The hydraulic high-speed on/off valve (HSV)—the critical core component of digital hydraulic technology—has a special structural design and manufacture due to its fast opening and closing, which results in high prices and maintenance costs. The solenoid screw-in cartridge valve (SCV) is widely used in the hydraulic industry because of its merits, such as mature technology, reliable quality, and low cost. The contribution of this study is to replace the high-speed on/off valve with the SCV in some areas of application by introducing positive and negative pulse voltage control for the coil of the SCV, which only modifies the control circuit and needs no change in structure. Based on the analysis of the structure of the SCV, the simulation model was developed in AMESim and validated by experiments to investigate the effects of the pulse voltage duration on the open–close dynamic characteristics and find the optimal pulse voltage duration, so that the SCV can open or close in the shortest time to reduce energy loss as far as possible. The simulation results showed that the positive and negative pulse voltage could quicken the rising or declining speed of the coil current and dramatically decrease the opening and closing delay time. By the experimental comparison with the original control method, the opening time of the SCV decreased from 30 ms to 13 ms, and the closing time was reduced from 139 ms to 14 ms.

The distribution efficiency of the check valve directly affects the performance of the reciprocating pump. The flow coefficient is an important evaluation criterion for the flow capacity of the valve port, and it is of great significance to the design of the valve structure and even the control of cavitation. The traditional design uses flow coefficient as a fixed value, however, the flow state and flow coefficient will change during valve movement. In this study, a three-dimensional transient computational fluid dynamic model for high-pressure and large-flow reciprocating pump valve is established. The dynamic grid simulation method of coupling for the valves and plunger is innovatively proposed, and experimental verification was carried out. The flow state and pressure characteristics for the suction valve under high outlet pressure are analyzed, and the change rule of the suction coefficient is found. The research results show that the initial pressure of the plunger cavity prolongs the negative pressure duration of the plunger cavity when the valve is opened and increases the risk of cavitation of the valve. During the process from valve opening to maximum lift, the suction coefficient first increases and then decreases, and finally remains between 0.5 and 0.6. When the valve lift is large, two-stage throttling occurs, and the flow state will change from cylindrical jet on the lower surface of the valve disk to annular jet, which is beneficial to improve the suction coefficient.

The end clearance and radial clearance of the gear pump are the most important factors affecting its internal leakage and viscous friction loss, and also the most important factors affecting the total efficiency of a high-speed gear pump. The reasonable value of radial clearance and end clearance is the decisive condition for the high-efficiency performance of high-speed gear pumps. Based on a certain type of high-speed gear pump with a speed of 6000 r/min, the influence of end clearance and radial clearance on internal leakage and viscous friction loss of the gear pump is analyzed under the rated working condition of outlet pressure of 8 MPa. The flow field simulation model of the high-speed gear pump with oil flowing in radial clearance and end clearance is established in PumpLinx. The oil leakage flow rate and pump shaft power under different radial and end clearances are analyzed. The results show that under the condition of 6000 r/min, the phenomenon of insufficient oil filling in the tooth groove is produced, and the radial clearance is 0.16 mm when the total efficiency of the high-speed gear pump is the largest. Under the optimal radial clearance, the working characteristics of gear pumps with different end clearances are analyzed. The end clearance is 0.03 mm when the total efficiency of high-speed gear pumps is the largest. In this paper, the selection of radial and end clearance of high-speed gear pump and the internal flow of different clearances are analyzed, which has important theoretical significance and engineering practical value.

The potential energy recovery of hydraulic excavators is very significant for improving energy efficiency and reducing pollutant emissions. However, the more common solutions for potential energy recovery require more energy conversion processes before these potential energies can be reused, which adds to the complexity and high cost of the system. To tackle the above challenges, we proposed a novel energy recovery system for hydraulic hybrid excavators based on the digital pump with an energy recovery function. The new system could operate in three different modes: pump, energy recovery, and direct reuse. Based on the descriptions of the working principle of the digital pump and the whole energy recovery system, the mathematical models of the digital pump, the excavator arm cylinder, and the accumulator were established and the AMESim simulation model (combining mechanics, hydraulics, and electrics) was developed. The dynamic characteristics of the energy recovery system were studied under no-load and full-load conditions. The simulation results showed that this scheme could achieve 86% energy recovery when the boom was lowered and reused the recovered energy directly when raised, which could decrease the system input energy by 78.1%. This paper can provide an optimized solution for construction machinery or off-road vehicles and presents a reference for the research on digital hydraulics.

Energy storage plays a major role in solving the fluctuation and intermittence problem of wind and the effective use of wind power. The application of the hydraulic accumulator is the most efficient and convenient way to store wind energy in hydraulic wind turbines. A hydraulic energy storage generation system (HESGS) can transform hydraulic energy stored in the hydraulic accumulator into stable and constant electrical energy by controlling the variable motor, regardless of wind changes. The aim of the present study is to design a constant speed control method for the variable motor in the HESGS and investigate the influence of the controller’s main parameters on the resistance of the HESGS to external load power disturbances. Mathematical equations of all components in this system are introduced and an entire system simulation model is built. A double closed-loop control method of the variable motor is presented within this paper, which keeps the motor speed constant for the fixed frequency of electrical power generated by the HESGS. Ultimately, a series of simulations with different proportional gains and integral gains under the environment of changeless load power step are conducted. At the same time, comparison analyses of the experiment and simulation under variable load power step are performed. The results verify the correctness and the usability of the simulation model, and also indicate that the proposed control method is robust to the disturbances of changing load power.

Artificial heart valve replacement is recognized as the most effective method for treating valvular heart disease. Presently, the bileaflet mechanical heart valve is the predominant type utilized. Nonetheless, complications are known to arise following valve replacement surgery, mostly attributable to deviations in the left ventricular blood flow pattern instigated by the dysfunction of the bileaflet mechanical valve. However, the impact of mitral valve leaflet dysfunction on left ventricular hemodynamics has not been studied in depth. Hence, to approximate the physiological conditions of the left ventricular flow and pressure, a left heart circulation pulsatile flow system was devised. The time-resolved particle image velocimetry method was employed to evaluate the left ventricular blood flow under standard working conditions of the bileaflet mechanical valve and in the case where one of the valve leaflets is determined to be functionally impaired. The experimental results reveal that the normally functioning bileaflet valve manifests a tri-jet flow pattern, with intense jets on both sides generating two expansive vortices. Conversely, when one of the valve leaflets is impaired, the tri-jet flow metamorphoses into a bi-jet flow, coupled with augmented velocity. In both instances, the jets traverse along the ventricular model wall and alter their direction subsequent to passing the apex. Consequently, the employment of bileaflet valves culminates in a multifaceted left ventricular blood flow pattern. Furthermore, the valve leaflet dysfunction escalates shear stress, a condition that could potentially instigate damage to blood cells. The insights gained from this study can potentially guide the improved design of the mechanical bivalve.