Washing machine valve with 3/4" MHT (male hose thread) x 1/2" MIP (male iron pipe) red handle for hot water and blue handle for cold water inlet. Water hammer arrestor cutaway. The sliding piston absorbs sudden pressure changes and keeps the pipes from banging. ... When a valve closes quickly and stops the flow, that momentum shakes and pounds pipes. A water hammer arrestor cures this condition with a cushion of air that absorbs the momentum.