A spool is slidably located in a slide hole of a first housing. A second housing forms a servo chamber that is coaxial with the slide hole. A sleeve is slidably located in the servo chamber. A nut is fixed to a piston that is slidably fitted in the sleeve. An electric motor rotates a screw shaft screwed with the nut. The second housing includes an input port and a drain port. A first pressure chamber communicates with the input port. In a balanced state where forces applied to the sleeve from both sides are balanced, a second pressure chamber is blocked from the input port and the drain port by the piston. From the balanced state, when the piston shifts, the second pressure chamber comes into communication with the input port or the drain port.

A hydraulic system includes a circulation pump assembly (2) provided with a speed controller (4, 26), a hydraulic circuit (A, B) connected to the circulation pump assembly (2) as well as a mechanical switch device (86, 88; 120, 122; 120″, 122″) which is subjected to pressure from a fluid in the hydraulic circuit (A, B) and which can be moved into at least two different switch positions. The mechanical switch device (28; 86, 28; 120, 122) can be moved by the circulation pump assembly (2) by way of a hydraulic coupling via the fluid. The speed controller is configured to initiate a movement of the switch device (86, 88; 120, 122; 120″, 122″) by way of at least one hydraulic force acting thereon and causing a movement of the switch device (86, 88; 120,122; 120″, 122″), produced via the hydraulic circuit, via a speed adaptation of the circulation pump assembly.

An example spool includes a shaft varying in diameter along a length of the shaft, and a plurality of annular lands formed on the shaft and spaced-apart by respective reduced diameter annular neck portions. The plurality of annular lands comprise at least one annular metering land, and wherein the at least one annular metering land comprises: one or more sine notches formed as a portion of a sine wave, and one or more additional notches having a different shape from the one or more sine notches.

A control valve has a housing, which has a first bore in which a control spool is accommodated in such a way as to be movable along a longitudinal axis. The control spool defines first and second orifices which are adjustable. First and second reference planes are each oriented perpendicularly to the longitudinal axis, wherein the first reference plane is defined by a first control edge, more specifically in the position of the control spool in which the first orifice is just closed, wherein the second reference plane is defined by a second control edge, more specifically in the position of the control spool in which the second orifice is just closed. At least one radial recess different from the second bore is provided in the first bore between the first and the second reference plane in the direction of the longitudinal axis.

A servo valve comprises a valve housing, a cavity formed in the valve housing and a member disposed in the cavity and axially-moveable therein. The servo valve further comprises a piezoelectric actuator configured to axially move the member, relative to the valve housing, between first and second axial positions.

A valve may have a fluid inlet and a fluid outlet. The valve may include a valve stem having a lumen extending from a first opening at a proximal portion of the valve stem to a second opening at a distal end of the valve stem. A plurality of seals may be positioned relative to the valve stem. The valve stem and seals may be configured so that a fluid entering the inlet is prevented from flowing to the outlet in a first position of the valve stem and relative to the inlet and the outlet. The valve stem and the seals may be configured so that a fluid entering the inlet flows to the outlet in a second position of the valve stem relative to the inlet and the outlet, the second position being more distal than the first position relative to the inlet and the outlet.

At a preparing stage, a tool is placed in contact with an inner wall of a rotation transmitting portion of an adjustment screw. Then, at an adjustment rotation amount calculating stage, a pre-adjustment oil pressure, which is an output oil pressure of an oil pressure control valve at a pre-adjustment rotational position of the adjustment screw under a predetermined drive condition of a drive device, is sensed, and thereafter an adjustment rotation amount of the adjustment screw from the pre-adjustment rotational position to a target rotational position of the adjustment screw, which corresponds to a target oil pressure, is calculated based on: a differential pressure between the pre-adjustment oil pressure and the target oil pressure; and a correction amount which corresponds to a product characteristic of the oil pressure control valve. Then, at a rotating stage, the adjustment screw is rotated by the adjustment rotation amount.

An end of a first land has a step difference recessing inward of a radial direction of the first land from the edge portion. The step difference has an end point opposite to the edge portion. A throttle portion protrudes from the start point in an axial direction, and includes an outer-peripheral corner (protrusion round portion) having a curved surface protruding in the axial direction and in the radial direction. When an inlet opening starts to be slightly opened, since a hydraulic fluid is throttled when flowing through a second gate opened between a corner of a sleeve and the protrusion round portion, a rapid increasing of a flow quantity of the hydraulic fluid and an instability of a control of the hydraulic fluid can be suppressed.

A first flow path area at a position where one of multiple openings of a sleeve and one of multiple grooves of a spool overlap with each other is different in size from a second flow path area at a position where another one of the openings of the sleeve and another one of the grooves of the spool overlap with each other. The one opening and the one groove form a flow path for connecting one of one pressure chamber and the other pressure chamber to a fluid supply source, due to displacement of the spool. The other opening and the other groove form a flow path for connecting another one of the other pressure chamber and the one pressure chamber to a fluid discharge port, due to the displacement of the spool.

A valve assembly includes a valve housing having a first port, a second port, and a third port. A valve member within the valve housing is moveable therein to alter fluid communication between the first and second ports. The valve housing includes a first annular groove such that a first sealing ring is provided in the first annular groove, thereby sealing the first port from the second port when installed in a receiving bore. The valve housing also includes a second annular groove such that a second sealing ring is provided in the second annular groove, thereby sealing the second port from the third port in the receiving bore. The valve housing also includes a first anti-tip flange extending radially outward to a greater extent than the first annular groove and a second anti-tip flange extending radially outward to a greater extent than the second annular groove.