The hydraulic oil in the electro-hydraulic actuators should be replaced regularly, about every 2000 – 4000 hours of operation. Also, check the integrity of pipeline seals and control circuits. The gear clearance must be within the range of 0.1 ~ 0.2 mm, and lubrication must be done once every approximately 1000 hours of work. The machine is supposed to stop cooling if the temperature rises beyond 60 degrees Celsius.
Maintenance of the Transmission System
The transmission system is one of the most important components in an actuator to ensure a stable and precise operation. Maintaining this system requires attention to a number of aspects with the objective of avoiding loss of accuracy or insufficient power due to wear. A too-large gear clearance would reduce efficiency and result in operational deviation. Industry standards generally recommend an inspection every six months should be certain the gear clearance remains within the optimal range for most electrohydraulic equipment 0.1 to 0.2 mm.
The Vibration in the transmission system usually indicates that some parts could be loose or worn. Most of the companies in the industry use precision vibration sensors to detect the smoothness of the transmission system, and these vibration sensors provide zero-error vibration value references. Normally, a higher vibration value over 2 mm/s indicates immediate maintenance needs; otherwise, it would result in higher maintenance costs.
It is also very important to carry out daily monitoring of the temperature of the transmission shaft. Too high of a temperature accelerates the wearing of gears and bearings. Most of the normal operating temperatures of electro-hydraulic actuators range from 60-70 degrees centigrade. If it is too high, stop using the machine immediately and conduct an inspection. Each additional 10-degree centigrade cuts by half the service life of gear oil. Therefore, the frequency of replacing the oil should be increased if the temperature goes beyond the permissible range to avoid oxidation or degradation in the performance of the grease with high temperatures.
Checking Pipeline Seals
Sealing is indispensable for good functionality-performance of the electrohydraulic actuators; each leakage or spillover of the oil reduces the efficiency of the device and can even develop serious safety hazards. Up to 15% power loss may be caused by leakage in hydraulic equipment, which badly raises the operating costs over long periods. Each joint, seal ring, and valve is a critical point in pipeline sealing. Any problem at these places affects the system’s overall seal integrity.
Most of the manufacturers recommend a detailed pipeline seal inspection every quarter, especially in high-load or high-pressure working conditions. Generally, in such working conditions, after 4000 hours of operation, seals exhibit considerable wear. Hence, it is normal industry practice to inspect the seal rings and gaskets every 1000 hours of operation to avoid hydraulic oil loss and entry of contaminants into the system to maintain hydraulic oil purity.
The condition of the stable and no leakage under the high pressure reflects good sealing performance. During tests, most of the electro-hydraulic actuators are under the pressure test at about 80 to 90 bar. All the pressure drops or oil leakage have to be replaced for their corresponding seal components immediately. If the bad sealing leaks were ignored, it could be as high as $500 in repair costs, and frequent occurrences could lead to a phenomenal increase in annual expenditure.
Inspecting Control Circuits
Control circuits are a big part of an actuator since they directly affect the precision and quick response of the device. In reality, about 40% of failures of an electro-hydraulic actuator come from control circuit failures; any fault in wiring may lead to machine failure or malfunction. The integrity and stability of every circuit become especially crucial in a high-frequency use environment. In general, the industry recommends checking the whole circuit every six months to make the wiring and port connections stable, hence reducing failure rates during operation. Checking the tightness of the terminal connections regularly can avoid situations like a short circuit and bad contact, especially under high loads.
Loose connections may reduce power output by 5-10%, which will affect the precision control of the electrohydraulic actuator. In this way, the insulation layer of the continuously operating circuit is aging, and the possibility of a short circuit is increased. It is necessary to keep the insulation resistance of the control circuit above 1 MΩ to prevent current leakage effectively. Applying high-temperature-resistance insulating materials in the circuits is conducive to raising the aging resistance. Although this kind of line is more expensive, it extends the operating cycle under harsh conditions.
Monitoring the temperature and load conditions of the circuit can determine in advance the emergence of various hazards. Normally, when the temperature of the circuit exceeds the design temperature, which is between 50 to 60 degrees Celsius, the insulation material may gradually lose its protective function. In particular, if the operating condition is continuous 24 hours per day, the temperature and load data can be monitored to determine the health status of the circuit. For every increase of 10 degrees Celsius in the temperature of the circuit, the lifespan is halved; therefore, most companies equip an electro-hydraulic actuator with a temperature control alarm system. Once the temperature exceeds the threshold, the system will immediately come to a stop to avoid high temperatures affecting the lifespan of the device.
Hydraulic Oil Replacement Cycle
Hydraulic oil is the lifeline in the operation of the electro-hydraulic actuator, determining device performance and service life. The hydraulic oil replacement cycle is about 2000 to 4000 hours, depending on the workload and environmental conditions. If hydraulic oil deteriorates, the system power output will decrease, and equipment wear will increase. Companies usually set a 2000-hour replacement interval as the standard cycle to maintain the best condition for a device.
In hydraulic oil replacement determination, it is important to monitor oil viscosity and TAN. Hydraulic oil becomes more oxidant and impurities as it ages. The acid value rises and increases the possibility of corrosion. In hydraulic oil, the acid value should not be more than 0.5 mg KOH/g. Once this value is surpassed, oil replacement must be carried out. In a high-temperature and high-load working condition, the hydraulic oil worsens faster. Thus, the status of the oil needs to be checked every 1,500 hours so that the viscosity remains within a reasonable range.
According to the different working conditions, the frequency of hydraulic oil replacement also differs. For example, in a highly polluted working environment, the amount of impurities in hydraulic oil increases rapidly, which blocks the filters and eventually decreases the performance of the hydraulic oil. In highly polluted conditions, the hydraulic oil replacement cycle is usually shortened to 1000 hours, while machinery running in clean rooms can extend the replacement cycle even to 4000 hours. A high-performance filtration system means a great deal to prolong the service life of hydraulic oil and keep the hydraulic oil circuit clean. As recommended, every 500 hours, the filter shall be cleaned or replaced with a new one, if necessary, so as to maintain the purity of hydraulic oil.
