Abstract: A valve for controlling purging fluid for marine speedometer lines includes a valve body. The valve body has a bore extending in a longitudinal direction therein, a speedometer port, a pressurized fluid supply port and an impact tube port. The ports are spaced apart in the longitudinal direction and communicate with the bore. A valve spool is slidably received within the bore for reciprocation between first and second positions in the bore. The spool has three spaced apart seals between the bore and the spool. There is a first passageway between the first and second seals and between the spool and the bore. The speedometer port and the impact tube port communicate through the passageway, the pressurized fluid supply port is isolated from the speedometer port and the impact tube port, and the third seal and first seal are on opposite sides of the pressurized fluid supply port, in the first position of the spool.