| 摘要 |
<p>1,120,071. Valves. DOWTY HYDRAULIC UNITS Ltd. 19 Nov., 1965 [6 Jan., 1965], No. 649/65. Heading F2V. A bank of three linearly displaceable slide valves is provided to control the operation of double-acting jacks 51, 52 and 53 the latter of which also has a third or " float " position. A slot 44 in slide valves 33, 34 is supplied from a pump 80 via check valves 85, 86 whilst with the valves in the neutral position an " opencentre " path is formed from the pump to the tank via ports 58 in valves 33, 34 and port 66 in valve 35 to a line 76; the slot 44 in valve 35 is connected to a branch 92 from the " opencentre " path through a check valve 93. Chambers 94, 95 at the ends of the slide valves are open to the tank by passages 96-99. A relief valve 87 is included in a pump circuit. Upon moving any of the slide valves from the neutral position the associated port 58 is closed and the " open-centre " path is broken enabling pump pressure to build up at all of the slots 44 and to be directed to one or other side of the ram to be operated, the other side being connected to one of the chambers 94, 95. When the slide valve 35 is in the extreme right-hand position the ram 53 is able to '' float " since one side of the ram is connected to chamber 94 whilst the other side is open to the tank via the slot 44, a duct 71, ports 72-74 and the port 66. Each ram port may be connected to a relief valve. The manually actuated rod of each valve is provided with a centering spring. Inching slots are formed in the ends of each valve, the slots 44 and the ports 58 whilst pressure balancing ports 45, 46, 59, 60 are also incorporated although the latter port is omitted from slide valve 35, which valve embodies a spring-loaded detent. Any number of slide valves may be incorporated in a bank and certain of them may control single-acting rams or rotary motors; the slide valves may be displaceable angularly or in a rotatable manner instead of linearly.</p> |
