On January 8, 2025, Professor KONG Xiangdong from Yanshan University was invited to give a presentation titled “Conservation and Breakthrough Integration of Technological and Industrial Innovation Advancing Hydraulic Components and Systems Toward High-end, Intelligent, and Green Development” at the “2025 Welcome Spring Festival Seminar of China Hydraulics Pneumatics & Seals Association” held in Beijing. Professor KONG Xiangdong analyzed the development advantages, bottlenecks, and prospects of hydraulics pneumatics & seals industry in the transformation towards high-end, intelligent, and green (three modernizations). Starting from the theoretical core of “Conservation and Breakthrough” and “Integration of Technological and Industrial Innovation”, he emphasized that the industry needs to consolidate the foundation of theory and process inheritance with “Conservation”, promote high-level technological self-reliance and self-improvement in the field of hydraulics pneumatics & seals with “Breakthrough”, and drive the high-end, intelligent, and green development of hydraulics pneumatics & seals industry through “Integration of Technological and Industrial Innovation”. The report also combines the exploration and practice of the hydraulic major and its research team at Yanshan University on the path of “Three Modernizations” development, and introduces a series of practical measures such as talent cultivation, diversified integration development, and technological innovation and transformation of the research team in the hydraulic engineering major at Yanshan University, to help solve the “Three Modernizations” development problems in hydraulics pneumatics & seals industry. This article is compiled from on-site reports and provides a theoretical framework and practical inspiration for the development of the “Three Modernizations” in hydraulics pneumatics & seals industry.

The wave compensation system of offshore trestle can realize the safe and efficient transfer of personnel and materials at sea, and is the key system of large marine operation and maintenance ships. Aiming at the bottleneck problem of high energy consumption in the wave compensation system of offshore trestle, a design scheme of active- passive composite wave compensation electro-hydraulic system for pitching joint of offshore trestle is proposed in this paper. Firstly, this paper analyzes the mechanical structure of the wave compensation system and its working principle of the pitching joint. A passive wave compensation system based on high-pressure gas follow-up support is designed to reduce the energy consumption caused by gravity during the pitching action of offshore trestle. An active wave compensation hydraulic control system based on electro-hydraulic valve group is designed to realize the closed-loop control of pitching motion of offshore trestle. Then, through theoretical modeling and simulation analysis, the mechanism of the designed system to compensate the trestle's dead load is revealed, the energy distribution of the passive compensation system and the active compensation system is analyzed, and the energy consumption characteristics of the designed active-passive composite wave compensation electro-hydraulic system under different passive compensation pressures are explored. Finally, the active-passive composite wave compensation electro-hydraulic system for pitching joint of offshore trestle is developed, and the driving and control capability of the designed system is verified by experiments. The results show that the designed active-passive composite wave compensation electro-hydraulic system can realize the low energy consumption and high precision control of the offshore trestle, which has important strategic significance for the future installation, operation and maintenance of offshore wind power in China.

The unique structural design of the three-anchor buoy system can further improve the observation ability, stability and working reliability, avoid the entanglement of underwater equipment and anchor chain, and help to realize the monitoring of marine water profile data, which plays an important role in the field of marine monitoring. To explore the static characteristics of a single anchor chain within a moored buoy system under shallow sea conditions and the effects of buoy offset on the tension in each anchor chain and the system's restoring force. Based on the catenary equation considering the ground chain, the static characteristics of a single anchor chain are solved according to the Newton-Raphson iteration method. Through the static analysis of the three-anchor buoy mooring system, the effects of different offset displacements and offset angles on the tension of each anchor chain, the length of the catenary in the water, the system restoring force and its direction angle are investigated. The results show that the stiffness of the anchor chain increases with the increase of the horizontal span of the catenary. When the offset angle is constant, the restoring force of the buoy system increases with the increase of the offset displacement of the buoy. When the offset displacement is constant, the recovery force of the buoy system increases first and then decreases with the increase of the offset angle.

The rotor needs to bear a huge inertial force during the rotation process, which requires high assembly quality and thus affects the selection of the number of measurement points during rotation. In this regard, a study on the selection of the number of predicted measurement points for rotor assembly under stacking optimization is proposed. Based on historical data of rotor assembly, using stacking optimization technology, a rigid stacking model is established, and the physical characteristic equation of rotor assembly is designed. A rotor assembly accuracy prediction model is established to screen out the number of predicted measurement points with high assembly accuracy. Based on this, with the goals of minimizing assembly errors, maximizing assembly accuracy, and minimizing measurement costs, the objective function and constraints are set. By calculating the sensitivity of different numbers of measurement points, the optimal number of measurement points for assembly effect can be determined. The experimental results show that the designed selection algorithm has good performance in practical applications with an eccentricity of 0.85 mm.

