Watts 800M4 QT pressure vacuum breaker. Production began in 1994. This is a bronze bodied unit. The check spring is contained. The check seat is replaceable. A seat removal tool is needed. The test cocks for this model are located on the ball valves. The 800M4 is a redesign of the 800M2 and 800M3 series with the addition of a replaceable check seat. In 1995 the 800 M4 FR model was introduced. This model contains a small relief valve built into the air inlet float to prevent damage if it freezes.