A hydraulically balanced assembly is provided. The assembly includes: a valve body defining a tapered axial passageway; and a rotor having a tapered outer diameter such that the rotor has a first portion having a wider diameter and a second portion having a smaller diameter, the rotor being dimensioned to fit within the axial passageway of the valve body, the rotor further defining a rotor axial passageway having a first passageway portion and second passageway portion, the rotor further defining a first and second port, where each of the first and second ports provide fluid communication between the tapered outer diameter and the rotor axial passageway, wherein the first and second portions define openings having different cross-sectional areas where the first passageway portion is located in a first portion of the rotor and a second passageway portion is located in the second portion of the rotor and the difference in cross-sectional areas between the first passageway portion and second passageway portion and the amount of taper of the outer diameter of the rotor are related according to the Landrum relation.

A hydraulic port includes: a body defining a first passageway, the first passageway defining a first port at an outer surface of the body; a first thin member located on the body and surrounding the first port, the first thin member being configured to flex away from the first passageway when pressurized fluid flows through the first port.

A hydraulic device having: a plurality of main piston-cylinder arrangements, each of the respective pistons having a fixed stroke length and configured for axial reciprocation within their respective cylinder; a plurality of flow control valves for switching between a lockdown state and an unlocked state of one or more of the plurality of main piston cylinder arrangements during operation of the hydraulic device; and one or more control valves for directing the plurality of flow control valves between their respective unlock and lock positions.

A flow limiter for a cut-off valve of a hydraulic pumping system and a hydraulic system using such a flow limiter. The flow limiter provides for limiting a flow through a cut-off valve. The flow limiter for a cut-off valve of a hydraulic pumping system includes a valve body with a hollow channel. The hollow channel has a fluid inlet and a fluid outlet, and the fluid inlet is in fluid communication with a discharge line of the cut-off valve in a mounted state of the flow limiter. A valve element is slidably arranged within the channel and can transition from a first position towards a second position, if a predefined fluid pressure threshold is exceeded at the fluid inlet. The valve element is arranged in the hollow channel so that in the second position a fluid flow from the fluid inlet to the fluid outlet is larger than in the first position.