The subject matter of this specification can be embodied in, among other things, a check valve that includes a valve body having a bore and a seat along the bore, a fluid inlet at a first end of the bore, and a fluid outlet a second end of the bore, a stopper selectively movable along the bore to contact the seat, the bore being occluded when the stopper is in contact with the seat, a first bias member on a first side of the stopper within the bore, the first bias member providing a first bias force upon the stopper in a first direction, and a second bias member on a second side of the stopper within the bore, the second side being opposite the first side, the second bias member providing a second bias force upon the stopper in a second direction opposite the first direction.

Hydraulic fluid release valve assemblies are described herein. The hydraulic fluid release valve assemblies may include a hydraulic unit base with a hydraulic fluid return channel and a hydraulic fluid release valve that is at least partially inserted in the hydraulic fluid return channel. The hydraulic fluid release valve assembly may further include a driving assembly to contact with the hydraulic fluid release valve to apply a pushing force on the hydraulic release valve to open the hydraulic fluid release valve, and an electrically powered driver connected to the driving assembly, the electrically powered driver, when actuated, causes the driving assembly to move to apply the pushing force to the hydraulic fluid release valve.

A pressure relief valve includes a valve body having an inner wall defining a cylindrical bore. The inner wall includes a threaded region having a plurality of threads. The valve includes a pressure control calibration spring including a calibration portion and a force application portion. The calibration portion is threaded into the threads of the threaded region. The valve body includes an aperture in fluid communication with the cylindrical bore. An inner perimeter of the aperture defines a valve seat. A valve member is receivable on the valve seat. The force application portion urges the valve member into engagement with the valve seat and has a pitch that is greater than a pitch of the calibration portion. Rotation of the calibration portion in the threads of the threaded region of the valve body adjusts the spring force applied to the valve member by the force application portion.

Hydraulic fluid release valve assemblies are described herein. The hydraulic fluid release valve assemblies may include a hydraulic unit base with a hydraulic fluid return channel and a hydraulic fluid release valve that is at least partially inserted in the hydraulic fluid return channel. The hydraulic fluid release valve assembly may further include a driving assembly to contact with the hydraulic fluid release valve to apply a pushing force on the hydraulic release valve to open the hydraulic fluid release valve, and an electrically powered driver connected to the driving assembly, the electrically powered driver, when actuated, causes the driving assembly to move to apply the pushing force to the hydraulic fluid release valve.