FAQ

To evaluate the remaining life of a hydraulic system, multiple indicators need to be examined: Oil condition - Use oil analysis to detect changes in viscosity, acid value increase, and contamination to determine the remaining service life of the oil. Wear of key components - Measure the degree of decrease in the volumetric efficiency of the axial piston pump. Generally, if it is less than 80%, overhaul or replacement should be considered. Leakage - If the total leakage of the system exceeds twice that of a new machine, it indicates serious wear. Performance degradation - Compare the current pressure, flow, response speed and other parameters with the differences when the machine was new. Failure frequency - Count the number of failures per unit time. An upward trend indicates that the system has entered a wear and failure period. Economic analysis - Compare the maintenance cost with the replacement benefits. Consider updating when the annual maintenance cost exceeds 30% of the residual value of the equipment. Comprehensive evaluation methods include: regular and comprehensive testing to establish benchmark data; using condition monitoring technology to track key parameters; referring to the average service life of similar equipment; and considering new requirements for equipment due to changes in production processes.

The main reasons why low temperature causes difficulty in starting the hydraulic system are: the viscosity of the oil increases sharply, which increases the oil suction resistance of the axial piston pump and may cause cavitation. The seals harden, the initial friction resistance increases, and especially the cylinder starting pressure increases significantly. The battery capacity decreases and the motor starting torque is insufficient. Countermeasures include: choosing low freezing point hydraulic oil, such as HV or HS series, with a viscosity index higher than 150. Install an oil heater and preheat the oil to above 15°C before starting. Consider installing fuel tank insulation for equipment in cold regions. When starting, run the machine without load for a few minutes to allow the oil to circulate and heat up. Strengthen battery maintenance and use auxiliary starting power when necessary. For extreme environments, consider glycol-water hydraulic systems. For equipment that is out of use for a long time, the oil should be drained and stored, and replaced with new oil before use.

Performance degradation after repair may be caused by the following reasons: Use of non-original or substandard spare parts, such as seals with inappropriate hardness or excessive plunger clearance. Non-standard assembly process, such as bolts not tightened to the required torque or insufficient cleanliness of parts. Failure to address the root cause during repair, such as replacing a damaged axial piston pump without addressing the source of contamination. Inadequate system commissioning, such as improper venting or improper parameter settings. Collateral damage not discovered, such as metal particles from a damaged pump damaging valves. Solutions include: Use original or certified spare parts to ensure quality. Strictly follow the repair manual and use special tools. Thoroughly check the system and address all potential problem points. Thoroughly flush the system and replace all fluids and filters. Fully record the repair process and replaced parts for subsequent tracking.

Hydraulic system failures with multiple symptoms usually have a common root cause: oil contamination may cause axial piston pump wear (increased noise), valve core sticking (abnormal operation) and filter blockage (insufficient flow) at the same time. System air intake will generate noise and reduce the elastic modulus of the oil, resulting in weak actuator action and pressure fluctuations. Excessive oil temperature will accelerate seal aging (increased leakage), reduce viscosity (increased internal leakage), and promote oil oxidation (producing acidic substances). The methods for determining the central fault source include: Time correlation analysis-which symptom appears first may be the root cause. Commonality analysis-find common factors that can explain all abnormalities. Parameter trend-check historical operating data to find the parameters that deviate from normal first. Oil detection-comprehensive oil analysis can reveal a variety of potential problems. For example, the simultaneous occurrence of loud pump noise, high oil temperature and weak cylinder may be caused by excessive internal leakage in the pump, resulting in insufficient flow and energy loss.

Systematic hydraulic fault diagnosis should follow the following steps: Phenomenon observation - record all abnormal performance, such as noise changes, slow movement, pressure fluctuations, etc. Parameter measurement - use pressure gauges, flow meters, etc. to detect key point parameters and compare them with normal values. Gradual isolation - narrow the scope of the fault by operating each control valve or isolating in sections. Sensory inspection - judge abnormal vibration, temperature rise or leakage by listening, touching and watching. Oil analysis - detect oil cleanliness, viscosity, moisture and particle contamination, and judge internal wear. Component exchange - replace suspicious components with normal components to verify the judgment. Fault tree analysis - list all potential causes by probability and eliminate them one by one. Common diagnostic tools include: infrared thermometer to detect abnormal temperature rise, ultrasonic detector to locate internal leakage, and oil quality analyzer to evaluate oil status. Diagnosis should be from simple to complex, first check the oil level, filter element and other easy-to-handle items, and then analyze the internal problems of the components in depth.

The following principles should be followed in designing an efficient hydraulic power unit: Power matching - select the axial piston pump specifications according to the load curve to avoid "a big horse pulling a small cart". Energy efficiency - variable load systems use variable pumps or load-sensitive control to reduce throttling losses. Thermal balance - calculate the system heat generation, ensure heat dissipation capacity, and control the oil temperature within the optimal range of 30-60°C. Noise control - select low-noise pumps, install shock pads, and optimize pipeline layout to reduce turbulence. Reliability - consider redundant design for key systems, such as dual pumps or accumulator backup. Maintenance convenience - set up sufficient detection ports, components are arranged for easy access, and filters have blockage indications. Space efficiency - use integrated valve blocks to reduce piping, compact layout but retain maintenance space. Pollution control - reasonably set up the filtration system, and the oil tank design is conducive to impurity precipitation and gas separation. In addition, the system scalability must be considered, and 10-20% power margin and interface must be reserved.

