Flow responsive latch for holding a spool valve in an open position

A valve 10 includes a body 14 with a spool bore 18, a supply passage 30, a tank return passage 32, and a workport 40, 44. A spool 16, in the spool bore, has a first position providing a first path between the supply passage and the workport, a second position providing a second path between the tank passage and the workport, and a neutral closed position. While the spool is in the second position a latch assembly 60 is responsive to pressure in a control passage 88, so that fluid flowing from the workport to the tank passage produces a first pressure, which exerts a force on the latch to inhibit spool movement; and when the fluid flow from the workport to the tank passage terminates, a second pressure is produced causing the latch to allow spool movement. The latch mechanism can comprise of cam 76 coupled to a latch piston 78 and spheres 122 engaging with notches 72. The cam engages with the spheres to lock the spheres in the notches and hence the spool in the second position, until the pressure change in the control passage overcomes the force of detent spring 112 to release the spool.