Patent ID: 7958909

Claim:
A two stage spool valve comprising: in a single assembly; a first stage spool moveable between first and second positions, the first position coupling a source of fluid under pressure to a first hydraulic area associated with a second stage spool that is moveable between third and fourth positions, and the second position coupling the first hydraulic area to a vent, the second stage spool having an outer diameter defining a second stage spool cross sectional area; the first hydraulic area being disposed so that fluid under pressure acting against the first hydraulic area encourages the second stage spool to the third position; a second hydraulic area coupled to a source of fluid under pressure and disposed to encourage the second stage spool to the fourth position; the first hydraulic area being larger than the second hydraulic area, the first and second hydraulic areas both being smaller than the second stage spool cross sectional area; the second stage spool being configured to couple a first port to a second port when in one of the third and fourth positions and to not couple the first port to the second port when in the other of the third and fourth positions; the first and second spools being cylindrical spools, each having at least one groove in its outer diameter cooperatively disposed with respect to at least one port in a respective housing in which the respective spool can slide to hydraulically communicate with and block hydraulic communication between the respective groove and port, depending on the position of the respective spool.