| 摘要 |
<p>1413689 Valves CATERPILLAR TRACTOR TRACTOR CO 13 Dec 1972 [13 Dec 1971] 57581/72 Heading F2V A control valve for an excavator includes two open-centre spools 42, 44 moving in parallel bores 58, 60 interconnected by a through passage 78. The spool 42 controls flow between a first inlet passage 76, exhaust passages 64, 66 and work ports 172, 174. A second inlet passage 72 normally communicates with exhaust 88 but on operation of the spool 44 check valve 184 opens to allow the fluid from inlet 72 to combine with that from inlet 76. Spools 42, 44 are mechanically coupled to move together. Work ports 172, 174 communicate with relief valves 176, 178 and anti cavitation valves 180, 182. Two further spools 38, 40 are provided each with their own relief and anti cavitation valves and inlet, exhaust and work passages. The two further spools have separate inlets 68 and 70 and the spool 40 is pilot pressure operated. Spool 40 will use both inlet 68, 70 if spool 38 is not operative and similarly spool 42 will use all three inlets if spools 38, 40 are not operative. Spool 40 which is to control track motors is provided with a pair of pressure regulating overspeed valves 136, 138. All the spools are centred by conventional end spring mechanisms (not shown). Spool 42 may have a separate inlet of its own. In a modification Fig. 7 (not shown) the bore 60 receives two separate spools (238) (248) one (248) of which acts to combine the inlet flows and the other (238) of which acts to connect inlet passage (236) to a further spool valve inlet (244) via a check valve (242). The spool (248) and spool 42 are hydraulically or mechanically coupled or alternatively spool (248) is independently operable for when fluid is available at the second inlet (246).</p> |
