Sealing Technology and Analysis of Hydraulic Valve

The service life of various hydraulic valves in the hydraulic support is very low. The foreign solution is to improve the filtration accuracy of the system and improve the quality of the emulsion, but the effect is not large. This paper analyzes the development process of the sealing pair of the bracket valve, and discusses the relationship between the material of the sealing pair and the sealing performance. It is pointed out that the sealing technology is the key to improve the service life of the hydraulic valve in the hydraulic support. Hydraulic support is the supporting equipment in coal mining machinery. After overhaul, it can generally be used underground for five years. However, the service life of various hydraulic valves in the hydraulic support is very low. The long is 3 months, and the short is only a few weeks. The foreign solution is to increase the filtration precision of the system and improve the quality of the emulsion, but the effect is not large. Taking a hydraulic valve in the UK as an example, although the machining accuracy and the filtration accuracy of the entire hydraulic system are relatively high, it has been eliminated in my country due to its low service life.

1. Main factors affecting the sealing performance of hydraulic valves The main factor for seal damage is impurities in the working fluid. These impurities grind between the seals, causing the valve to leak. Therefore, foreign countries have proposed hydraulic components of corresponding grades, and filters of corresponding precision should be used. They believe that the life of 5M oil pump seals can be increased by 10 times compared with the use of 10µM filters if a filter with a filtration accuracy of 3/M is used. However, the working environment of the valve for hydraulic support is very harsh. In the coal mining face, the total length of the oil pipe is more than 1,000 meters, and there are more than 4,000 joints and sockets, and the liquid tank has no special dustproof facilities. There are a lot of floating impurities in the emulsion, and there are more coal powder, rock particles and iron filings at the bottom of the cylinder and the valve cavity. Inlet valve core and valve seat, due to frequent opening and closing, high liquid flow rate, the seal will soon fail. Practice has proved that it is very difficult to reduce the contamination and impurities of the hydraulic system of the support. Some people once imagined that a high-pressure filter should be used in the emulsion pump station, and a small filter should be added at the inlet of each support. But it was quickly blocked during work, resulting in a cutoff. On the other hand, with the development of hydraulic support technology. Higher requirements are placed on the performance of the valve and the service life of the valve. At present, the life of the valve is measured by the total flow of the emulsion through the tested valve and the number of times the valve is opened and closed with a 120-mesh filter and a magnetic filter device installed. But in fact, the indoor type test is quite different from the actual work results in the well. At present, the formal experiments in many countries have increased the anti-pollution requirements. Some are mixing appropriate pulverized coal in the emulsion, and some are adding mechanical impurities. To this end, it is necessary to use a new type of sealing pair with strong anti-pollution ability and suitable for underground working conditions.

2. History and current situation of hydraulic valve sealing materials

The leakage of the contact surface between the valve core and the valve seat is the result of the intrusion of the working liquid molecules. The main reasons that affect the sealing effect are the contact specific pressure, unevenness and pressure difference between the valve core and the valve seat. When the joint surface of the valve core and the valve seat is pressed with P force, the working liquid molecules are squeezed in with F force, and the sealing material will be elastically deformed. If the total resistance of the seal pair is greater than the molecular repulsion, the seal is effective, otherwise leakage will occur. In the early hydraulic support, there were no other sealing measures between the moving pairs, and the metal was directly contacted and sealed, that is, the contact plane of the sealing pair was required to match, and it had high machining accuracy. Otherwise, the bonding force of the sealing pair must be increased to make the contact surface plastic. Deformation, blocking leakage channels.