American Lube 635040 ARO-STOP ValveAmerican Lube 635040 Aro Stop Shut Off Valves Are Designed To Prevent Pump "Runaway". Pump Runaway Occurs When The Material Container Is Depleted, Causing The Pump To Cycle Fast And Needlessly. The Aro Stop Valve Protects The Pump By Shutting Off The Air Supply When The Material Container Is Empty Or A Fluid Line On The Outlet Side Of The Pump Is Broken. Use With Oil Or Grease Pumps. Aro Stop Valve For 2" &Amp; 3" Thunder Pumps, Series 200 Pumps &Amp;