Electro-hydraulic servo valve is the core control element in high-precision deep-sea hydraulic equipment, and its performance and reliability are the key factors to determine the control accuracy and reliability of deep-sea hydraulic system. Under the extreme working conditions of the deep sea, the tiny deformation of the valve spool and the valve sleeve affects the control performance of the electro-hydraulic servo valve. This paper establishes a three-dimensional model of the double-nozzle baffle valve, and based on the environmental conditions of the variable depth of the sea, it studies and analyzes the deformation law and internal leakage of the slide valve under different depths of the sea. The results show that when the sea depth is 12 000 m, the gap between the spool and the valve sleeve is reduced to 2.752 μm, and the leakage is reduced to 0.020 5 L/min, which is close to 50% of the deformation and 98% of the leakage compared with the land environment. The results can be used to predict the use of electro-hydraulic servo valves in deep-sea environments, and this study is of great significance to the research of hydraulic systems.

In centrifugal pumps and other rotating machinery, the mouth ring is usually used as a part to reduce the leakage flow, but with the decrease of the mouth ring clearance and the increase of the rotor speed, the influence of the rotor dynamic characteristics on the safe operation of high-speed pumps cannot be ignored. Based on the numerical simulation method, the stiffness damping characteristics of the mouth ring of a high speed centrifugal pump under working condition are calculated and studied in this paper. By modeling the flow field of a high speed centrifugal pump, the stiffness damping characteristics of the rotor in the mouth ring with different eccentricities and deviation angles are calculated. The results show that the stiffness damping characteristics of the mouth ring clearance are nonlinear related to the rotor eccentricity. The influence of inlet pressure distribution on stiffness damping of rotor under different eccentricity and deviation Angle is obvious. The circumferential asymmetry of inlet pressure causes the circumferential asymmetry of stiffness damping characteristics of mouth ring, in which the influence of main stiffness is most obvious.

Digital twin can build a digital model in the virtual space that is similar in shape and behavior to the physical entity, which is an advanced technology to realize the fusion of virtual and real. The performance of relay valve directly affects the safe operation of EMU, so it is of great significance to study its behavior state under health and fault conditions. Based on the digital twin modeling technology and basic mathematical model principle, this paper constructs the digital twin model of relay valve, and corrects the digital model under health condition through genetic algorithm to improve the accuracy of the digital twin model of relay valve. By injecting common faults into the relay valve health model and simulating the working state of the relay valve under fault conditions, the digital twin model of the trunk valve is accurately mapped to the physical entity.

To investigate the effect of dynamic and static pressure combined mechanical seal on liquid film cavitation, a three-dimensional liquid film model was established using the Rayleigh step ring groove static pressure step as the research object. A comparative analysis was conducted on the cavitation area and leakage rate of the Rayleigh step ring groove and Rayleigh step ring groove static pressure step models, revealing the sealing mechanism of the Rayleigh step ring groove static pressure step fluid dynamic and static pressure combined mechanical seal. The research results show that the cavitation area of Rayleigh step ring groove static pressure step is larger than that of Rayleigh step ring groove, and the former has a smaller leakage rate. The cavitation area extends from the root of the reverse groove to the groove area, and the ratio of cavitation area and gas phase volume fraction increase with the increase of rotational speed, but decrease with the increase of pressure and film thickness. Therefore, under high pressure conditions, the forward and backward Rayleigh step ring groove static pressure step fluid dynamic and static pressure combined mechanical seal can better reduce leakage.

The vibration signal of hydraulic rolling bearing of coal preparation crusher is affected by environmental noise, which presents periodic impact and nonlinear energy characteristics, which makes the fault identification result inaccurate. Therefore, an IMF method for fault vibration identification of hydraulic rolling bearing of coal preparation crusher based on periodic impact is proposed. Through Empirical Mode Decomposition (EMD) technology, the vibration signal collected by the three-axis acceleration sensor is decomposed into the Intrinsic Mode Function (IMF), and the abnormal energy moment features in the IMF are extracted. The cuckoo optimization algorithm is used to improve the clustering effect of the peak density clustering algorithm, and the local density value of the IMF energy moment characteristic is calculated to recognize the fault vibration of the hydraulic rolling bearing of the coal separation crusher. The experimental results show that the proposed method can effectively identify the fault vibration of hydraulic rolling bearings under different fault conditions, and the identification results are consistent with the actual situation, indicating that the method has a good recognition accuracy.

To ensure that the hydraulic damping device of the stepper machine can maintain good stability and reliability under different operating conditions, dynamic response of the damping force, the internal friction characteristics, and return characteristics of the hydraulic damping device were tested and analyzed based on the WPW-30A comprehensive test stand. According to the composition and working principle of the hydraulic damping device, the excitation loading scheme was established. The variation laws of the damping force with respect to speed, stroke, and temperature were obtained through parameter setting. The friction response was tested under low-speed conditions to avoid the interference factors of the damping force. The variation laws of the residual displacement under different excitation frequencies and different limit stroke conditions were obtained. The research results show that the comprehensive mechanical properties of the hydraulic damping device are good. The fluctuation value of the friction force during the reciprocating stroke is less than 5%, the minimum return rate under the limit conditions is more than 85%, and the hysteresis problem under high-frequency excitation is not significant. The dynamic performance testing method can provide effective design ideas and technical solutions for the development of hydraulic damping devices.

