Improvements in or relating to non-return valves

摘要

922,411. Fluid-pressure servomotor control systems. J. BLAKEBOROUGH & SONS Ltd. March 7, 1960 [March 6, 1959], No. 7797/59. Class 135. A non-return valve 12 normally acts under the control of a dashpot piston 28 to which it is connected. A valve spindle 22 is provided with ports 36, 38 for by-passing the dashpot, the ports 38 normally being closed by a valve member 42. In the event of a sudden drop in pressure on the upstream side of the valve 12, a signal is sent to a solenoid-operated valve 78 which is actuated to admit a fluid pressure, different from that passing through the valve, to the top of piston 52 causing this piston and hence a rod 58 to move downwards. Downward movement of the rod 58 first depresses the valve 42 to nullify the dashpot and then acts on the spindle 22 to move the valve 12 towards a closed position, which valve is finally closed by the fluid pressure downstream of the valve. A cylinder 50 housing the piston 52 is open at its bottom to atmosphere and the piston seats on a knife edge 64 in its lower position. When the piston is so seated there is a small clearance between the rod 58 and the valve spindle 22 when the valve 12 is closed. The valve is described for use in the bleed line of a steam turbine where the solenoid is actuated by a governor in the event of a sudden increase in speed. The valve member 12 may be provided with a skirt portion which enters the seating. In this position shown, the end of the rod 58 forms a valve to prevent leakage past this rod, which is also formed with a labyrinth seal or a water seal. If the non-return valve is used to control sub-atmospheric pressures the rod 58 is secured to the piston 52 which is spring-loaded to its upper position.