Pilot Operated Spool Valve

A spool valve assembly for controlling fluid flow comprising:

• a body defining:
• a chamber having first and second ends
• a spool input port for fluid communication into the chamber;
• a spool output port for fluid communication out of the chamber;
• a reference inlet port for fluid communication into the chamber and
• a reference outlet port for fluid communication out of the chamber;
• and
• a spool having first and second ends disposed in the chamber for sliding movement between a first position which allows fluid flow from the spool input port to the spool output port and a second position which restricts fluid flow from the spool input port to the spool output port, the spool being positioned by differential pressure across the spool between a first volume of fluid, at a command pressure, disposed between the first spool end and the first end of the chamber and a second volume of fluid, at a reference pressure, disposed between the second spool end and the second end of the chamber, the reference inlet port and the reference outlet port both being in selective fluid communication with the second volume of fluid, one of the reference inlet port and the reference outlet port having a first flow capacity when the spool is in the first position and the one of the reference inlet port and the reference outlet port having a second flow capacity when the spool is in the second position, such that the reference pressure is changed by changing the position of the spool.