A four-way spool valve assembly embodying a regenerative circuit for controlling the actuation of a double acting fluid motor for a bulldozer blade or the like characterized in that the spool has therewithin a relief valve and a check valve respectively operative to build up back pressure in the return line from the rod end of the motor during the blade lowering operation and to permit return flow under such back pressure into the inlet port to prevent cavitation of the head end of the motor, and further characterized in that the spool has a float position in which a bypass passage in the assembly is open for flow of fluid from the inlet passage to the return passage and in which both motor ports have unrestricted communication with the return passage.
A spool valve assembly (11) including a valve spool (33) defining a Raise position (R) operable to provide fluid communication from an inlet port (21) to a work port (25), and a Neutral position (N) blocking such flow. The spool valve (33) has a Lower position (L) in which return flow from the work port (25) flows past a pilot operated check valve (77) is then metered by a metering notch (75) defined by the valve spool. The valve spool (33) also has a separate Float position (F) in which the inlet port (21), the work port (25) and the return port (23) are interconnected. In the Float position (F), fluid at the valve spool (33) is in communication with the return port (23) through a back-pressure valve (59), which may be manually adjusted to control the back-pressure on a work implement (15) as it is permitted to "float".
5168705 - Hydraulic drive system - Owned by Hitachi Construction Machinery Co., Ltd. (Tokyo,JP) Kayaba Industry Co., Ltd. (Tokyo,JP)
A flow control valve has a first variable restrictor to control a flow rate of a hydraulic fluid supplied from a hydraulic fluid supply line to a hydraulic actuator and a second variable restrictor to control a flow rate of the hydraulic fluid discharged from the hydraulic actuator to a hydraulic fluid return line. A pressure compensating valve holds constant a differential pressure across the first variable restrictor, and a recovery circuit having a recovery line has a check valve that allows flow of the hydraulic fluid only toward the supply line. The recovery circuit receives at least part of the hydraulic fluid discharged from the hydraulic actuator and returns it to the supply line at a portion between the pressure compensating valve and the first variable restrictor through the recovery line upon controlling of the discharged flow rate by the second variable restrictor to thereby recover the discharged hydraulic fluid. A third variable restrictor disposed in the return line at a portion downstream of the second variable restrictor controls the recovery pressure of the hydraulic fluid returned to the supply line, and its restriction amount is changed dependent upon an input amount of the flow rate control valve.
A device is disclosed for controlling a double action working cylinder (10) having a piston (11) with a piston rod (12) on a single side by means of a multiple-way valve (19), in which the available forces are to be fully applied at the beginning of the extension of the piston rod (12) and the differential motion becomes effective after a fixed distance of displacement of the piston. The multiple-way valve (19) has seven connection openings (T1, A1, P, B1, A2, T2, B2) for driving the predetermined functions, which can be driven in the individual working position by means of a valve piston (20) provided with seven control edges (1-7).
