GB965656A - Improvements in or relating to pressure responsive valves - Google Patents

Abstract

965, 656. Fluid-pressure servomotor control systems. PRATT PRECISION HYDRAULICS. March 24, 1961 [April 12, 1960], No. 13012/60. Heading G3P. In a pressure responsive valve for use in a pressure system 36, 38 connected via check valve 37 to a pressure source, e.g. a pump 35, rising pump pressure acting via restriction 31 in chamber 15 keeps main spool valve 4 closed as shown with its end 23 connected to drain at 11 via auxiliary spool valve 5. As the system pressure increases via 39, 12, valve 5 is shifted against spring 21 to close drain 11 and allow system pressure to act at 23 and balance valve 4 which is held closed by a light loading spring 16. When the pump pressure opens the adjustably spring loaded relief valve 34, a pressure fall downstream of restriction 31 at 25, 10, 15 unbalances valve 4 which moves against spring 16 and connects the pump to drain via 25, 10, 11. When the system pressure has fallen to the setting of adjustment 22 of spring 21, spool 5 closes, disconnects spool 4 from system pressure and connects it to drain at 11 whereby spool 4 is balanced since its spring end has also been connected to drain, so that spool 4 closes under its spring 16 and the pump again operates on load. Relief spool 32 controlled by pilot valve 34 is well known and takes no essential part in the apparatus, but the valve 34 allows the cut-out pressure of the pump to be independently adjusted, while adjustment 22 allows the cut-in pressure to be independently adjusted. Line 25 may be dispensed with and relief valve 34 and restriction 31 incorporated in the main and auxiliary spool housing (Fig. 3 not shown).