A piston in a liquid-pressure rotating device in which pistons are arranged at a cylinder block rotatable together with a rotating shaft, includes: a cylindrical peripheral wall main body portion including a hollow portion, an opening portion formed at one end of the body portion and communicating with the hollow portion; a lid portion welded to an inner peripheral surface of the opening portion sealing the hollow portion and including an outer surface formed as a pressure receiving surface which receives liquid pressure; and a stress reducing portion provided on an inner peripheral surface of the body portion, the inner peripheral surface in contact with or close to an end portion of a welded portion formed between the opening portion and the lid portion, the end portion located at the hollow portion side, the stress reducing portion configured to reduce stress acting on the end portion of the welded portion.

Systems and methods for a variable displacement hydraulic motor. The hydraulic motor, in one example, includes a swash plate with a tilt angle, multiple piston assemblies configured to rotate about a drive shaft. In the motor, each of the piston assemblies includes an inner piston slideably coupled to an outer piston that mates with a cylinder in a cylinder block and a retainer device configured to inhibit axial movement of the outer piston in a first position and permit axial movement of the outer piston in a second position.

A pump may generally include a frame including a reservoir. The reservoir stores a hydraulic fluid. The pump may also include a motor assembly supported by the frame and a pump assembly operably driven by the motor assembly. The pump assembly is in fluid communication with the reservoir and configured to dispense the hydraulic fluid out of the frame. The pump assembly includes a first piston and a second piston, wherein the first piston dispenses hydraulic fluid out of the frame between a first pressure and a second pressure greater than the first pressure, and the second piston dispenses hydraulic fluid out of the frame between the first pressure and a third pressure, the third pressure being greater than the second pressure.

A hydraulic motor apparatus includes a motor housing engaged to an end cap having a first porting system and an adapter connected to an external surface of the end cap and having a second porting system. A filter may be attached to the adapter and connected to the second porting system and a pressure reducing valve in the adapter is connected to the second porting system. The assembly may also include a controller operatively connected to the pressure reducing valve and system sensors measuring parameters affected by the output of the hydraulic motor apparatus, whereby the pressure reducing valve is operatively controlled by the controller in response to input from the system sensors.

The aim of the invention is to improve the efficiency of an axial-piston motor comprising at least one working cylinder fed by a continuously operating combustion chamber comprising a pre-combustion chamber and a main combustion chamber. To this end, the axial-piston motor is provided with a pre-combustion chamber comprising a check valve.

The aim of the invention is to improve the efficiency of an axial-piston motor comprising at least one working cylinder fed by a continuously operating combustion chamber comprising a pre-combustion chamber and a main combustion chamber. To this end, the axial-piston motor is provided with a pre-combustion chamber comprising a check valve.

An axial piston motor with inner continuous combustion burns a compressed combustion medium with fuel in a continuously operating combustion chamber to form a working medium, the working medium is supplied to cyclical working cylinders in order to extract mechanical energy, and the mechanical energy extracted in the working cylinders is also used for the compression of the combustion medium. The compression is carried out in two steps or at a compression end temperature of less than 300 C. with a compression ratio of more than 10 and/or a rotating distributor includes at least two distributor openings which cyclically open and close the firing connections and/or are cyclically guided past or through firing channels.

A hydraulic axial-piston machine achieves a control cut-off by an additional control edge of a control valve of an actuating mechanism for swiveling a swash plate.

A system for controlling a coiled tubing injector head includes a hydraulic control line in fluid communication with each drive motor, a valve associated with one or both hydraulic control lines, and a sensor associated with each drive motor. Each sensor is configured to output to a digital computer a signal representative of a motor speed, and at least one valve associated with a hydraulic control line is operable to regulate pressure in the hydraulic control line and thereby increase or decrease the speed of the corresponding motor until both speed sensors report substantially matching motor speeds.

A closure element for a fluid end assembly that has two or more recessed grooves formed in its outer surface. The grooves are axially offset. A seal is placed in one and only one of the grooves. As wear occurs, the seal is relocated to one of the other grooves. Instead of a series of axially offset grooves in a single closure element, a kit may be formed from two or more otherwise identical closure elements, each with a single recessed groove at a different axial position. Another closure element has a series of ledge-like surfaces defining spaces within which a seal may be received. One outer surface surrounds one or more of the other surfaces. A seal is placed in one and only one of the spaces. As wear occurs, the seal is relocated to one of the other spaces.