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How to use a Vacuum Breaker above design temperature?

How to use a Vacuum Breaker above design temperature?

Challenge
What to do when you need a vacuum breaker to protect your pipes and tanks and your steam temperature is higher than the temperature limit of the vacuum breaker? Kadant Johnson vacuum breakers are designed to operate up to 365°F (185°C). Some installations that require a vacuum breaker have steam temperatures that are higher than 365°F (185°C).

The vacuum breaker’s temperature limit is attributed to the Viton adhesive that anchors the vacuum breaker’s O-ring. While using a higher temperature-resistant O-ring material may help with the O-ring life, the adhesive is the temperature-limiting factor so a different O-ring material would not be of much help here.

Solution
The goal is to isolate the vacuum breaker from direct exposure to the high temperature steam by using condensate and air as a buffer. The adhesive’s exposure to the steam is reduced with a cushion of air/water between the vacuum breaker and the hot steam. For smaller vacuum breakers, use a Pigtail pipe and for larger vacuum breakers, those larger than 1”, use a P-Trap. Mount the vacuum breaker at the highest level of the tank or piping the valve is protecting.

Results
With the P-Trap or Pigtail, hot steam is kept away from the vacuum breaker and the adhesive is protected. Size the Pigtail or P-Trap to have flow area equal to, or greater than, the vacuum breaker.

vb temp drawing

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