Fire hydrant drain valve to prevent freezing - has weighted sliding valve stem closed by water pressure during operation

摘要

The vent valve to prevent a fire hydrant from freezing is fitted in the main pipe at a boss (6). The valve body consists of a hollow cylinder (5) screwed onto the boss. The valve plate (10) is connected to the rod (11) and supports the return weight (12) which keeps the valve opened when not under pressure. The valve closes on the seat (8) on the inner side of the cylinder. Fluid is exhausted through the vent passages (9) behind the valve.