Adjustable inlet valve with air gap

An inlet valve controlling the introduction of fluid into a vessel, said vessel forming a reservoir for the fluid and having an inlet admitting replacement fluid from a fluid supply into the vessel to replace fluid discharged from the vessel by flow of fluid from the supply inlet of the vessel through the inlet valve, said inlet valve comprising a valve body member and a movable valve element that is movable with respect to the valve body member between a first position corresponding to a closed condition preventing flow of fluid through the inlet valve and a second position corresponding to an open condition allowing a flow of fluid through the inlet valve to replenish or replace the supply of fluid within the vessel after discharge of fluid from the vessel wherein there is a clearance portion associated with the valve body member or the movable element, said clearance portion being arranged such that when the movable element is in closed position within the inlet valve there is a space or gap between the movable element and valve body member allowing flow of gas into and/or through the valve between the movable element and the valve body member so as to provide a facility of or for a gas gap in the valve wherein the gas gap prevents unwanted flow of liquid from the vessel into the supply of fluid when the inlet valve is in the closed position.