GB917904A - Improvements in or relating to hydrants - Google Patents

Abstract

917,904. Hydrants. MERRYWEATHER & SONS Ltd. Oct. 4, 1961 [Oct. 17, 1960], No. 35533/60. Class 69 (1). A hydrant valve has an hydraulic actuating device interposed between the hydrant valve member 5 and a valve-operating member 1 is so controlled by the pressure in the outlet side of the valve that it allows the valve to open when the outlet pressure is relatively low, but exerts a thrust tending to shut the valve which increases as the outlet pressure increases and thereby emits the outlet pressure. In the cylindrical skirt of the valve member 5 a piston 8 of the actuating device can move freely subject on its upper side to pressure from contact with the valve operating stem 1 and on its underside to hydraulic pressure conveyed by way of a channel 16 and a flexible pipe 9 from a cylinder 12 in the valve wall 3. When the stem is unscrewed to open the valve, the valve 5 will normally be lifted off its seating by water pressure as in Fig. 2. The hydraulic pressure in cylinder 12 is controlled by a piston 14 whose head 11 is subject to the water pressure in the outlet chamber 24 so that if the latter pressure is excessive the valve 5 is pushed down on to its seat 6, even if the operating stem 1 was previously withdrawn to an open position as in Fig. 2. A relief valve 19 can open if the pressure does not decrease when the valve is back on its seating. When the stem 1 is screwed down, as in Fig. 1, a projection 21 on the relief valve contacts the bottom of the stem and opens the valve 19 to admit water from the pressure inlet 22 into the cylinder 12 which returns the piston 14 to its normal position. Specification 854,004 is referred to.