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 trial run of these pumps in the factory, a phenomenon known as "brooming" occurs, which generates pollutants. These contaminants can directly affect the hydraulic test system. With current conventional oil pollution control technologies being limited, residual oil inside the pump can further contaminate it, reducing the reliability of the hydraulic system. As a result, research into oil purification technology for gear pump test stands has become a major focus in 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 conducted an analysis at Shandong Runuang Hydraulic Technology Co., Ltd. (now Haldex (Qingzhou) Co., Ltd.), a large and representative company in the gear pump industry. The results showed that the oil cleanliness level reached NAS 1638-13, indicating serious contamination. Over 80% of the particles were between 10–30 μm, primarily due to the brooming effect during testing. Since most pump bodies are made of aluminum alloys, these particles remained suspended in the oil. As testing frequency increased and time passed, oil cleanliness deteriorated rapidly, leading to a decline in oil performance and test results. Residual oil inside the pump also posed long-term risks for future use. Previously, the company had to frequently replace test oil and clean the pumps after each test, resulting in significant waste of resources. This oil pollution issue became a critical problem that affected the company's development and drew widespread attention within the industry.
To address this, we analyzed and compared different solutions and concluded that, due to the design of the gear pump, the brooming phenomenon is unavoidable. Therefore, the only way to fundamentally solve the oil pollution problem is through advanced cleaning equipment at the test system level. Such equipment must have high dirt capacity and filtration accuracy. We recommended introducing the German KLEENOIL ultrafiltration device next to the oil tank. This device uses polypropylene fiber media, offering excellent particle retention and dehydration capabilities. It effectively filters particles larger than 1 μm while keeping water trapped in the core assembly. Oil additives remain unaffected, ensuring they continue to function properly. The purified oil is then returned to the tank for the next cycle, meeting all test requirements after several cycles.
The KLEENOIL (Correno) ultrafiltration device has a high filtration accuracy and dirt capacity, capable of holding up to 2500g of impurities and 780ml of water. It can remove more than 1μm particles 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 (Correno) device can extend the life of lubricating oil or hydraulic oil by 5 to 10 times.
Although improvements in individual cleaning processes during gear pump production have helped reduce pollution, the brooming phenomenon during testing remains inevitable. By combining an external circulation filtration system with the KLEENOIL (Correno) ultrafiltration device, the oil purification issue on the test stand has been effectively resolved, eliminating hidden dangers and improving product quality.
Currently, Haldex (Qingzhou) Co., Ltd. has designed its own external circulation filtration system and implemented the German KLEENOIL (Correno) ultrafiltration device. This has effectively controlled oil pollution, and the cleanliness of the hydraulic gear pump products has been recognized by major OEMs both domestically and internationally.
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