The Hydraulic Valve is an automatic urinal flush control valve. The valve uses a unique and simple mechanism which prevents water waste by ensuring that the autoflush cistern is only filled, and can only flush, when the washroom is used. The Cistermiser Hydraulic Valve is installed on the supply pipe to the urinal cistern. The valve is activated by short-term pressure drops created by use of taps or WCs on the same supply. The valve is normally closed; when it is activated it opens and water passes to the urinal cistern until the pressures on both sides of the valve are equalised. When the cistern is full, the auto-siphon will flush. The installer or user can adjust the time the valve remains open and therefore how long the cistern takes to fill and how much water is used. When the washroom is not being used the water supply pressure remains constant and the valve remains closed, preventing water passing into the cistern. The cistern can therefore only flush during periods when the washroom is in use, eliminating unnecessary water consumption and cost.