In order to elucidate the influence of axial preload on the sealing characteristics of plunger pump packings, three distinct axial preload schemes—1300.4, 780.3, 260.1 N were devised for theoretical investigation. The finite element method was used to simulate and analyze the axial distribution of the contact stress and equivalent stress in the sealing pair, and the findings were subsequently verified through experiments. The results show a strong positive correlation between the axial preload and both the contact stress of the sealing pair and the equivalent sealing stress of the packing. An increase in preload causes the contact stress near the sealing end to exceed the sealing pressure, which in turn hinders effective lubrication and cooling of the sealing pair, thus compromising the long-term operation of the packing. There exists an optimal preload at which the contact stress at the sealing end is equal to the sealing pressure, thereby ensuring both excellent sealing performance and extended service life. Comparative testing of the sealing pair's contact stress at different axial positions, along with macroscopic leakage experiments, confirmed the accuracy of the design approach. These findings offer valuable guidance for the design and application of reciprocating seals.

This article introduces the structure and working principle of a fixed value pressure reducing valve used in a certain type of axial piston variable displacement motor, and theoretically calculates its structural parameters. The static and dynamic characteristics of the constant pressure reducing valve were analyzed, and a simulation model of the constant pressure reducing valve was built using AMESim software. The influence of the damping equivalent diameter of the constant pressure reducing valve on the pressure building process, delay time, and start stop process of the Br chamber was specifically discussed, and experimental verification was carried out, providing theoretical guidance for the subsequent design improvement and mass production of the constant pressure reducing valve.

In this paper, the effect of mineral oil content on the foam resistance of phosphate ester was studied. It was found that a very small amount of hydrocarbon oil (<0.1%) would lead to a significant increase in the foam resistance of fuel oil. The mineral oil content of two kinds of phosphate ester resistant fuels used in two power plants of CGN was determined by DL/T 1979—2019 method. The composition of the obtained mineral oil was detected by GC-MS. The results showed that the oil soluble substances (mineral oil) obtained after the new oil test were not completely hydrolyzed phosphate ester resistant fuel, partial hydrolyzed products and additives such as silicone oil. The oil soluble substance (mineral oil) obtained after the test of the old oil includes the incomplete hydrolyzed phosphate ester resistant fuel and some hydrolyzed products, as well as some high-boiling substances, which may be hydrocarbon mineral oil or the saponification of the hydrolyzed products and metal ions in the old oil. Therefore, the power plant should optimize the saponification and extraction methods when detecting the mineral oil content in the resistant fuel oil, to ensure that the resistant fuel oil is completely hydrolyzed during the test process, and to avoid the influence of hydrolytic products on the test results.

In this paper, the finite element model of metal C-type seal ring is established through the finite element analysis software ABAQUS, and the main influencing factors and variation rules of compression recovery performance of C-type seal ring are obtained, which are compared with the test results. The effects of alloy layer thickness, opening size, material and temperature on the mechanical properties of metal C-type seal ring were studied, and the suitable deformation range, contact width and contact stress were obtained. The mechanical properties of metal C-type seal ring under self tightening and non self tightening installation modes are studied. It shows that self tightening installation has better mechanical properties, while non self tightening installation has little effect on mechanical properties.

The drag parachute was an important equipment for aircraft to land safely using resistance parachutes in emergency situations. This paper mainly discussed on a typical fault of the drag parachute of a certain type of aircraft. The fault tree analysis(FTA)method was used to analyze and diagnose the fault based on the working principle diagram. A fault tree and fault structure function were established with the fault phenomenon as the top event, and all basic events corresponding to the fault were obtained. Combined with the prior probability of the basic event of such faults calculated by a certain unit, the failure probability of the fault phenomenon was obtained through importance calculation. And the diagnostic mainstream and fault isolation method for this fault were formulated. It can provide a basis and reference for the efficient diagnosis and daily maintenance of this type of aircraft.

Hydraulic cylinder is the most important actuator in hydraulic systems. This article proposes a mechanical self-locking hydraulic cylinder based on the pre tightening force of the disc spring. This hydraulic cylinder can accurately lock the piston rod in any position for a long time, meeting certain high positioning accuracy requirements in certain usage scenarios. This article first establishes a calculation model for the piston rod locking theory, designs a three-dimensional model of the locking mechanism, and uses the three-dimensional model to conduct ANSYS transient structural simulation. Finally, a prototype of a mechanical self-locking hydraulic cylinder was made based on theoretical calculation results and a three-dimensional model. Simulation and experimental results show that the model can achieve precise long-term locking of the hydraulic cylinder piston rod at any position.

Aiming at the impact and noise generated in the working process of the hydraulic check valve automatic oil filling and pressure retaining circuit, the AMESim simulation model of the automatic oil filling and pressure retaining circuit with pressure relief function is established. Through comparison and analysis with the original scheme, it is found that the pressure relief mode can achieve more stable pressure relief by setting a unidirectional throttle valve on the oil circuit of the piston rod up and back, so as to avoid large hydraulic shock and noise.