Yuken Logic Valves
These valves are comprised of cartridge type elements and covers with pilot passages. Although they are two-port valves designed to simply open/close the poppets according to pressure signals from the pilot line, various types may be combined for direction, flow rate, and pressure control. Standard covers, which have several pressure signal ports and control valves, including pilot operated relief valves, are available for control purposes.
The covers are spigot mounted so that there is no risk of external oil leakage.
Logic valves provide fast-response, high-pressure, and high-flow control. They are typically applied to machines that involve high-speed actuator operation, such as die-cast machines, injection molding machines, and press machines. In addition to the general logic valves shown in Fig. 7.1, servo-valve-integrated logic valves, consisting of a cover and a proportional valve or a servo valve, are available for highly accurate control. Such a logic valve accurately determines how much the logic valve opens, based on a deviation between the feedback signal from the displacement sensor on the main spool and the input signal to the proportional or servo valve.
The logic valves have the following features.
(1) Multifunction performance in terms of direction, flow, and pressure can be obtained by combining elements and covers.
(2) Various functions can be achieved, depending on the pilot line connection.
(3) Poppet-type elements virtually eliminate internal leakage and hydraulic locking. Because there are no overlaps, the response time is very short, permitting high-speed shifting.
(4) For high pressure, large capacity systems, optimum performance is achieved with low pressure losses.
(5) Since the logic valves are directly incorporated in cavities provided in blocks, the system faces fewer problems related to piping such as oil leakage, vibration, and noise, and higher reliability is achieved.
(6) Multi-function logic valves permit compact integrated hydraulic systems that reduce manifold dimensions and mass and achieve lower cost than that of the conventional types.
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