Accumulators have multiple functions in hydraulic systems: short-term large-volume oil supply to supplement the insufficient flow of axial piston pumps and meet periodic peak demand. Absorb pressure pulsation and reduce pipeline vibration and noise, especially for multi-cylinder pump systems. Emergency energy to provide emergency operating power when the pump fails. Leakage compensation to maintain system pressure stability and reduce frequent pump starts and stops. When selecting an accumulator, consider: Working medium - usually a bladder accumulator is selected, which has good compatibility with mineral oil. Capacity - the required effective volume is calculated according to the purpose, emergency use is calculated according to the actuator action requirements, and pulsation absorption is selected according to 1-2 times the pump single-turn displacement. Pressure - the pre-charge pressure is generally 60-70% of the system's minimum working pressure, and the maximum working pressure does not exceed 90% of the accumulator's rated pressure. Installation location - pulsation absorption should be close to the vibration source, and emergency use should be close to the actuator. In addition, temperature effects, installation space and maintenance convenience need to be considered.

The following factors should be considered when selecting a hydraulic cylinder: Load characteristics - For heavy-duty applications, a reinforced cylinder with a larger piston rod diameter and a longer guide sleeve should be selected. Stroke length - For long strokes (>3m), the stability of the piston rod should be considered. A multi-stage telescopic cylinder or an additional intermediate support can be selected. Installation method - Depending on the force conditions, earring, flange or foot-mounted installation can be selected. Speed requirements - High-speed applications (>0.5m/s) require special buffering design to prevent terminal impact. Environmental conditions - Stainless steel cylinders should be selected for corrosive environments, and special sealing materials should be used for high-temperature environments. Accuracy requirements - Cylinders for machine tools require low friction and high guiding accuracy, and are usually equipped with displacement sensors. Special functional requirements - If intermediate positioning is required, a cylinder with mechanical locking can be selected. If space is limited, a compact cylinder can be selected. In addition, compatibility with existing systems, such as oil port size and working pressure, must also be considered.

Axial piston motors are suitable for the following working conditions: high pressure and high power applications, usually with working pressure of 200-400bar and power of more than 500kW. Applications that require precise speed control or position retention, because of its high volumetric efficiency (up to 95%) and good low-speed stability. Variable speed regulation requirements, wide range of stepless speed change can be achieved by adjusting the displacement. Frequent start-stop or reversing conditions, axial piston motors respond quickly and have small reversing shock. Space-constrained high power density requirements, axial piston motors have a low unit power mass. Long life requirements, the design life can reach more than 10,000 hours. Compared with gear motors, axial piston motors are more efficient but more expensive; compared with vane motors, axial piston motors are resistant to high pressure but are more sensitive to pollution. For low-speed and high-torque requirements, radial piston motors may be more suitable.

Many factors need to be considered when selecting an axial piston pump: First, determine the operating pressure range. For industrial applications, the A4VSO series with a nominal pressure of 350 bar is usually selected, and for mobile machinery, the A10VSO series with a nominal pressure of 250 bar can be selected. The flow demand determines the displacement size. For continuous operation, 70-80% of the rated flow of the pump should be selected as the operating point. In terms of control mode, fixed equipment often uses a constant pressure variable pump (A4VSO DR), and load-sensitive pumps (A10VSO LRDS) are selected for energy saving. When the installation space is limited, consider the through-drive design, and multiple pumps can be connected in series. The ambient temperature affects the selection of oil viscosity, and the low-temperature starting characteristics need to be considered in cold areas. For closed-loop applications such as mobile machinery, select the specially designed A4VSG or A10VZG series. Low-noise designs, such as A2FO metering pumps, should be selected for noise-sensitive occasions. In addition, compatibility with existing equipment, maintenance convenience, and supplier technical support capabilities must also be considered.

A scientific preventive maintenance plan should include the following: Check the oil level, oil temperature, noise and leakage daily, and record abnormal phenomena. Check the filter status, fastener tightness and coupling alignment every month. Check the oil cleanliness and moisture content every quarter, and replace the oil if necessary. Check the bearing status and sealing performance of the axial piston pump and motor every six months, and measure the system pressure and flow. Perform a comprehensive annual disassembly and inspection of key components, such as cylinder seals and valve group internals. Establish benchmark values for key parameters, such as pump noise level and motor starting torque, and predict failures through trend analysis. Use special tools and original spare parts during maintenance, and record the content of each maintenance and the problems found. Adjust the maintenance cycle according to the importance of the equipment, the intensity of use and the environmental conditions, and shorten the interval in harsh environments.

Pressure fluctuations may be caused by the following reasons: Unstable response or improper adjustment of the axial piston pump variable mechanism7. Improper adjustment or spool jam of pressure valves (relief valves, pressure reducing valves, etc.). Air in the system, reduced elastic modulus of the oil. Actuator load changes dramatically, and the system response cannot keep up. Oil contamination causes abnormal valve movement. Ways to stabilize system pressure include: Check and adjust the pump variable mechanism to ensure smooth response. Clean or replace the problem valve to ensure flexible movement of the valve core. Completely remove air from the system and check possible air inlet locations. Install accumulators near the source of fluctuations to absorb pulsations. Improve oil cleanliness and replace filter elements regularly. For systems with drastic load changes, consider using pressure-compensated pumps or load-sensitive controls.