Mecline VRT3-250 pressure actuated unloader valve w/pressure switch.  One of the best unloaders on the market.  Pressure switch closes when spraying and opens when unloader is in bypass mode.  ...

Giant 22913A pressure actuated high flow unloader.  Ideal for multi-gun use. Repair kits available. 1/2"FPT Inlet, Outlet and Bypass 160 Fahrenheit Max Temp. 3500PSI Max 13GPM Max 2 - 1/4" FPT...