The VRT3-310A Unloader with 4,500 max PSI, 10.5 max GPM and 3/8"F outlet, black spring and no adjustment knob. The unloader valve diverts water flow into bypass when the trigger gun valve is closed. Unloaders may be designed to respond to either an increase in pressure or a change in flow. The unloader valve may also be used for variable pressure adjustment. This unloader is one of the most popular and reliable unloaders on the market. 
If Easy Start feature is required, use alternate unloader with EZ Start valve: VRT3-310EZ
 
SPECIFICATIONS
Max GPM10.5Max PSI4500Inlet2x3/8" FOutlet3/8" FMax Temp194° FBy-Pass2x3/8" FSpring ColorBlackKnobNo