A pressure-limiting valve with feed function, comprising a valve housing (20) having at least two connection points, in particular in the form of a working connection (A) and a tank connection (T), and having a spring-loaded pressure-limiting valve piston (22) which is mounted such as to be longitudinally movable in the valve housing (20), and having a spring-loaded non-return valve piston (56) for the implementation of the feed function, is characterized in that the non-return valve piston (56) is designed as a hollow piston and is mounted such as to be longitudinally movable in the valve housing (20).

A work machine includes: a hydraulic actuator; a closed-circuit pump that is connected to the hydraulic actuator in a closed circuit, and supplies and discharges a hydraulic working fluid to and from the hydraulic actuator; an open-circuit pump that is connected to the hydraulic actuator in an open circuit, and supplies the hydraulic working fluid to the hydraulic actuator; a charge pump; a charge flow path that introduces the hydraulic working fluid delivered from the charge pump to the closed circuit; an excess fluid discharging device that discharges an excess hydraulic working fluid of the closed circuit to the charge flow path; and a controller that controls a delivery capacity of the closed-circuit pump and a delivery capacity of the open-circuit pump. The controller increases the delivery capacity of the open-circuit pump, or reduces the delivery capacity of the closed-circuit pump when a state of a pressure of the charge flow path has transited to be lower than a predetermined pressure threshold from equal to or higher than the predetermined pressure threshold, or when a state of the work device has transited to a state of performing the excavation work from a state of not-performing the excavation work.

A void protection system includes a valve assembly, a second fluid source configured to provide hydraulic fluid to the hydraulic cylinder, an auxiliary valve configured to fluidly connect the hydraulic cylinder to the second fluid source, a sensor assembly, and a controller. The controller is configured to monitor fluid pressure within the hydraulic cylinder based on signals from the sensor assembly, based on a determination that pressure in a rod end or a head end of the hydraulic cylinder is below a first fluid pressure threshold, configure the valve assembly to fluidly connect the corresponding end to the first fluid source, and if the first fluid source is not operational, increase an opening of the auxiliary valve to fluidly connect the corresponding end to the second fluid source and cause the second fluid source to provide fluid until pressure in the corresponding end is above a second fluid pressure threshold.

A device for cavitation detection of a pure water hydraulic system based on pressure includes a chamber component; an inner diameter of the drainage nozzle gradually increases along an inflow direction of a liquid medium, so as to reduce a flow velocity of the liquid medium after being drained into the drainage nozzle; and the detection assembly includes a housing, one end of the housing facing the drainage nozzle is an open end, an elastic cover sheet is arranged in the open end, an electrode is arranged in the housing, diaphragms are respectively arranged on two sides of the electrode, and the electrode is closely attached to the elastic cover sheet through one of the diaphragms; the liquid medium is ejected from the drainage nozzle and impacts the elastic cover sheet.

A device for cavitation detection of a pure water hydraulic system based on pressure includes a chamber component; an inner diameter of the drainage nozzle gradually increases along an inflow direction of a liquid medium, so as to reduce a flow velocity of the liquid medium after being drained into the drainage nozzle; and the detection assembly includes a housing, one end of the housing facing the drainage nozzle is an open end, an elastic cover sheet is arranged in the open end, an electrode is arranged in the housing, diaphragms are respectively arranged on two sides of the electrode, and the electrode is closely attached to the elastic cover sheet through one of the diaphragms; the liquid medium is ejected from the drainage nozzle and impacts the elastic cover sheet.

A work machine includes: a hydraulic actuator; a closed-circuit pump that is connected to the hydraulic actuator in a closed circuit, and supplies and discharges a hydraulic working fluid to and from the hydraulic actuator; an open-circuit pump that is connected to the hydraulic actuator in an open circuit, and supplies the hydraulic working fluid to the hydraulic actuator; a charge pump; a charge flow path that introduces the hydraulic working fluid delivered from the charge pump to the closed circuit; an excess fluid discharging device that discharges an excess hydraulic working fluid of the closed circuit to the charge flow path; and a controller that controls a delivery capacity of the closed-circuit pump and a delivery capacity of the open-circuit pump. The controller increases the delivery capacity of the open-circuit pump, or reduces the delivery capacity of the closed-circuit pump when a state of a pressure of the charge flow path has transited to be lower than a predetermined pressure threshold from equal to or higher than the predetermined pressure threshold, or when a state of the work device has transited to a state of performing the excavation work from a state of not-performing the excavation work.

The valve module can be installed regardless of an oil level, for example of an oil level of an oil sump of a motor vehicle. By means of a buffer volume having an overflow it is always guaranteed that a leakage flow conveyed past a valve piston includes no air but consists solely of hydraulic medium, since the overflow guarantees a level of hydraulic medium which lies above an upper face of the valve piston in a preferred installation position. As a result, foaming of the hydraulic medium can be prevented. The valve module can also be installed above the oil sump, for example in an upper region of a gearbox of the motor vehicle. In addition, the oil from the overflow can be used for cooling/lubrication of further drive train components.

The valve module can be installed regardless of an oil level, for example of an oil level of an oil sump of a motor vehicle. By means of a buffer volume having an overflow it is always guaranteed that a leakage flow conveyed past a valve piston includes no air but consists solely of hydraulic medium, since the overflow guarantees a level of hydraulic medium which lies above an upper face of the valve piston in a preferred installation position. As a result, foaming of the hydraulic medium can be prevented. The valve module can also be installed above the oil sump, for example in an upper region of a gearbox of the motor vehicle. In addition, the oil from the overflow can be used for cooling/lubrication of further drive train components.

A hydraulic system includes: a first bi-directional pump connected to a head-side chamber of a single-rod cylinder by a head-side line and connected to a rod-side chamber of the single-rod cylinder by a rod-side line; and a second bi-directional pump connected to the head-side line by a supply/discharge line, the second bi-directional pump being a variable displacement pump. The hydraulic system further includes a low-pressure selection valve connected to the head-side line by a first discharge line and connected to the rod-side line by a second discharge line, wherein the low-pressure selection valve allows the second discharge line or the first discharge line to communicate with a relief line on which a relief valve is located.

A crane, in particular a mobile crane, having a closed hydraulic circuit in which a hydraulic pump is hydraulically connected to at least one hydraulic motor via a feed and a discharge, and in which the feed is hydraulically connected to the discharge via at least one bypass which bypasses the at least one hydraulic motor, wherein the at least one bypass includes a continuously adjustable valve for variably controlling the fluid flow bypassing the at least one hydraulic motor. In addition, a corresponding control device and a corresponding crane control program for actuating a closed hydraulic circuit of a crane are provided.