The principle and main features of dry gas seal for pump

The principle and main characteristics of the dry gas seal for pumps 1. Working principle The dry gas seal for pumps is a new type of high-performance and long-life seal. The structure of the seal factory is obviously different from the usual mechanical seals: dynamic , The static ring seal has a wide end surface; a special shape of fluid dynamic pressure groove is machined on the end surface of the moving ring or the static ring, such as a spiral groove, and the groove depth is usually between 3-10pm. When the mechanical seal of the moving ring high-speed pump rotates, the spiral groove on the end surface of the moving ring or the static ring pumps the high-pressure gas at the outer diameter of the mechanical seal factory down into the seal end surface, and the gas flows from the outer radial base to the seal. The dam restricts the flow of gas to the base, so the gas is compressed and the pressure rises, forming a high-pressure zone at the root of the groove. The air film pressure on the end face constitutes an opening force. When the seal works stably, the opening force is balanced with the closing force formed by the gas pressure on the opposite side of the compensation ring and the tension spring force. The seal maintains non-touch and wear-free work. The thickness is usually maintained at 2-3pm. If there are some disturbance elements that reduce the sealing gap, resulting in a reduction in the opening force, while the closing force remains unchanged, the sealing gap will be reduced, and the seal will quickly recover and balance again. The ability of dry gas sealing to resist changes in the air film gap is called air film stiffness. Although the air gap of the dry gas seal of the pump is small, the rigidity of the air film is very large, which is much greater than that of the liquid film smooth mechanical seal. 2. The main advantages Compared with traditional touch mechanical seals, the use of dry gas seals in centrifugal pumps has the following advantages: (1) The conflicting power consumption is low because the two sealed end faces of the dry gas seal are stabilized by a thin layer. The gas film is blocked and the sealed cavity is a low-viscosity gas medium. Therefore, the conflicting power consumption of the end face of the dry gas seal and the mixing conflict loss of the moving ring assembly are much less than the conflicting power consumption of the liquid smooth sealing device, and usually both cost The power ratio is about 1:10-20. (2) Wear-free work, long service life, dry gas seal, because the two oppositely rotating ends face the wrong touch, under normal operating conditions, it can usually reach over 3 years. (3) No sealing liquid system, zero leakage or zero overflow sealing liquid system that can complete the pumping medium is often messy and expensive, and there is an inevitable risk of failure. The external leakage of the pumped medium and the cooling and sealing of the sealing liquid depend on the perfection of the sealing liquid system. The dry gas seal avoids all these messy elements. It uses a dry and clean nitrogen source as the sealing gas. It is very simple to achieve zero leakage or zero overflow of the pumping medium, without any pollution to the pumping medium, and the system is relatively simple and reliable. high. 3. Primary technical difficulties Compared with dry gas seals for high-speed turbocompressors, there are three difficulties with dry gas seals for centrifugal pumps: (1) Structural dimensions are restricted. The radial space of the stuffing box of centrifugal pumps is relatively small, especially the transformation of some old pump shaft seals, the problem is even more outstanding. In this way, usually the sealing surface of the dry gas seal for pumps is relatively narrow, because the sealing surface must include the groove area for downward pumping effect and the dam area for sealing effect. Therefore, the end surface structure of the pump with dry gas seal The planning of parameters (including the few parameters of the runner) is not the same as that of the dry gas seal for turbo compressors, and it is more difficult. (2) The speed is low, and the dynamic pressure effect is small. Because the spindle speed of the centrifugal pump is not high, in order to improve the air film stiffness of the seal under the working film thickness as much as possible to enhance the reliability of the seal work, special consideration is necessary in the selection of the end groove and the optimization of the structural parameters. (3) High performance quotation ratio. Because the value of the centrifugal pump machine itself is much smaller than that of the turbo compressor, the quotation of the dry gas seal for the pump is much lower than that of the dry gas seal for the turbo compressor, which requires its performance quotation. Very high than necessary. Therefore, when planning the dry gas seal and its control system for pumps, under the premise of ensuring the seal and system performance, it is necessary to fully consider its economy to facilitate the popularization and application of dry gas seals for pumps, which increases the sealing and Difficulty of system planning and production. Keywords: seal factory, mechanical seal factory, pump mechanical seal