9mm Shower Trap with Non-Return Valve 9mm x Spring Loaded Non-Return Valve with 1.5" Solvent Weld Outlet Socket Overall height 53mm The valve acts as a non-return valve, the weight of the water discharge will open the valve and it will reseal when the discharge has ceased thus prohibiting foul air from entering the dwelling The valve eliminates the release of foul air due to back flow The valve can be easily removed to facilitate easy cleaning of the trap