| 摘要 |
<p>1,212,989. Pressure control systems. INTERNATIONAL BASIC ECONOMY CORP. Dec.22, 1967 [Dec.29, 1966], No.58371/67. Heading G3P. A pilot-operated unloading valve for a pump can respond directly to high rates of change of pump delivery pressure above the level at which the pilot valve is actuated. As shown, the pump delivers into line 213-A and, when the pressure reaches a predetermined level, pilot spool 210 is depressed to allow flow to drain via restriction G2 and lines 214, 211-A. This flow produces a pressure drop across restriction G2 and the downstream pressure acts via restriction G3 in chamber 272 below spool 222. The chamber 220 above spool 222 senses pump delivery pressure through restriction G5 and a restriction G6 in parallel with check valve 219. Thus, during relatively slow variations in pump pressure, spool 222 is subjected to the pressure difference across restriction G2 and moves downwardly to connect line 216 to drain to limit the pump pressure. However, during rapid pressure fluctuations, restriction G3 is effective to allow spool 222 to respond to the fluctuations as communicated to chamber 220. A capacitive oil-filled chamber 270 or a cylinder with a spring-biased piston communicates directly with chamber 272. When the pilot spool is in its upper position, it connects line 213A to chamber 272 via line 207 so that pump pressure acts on both ends of spool 222. In the modification of Fig.16, not shown, spool 222 controls the flow to and from a pump unloading mechanism. In Fig.17, not shown, the pilot spool only controls the flow to drain. A separate pressure responsive (300) controls the flow to a line 207-B corresponding to line 207 above.</p> |
