Problem
A newly installed steam injection water heater with a ½” vacuum breaker was experiencing sporadic periods where the vacuum breaker chattered rapidly and “spit out” condensate. Once the water heater reached its set point, the chattering stopped and did not reappear for hours. Chatter will eventually destroy the cage that holds the spring and ball-check in place on the vacuum breaker.

Cause
Harmonic flow oscillations in the flow path leading up to the vacuum breaker can cause a vacuum breaker to experience chattering. One explanation for the oscillations is condensate build-up between the vacuum breaker and the steam, particularly if the unit is mounted to the steam side. Steam and air are compressible and water is incompressible, if the pipe contains air on the top, water in the middle and steam on the bottom of the standpipe, this can lead to a winding up of an under-damped mass/spring system that causes the check valve in the vacuum breaker to chatter.

Solution
Vacuum breaker chatter can be eliminated by preventing condensate build-up in the stand pipe that the vacuum breaker is mounted to. A properly installed steam trap and appropriate piping can be used to prevent condensate build-up in the flow passage leading to the vacuum breaker.