A valve assembly including a non-planar valve head adapted to be fitted to a supply line, wherein: the valve head is adapted to reciprocally travel along a longitudinal axis , supported by a shaft longitudinally aligned parallel to a general direction (A) of water flow from the supply line in use; and the valve head includes a wall terminating in a peripheral sealing contact surface for sealing engagement with a valve seat of a valve body of the valve assembly , the valve seat defining an aperture in the form of a valve opening that, in use, is adapted to be continuous with the supply line when the valve assembly is in an open position, the wall extending inwardly from the peripheral contacting surface towards the shaft , wherein: the wall is dome-shaped and in the form of a skirt ; the peripheral sealing contact surface is in the form of a terminal edge that is formed from a downwardly depending edge of the wall ; the width of the terminal edge corresponds to or is narrower than the wall thickness; and characterized in that the valve head is adapted to axially shift towards downstream to an extent that its displacement distance is of a magnitude at least one quarter of the diameter of the valve opening to provide sufficient clearance by the valve head . wherein: the valve head is adapted to reciprocally travel along a longitudinal axis , supported by a shaft longitudinally aligned parallel to a general direction (A) of water flow from the supply line in use; and the valve head includes a wall terminating in a peripheral sealing contact surface for sealing engagement with a valve seat of a valve body of the valve assembly , the valve seat defining an aperture in the form of a valve opening that, in use, is adapted to be continuous with the supply line when the valve assembly is in an open position, the wall extending inwardly from the peripheral contacting surface towards the shaft , the valve head is adapted to reciprocally travel along a longitudinal axis , supported by a shaft longitudinally aligned parallel to a general direction (A) of water flow from the supply line in use; and the valve head includes a wall terminating in a peripheral sealing contact surface for sealing engagement with a valve seat of a valve body of the valve assembly , the valve seat defining an aperture in the form of a valve opening that, in use, is adapted to be continuous with the supply line when the valve assembly is in an open position, the wall extending inwardly from the peripheral contacting surface towards the shaft , wherein: the wall is dome-shaped and in the form of a skirt ; the peripheral sealing contact surface is in the form of a terminal edge that is formed from a downwardly depending edge of the wall ; the width of the terminal edge corresponds to or is narrower than the wall thickness; and characterized in that the valve head is adapted to axially shift towards downstream to an extent that its displacement distance is of a magnitude at least one quarter of the diameter of the valve opening to provide sufficient clearance by the valve head . the wall is dome-shaped and in the form of a skirt ; the peripheral sealing contact surface is in the form of a terminal edge that is formed from a downwardly depending edge of the wall ; the width of the terminal edge corresponds to or is narrower than the wall thickness; and characterized in that the valve head is adapted to axially shift towards downstream to an extent that its displacement distance is of a magnitude at least one quarter of the diameter of the valve opening to provide sufficient clearance by the valve head . <EOS>