the elevation of equipment, portable vessels, utility panels, and clean room ceilings. The vertical leg is required by the original equipment manufacturer to guarantee that the condensate backup does not reach the temperature instrument that is monitoring a SIP.
THERMOSTATIC TRAP MECHANICAL FUNDAMENTALS
A diagram of a thermostatic sanitary steam trap for vertical installations is shown in Figure 1. The working element in this trap is an alcohol-filled bellows. When this bellows is in contact with steam, the alcohol expands, which forces the plug into the seat and stops the steam flow. When cooler condensate hits the trap, the alcohol condenses, which contracts the bellows, pulls the plug off of the seat, and allows the condensate to be purged from the trap.
The trap operates on the difference in temperature between the steam and the condensate. This difference is referred to as the sub-cool of the steam trap. As condensate backs up above the trap, its temperature drops. A trap with a high sub-cool requires the condensate to back up a greater height to allow it to cool. The piping immediately above a steam trap is uninsulated so the condensate can cool quickly. Steam traps located in a cramped, hot mechanical space where heat cannot be dissipated will not operate properly. This is a bad facility design and should be avoided.
The range of temperature in SIP is 259 to 280 °F, corresponding to 20 to 35 psig. The trap has a passive way to determine when the condensate is subcooled. Steam pressure squeezes the bellows, which is counteracted by the vapor pressure of the bellow's fill to compensate for the condensate temperature. Proper design of a steam trap can reduce the sub-cool, making it more sensitive to condensate backup. This sensitivity is controlled by the mechanical properties of the bellows and the bellows fill.