GB856302A - Improvements in and relating to apparatus for delivering liquids at a constant mean rate - Google Patents

Abstract

856,302. Liquid meters; valves. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Nov. 14, 1958 [Nov. 14, 1957], No. 35516/57. Classes 69 (2) and 135. Apparatus for metering liquid at a controlled mean rate comprises a free piston 12 in a cylinder 11 and a system of valves 13-16 operated at predetermined intervals by timing means to allow liquid from a pressurized source to pass alternately into opposite ends of the cylinder, thus displacing the piston and discharging liquid from the other end of the cylinder. The liquid is supplied to the apparatus from a reservoir 23 which may be pressurized or located high enough to provide sufficient head or a pump 22 may be provided. The valves 13-16 comprise short lengths of polyvinylchloride or other flexible tubing which are nipped in pairs (e.g. the inlet valve 13 to one end of the cylinder and the outlet valve 16 from the other end) by an arm 17 or 18 which is pressed on the tubes by springs 17a or 18a, but can be raised when an electromagnet 19 or 21 is energized. To compensate for slight variations in thickness of the tubes, the arms 17 and 18 are slit to form two prongs or, alternatively, abutments against which the tubes are pressed are made resilient and, to avoid liquid bypassing the cylinder, the valves are arranged so that each pair of valves closes not later than the other pair opens. For timing the valve operation, a clockwork switch may close a contact at regular intervals of, say, half a second and, to vary the intervals, the time switch may operate through a cascade of relays having a selector switch by which intervals of ¢, 1, 2 or 4 seconds may be chosen; alternatively, the time switch may act through a multibank uniselector, a set of stepping relays or an electronic multivibrator. The maximum rate of operation of the valves must not exceed the rate at which the supply pressure can drive the piston so that the piston waits at each end of the cylinder until the valves change over. By providing interchangeable pistons of different lengths, the volume displaced per stroke can be altered. The cylinder may be made of transparent material so that movement of the piston can be checked visually and the piston and cylinders heads are arranged so that the valve ports are sealed at the ends of the piston strokes, the sealing being improved by a resilient ring round the port or in the end of the piston. Where the liquid being metered is radio-active, the reservoir and other parts of the apparatus may be shielded and a switch may be provided for opening all four valves when it is desired to wash out the apparatus.