A hydraulic system that has a hydraulic pump connected to and in communication with a hydraulic motor, at least one hydraulic cylinder, or both by a first conduit and a second conduit (i.e., a high side and a low side). The hydraulic system has a bypass valve connected to and in communication with the first conduit and the second conduit. The bypass valve has a preset pressure that is above a minimum low side pressure. When a shock load occurs in the hydraulic system and a related drop in pressure on the low side occurs, the bypass valve opens when the preset pressure is passed thereby preventing the pressure from dropping to the minimum low side pressure. The hydraulic system thereby avoids a low loop event that could cause damage to the hydraulic system without the presence of larger charge pumps or accumulators.

A high pressure plunger pump, having at least one plunger arrangement which comprises a working space connected to a valve seat suction line and a valve seat pressure line, in which a plunger is arranged in an axially reciprocable manner, wherein the valve seat pressure line is closeable by a pressure valve and the valve seat suction line by a suction valve, and the suction valve can be kept in an open position in a controlled manner as required by means of a counter-pressure device, is designed so that the counter-pressure device has a supply line via which a control fluid can be guided to the suction valve for keeping the suction valve open, wherein a low-pressure pump is connected to the supply line for generating pressure of the control fluid.

A system includes a variable displacement pump (VDP) in fluid communication with an inlet line and with an outlet line. The VDP includes a variable displacement mechanism configured to vary pressure to the outlet line. A relief valve (RV) includes an RV inlet in fluid communication with the outlet line, and an RV outlet in fluid communication with a bypass line that feeds into the inlet line upstream of the VDP. An actuator is operatively connected to control the RV to change function of the RV between a first function and a second function. The first function is a high pressure relief valve function. The second function is as a wind milling bypass function. A controller is operatively connected to the actuator to control the RV to change back and forth between the first function and the second function.

A system includes a variable displacement pump (VDP) in fluid communication with an inlet line and with an outlet line. The VDP includes a variable displacement mechanism configured to vary pressure to the outlet line. A relief valve (RV) includes an RV inlet in fluid communication with the outlet line, and an RV outlet in fluid communication with a bypass line that feeds into the inlet line upstream of the VDP. An actuator is operatively connected to control the RV to change function of the RV between a first function and a second function. The first function is a high pressure relief valve function. The second function is as a wind milling bypass function. A controller is operatively connected to the actuator to control the RV to change back and forth between the first function and the second function.