The H-5 Relay Valve comes in several models as listed below with each being unique to the intended operation and are not interchangeable. It is important to change out with the same model as removed as this will cause the system to not function properly if not changed like kind. Externally the models look alike but have internal variations. The model number is steel stamped in the side of the mounting flange for correct identification.
> H-5 10# > H-5-B 25# > H-B-5 10#
> H-5 25# > H-5-B 50# > H-B-5-D 8#
> H-5 50#
> H-5 60#