These systems designed around the 110170, 110171, 110191, 110310 or 110315 are very common on trailers built from 1975 to the early 1990s.
The valves include a relay feature that uses tank pressure (when available) to speed release of spring brakes. As 'Service Brake Priority' valves they will charge the reservoirs and spring brakes simultaneously.
Service kits are available.
