Hydraulic gear pumps are widely used in hydraulic drive systems due to their high pressure capability, resistance to contamination, and cost-effectiveness. They are commonly found in construction machinery and various industrial applications. However, during the factory trial runs, a phenomenon known as "brooming" occurs, which generates pollutants. These contaminants can directly pollute the hydraulic test system. Due to limitations in current oil pollution control technologies, the remaining oil inside the pump can also lead to internal contamination, reducing the reliability of the hydraulic system. As a result, research into oil purification technology for gear pump test stands has gained significant attention across the industry. According to industry standards, the oil contamination level on a gear pump test stand should not exceed ISO 4406-19/16, equivalent to NAS 1638-10. In 2006, we selected Shandong Runuang Hydraulic Technology Co., Ltd. (now Haldex (Qingzhou) Co., Ltd.), a large and representative company in the gear pump industry, as a test site. Oil samples were collected, analyzed, and tracked over time. The results showed that the oil cleanliness was at NAS 1638-13, indicating a serious contamination level. More than 80% of the particles were in the 10–30 μm range, mainly due to the brooming effect caused by conventional filters. Since the pump body is mostly made of aluminum alloys, these particles remain suspended in the oil. As the number of tests increases and time passes, the oil's cleanliness deteriorates, leading to a sharp decline in its physical properties and poor test results. Residual oil in the pump also poses hidden risks for future use. Previously, the company relied on frequent oil replacements and secondary cleaning after each test, which resulted in significant waste of resources. This oil pollution issue became a major challenge for the company and attracted widespread attention in the industry. Through analysis and comparison, we concluded that due to the design of the gear pump, the brooming phenomenon during testing is unavoidable. To address this, it’s essential to implement effective cleaning equipment within the test system. The purification equipment must have a high dirt capacity and filtration accuracy. Based on this, we recommended introducing the German KLEENOIL ultrafiltration device next to the oil tank. The device uses long polypropylene fibers as filter media, offering excellent particle retention and dehydration capabilities. It can effectively remove fine particles above 1 μm while retaining water in the core assembly. Importantly, it does not filter out oil additives, preserving their catalytic effects. The purified oil is then returned to the tank for the next cycle, ensuring consistent cleanliness throughout the process. The KLEENOIL (Correno) ultrafiltration device has a high filtration accuracy and dirt capacity, capable of capturing up to 2500g of impurities and 780ml of water per filter. It can remove particles larger than 1 μm without clogging, offering a long service life and low maintenance costs. The device uses separate oil sampling tests to determine when to replace the filter or change the lubricating oil. Practical application has shown that using the KLEENOIL device can extend the life of lubricating or hydraulic oil by 5 to 10 times compared to traditional methods. In the gear pump manufacturing process, improvements in individual cleaning procedures have significantly reduced contamination levels. However, the brooming phenomenon during the test run is still inevitable. Combining an external circulation filtration system with the KLEENOIL ultrafiltration device has effectively solved the oil purification problem on the test stand, eliminating potential hazards and improving product quality. Currently, Hydraulics (Qingzhou) Co., Ltd. has designed its own external circulation filtration system and implemented the German KLEENOIL (Correno) ultrafiltration device. This has led to effective control of oil pollution, and the cleanliness of hydraulic gear pumps has been recognized by major OEMs both domestically and internationally.

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