This is a pressure-actuated unloader that is designed for any pump that fits within the flow and pressure range of the unloader.  The unloader regulates the flow in the system and maintains system pressure via an adjustable nut that controls the amount of tension on a pressure spring.  When no flow is going out the outlet port, all flow is diverted to the bypass port at virtually no pressure.  The unloader is capable of handling one or more shut-off guns and should be run with no bypass (if the full flow from the pump is going through the unloader).  It actuates at around 10% above the system pressure.
 
US
Metric
Minimum Flow
2.2 GPM
8.3 L/min
Maximum Flow
13 GPM
49.2 L/min
Min Pressure
375 PSI
25.9 bar
Max Pressure
3000 PSI
200 bar
Temperature Rating
160 °F
70 °C
Inlet Port
 
1/2" FNPT 
Outlet Port
 
1/2" FNPT 
Bypass Port
 
1/2" BSP 
Weight
2.8 lbs.
1.3 kg