Purchasing methods and types of the hottest shut-o

The selection method and type of shut-off valve

the shut-off requirements will be put forward for the regulating valve in the application occasions with high requirements. Therefore, the shut-off function is an important use function and internal quality index of the regulating valve (see relevant data for the division and standard of the shut-off grade). In field use, there are often failures such as poor shut-off of the regulating valve and large leakage. In addition to the increase in leakage caused by blockage and jacking due to too small allowable differential pressure, most of them are caused by structural defects and improper selection of control valves

I. selection of structural type

one of the main disadvantages of double seal regulating valves (such as double seat valves, double seal sleeve valves, etc.) is large leakage. However, before the 1980s of the 120 ° diamond conic period in the world, sleeve valves were more popular at that time. However, many manufacturers made great efforts to improve the structure of sleeve valves to reduce leakage and make them evolve into very complex structures. As a result, this has brought many deficiencies: many parts, poor reliability, difficult spare parts, difficult maintenance, poor cutting effect and so on. In fact, this is a mistake in the design idea. Instead of making such complex changes in the "heart" of the valve body, it is better to realize it through external adjustment. Therefore, single seal regulating valve should be selected. In this way, the problems of sealing, reliability, maintenance and spare parts have been solved one by one. At this time, the key to solve the contradiction is to increase the unbalanced force of the medium on the valve. It only needs to be equipped with a strong piston actuator and a thickened valve stem. This solution through external is obviously much easier than internal complex improvement. It is not so much a problem of method as a problem of thinking. In the 1990s, people began to look for cut-off valves with simpler structure and more reliable sealing. At this time, it was found that the angle travel valve had more advantages than the straight travel valve (single seat valve, sleeve valve, gate valve), so three eccentric cut-off butterfly valve, full-function cut-off valve and hard seal cut-off ball valve were produced

II. Selection of sealing surface

(1) face to face sealing:

the sealing surface of common plunger valve elements is a small cone of 60 ℃, and the valve seat is also a small cone of 60 ℃. The width of this small cone is usually between 0.5mm and 2mm. To seal well, we must ensure that the two cone surfaces are in good contact. But in fact, it is always affected by processing errors (such as centrality, out of roundness, inclination, etc.), and its sealing effect is not very ideal. The leakage rate of this kind of valve is usually, which can only reach a better sealing grade after precise grinding

(2) spherical sealing:

use the spherical rotation of the valve core to be tangent to the small conical surface of the fixed valve seat, and they are in line contact, which is better than the above face-to-face sealing effect. The full-function ultra light valve and spherical sealing butterfly valve launched by Hualin company are made with this idea. Its leakage rate can reach ~, and the high-performance triple eccentric butterfly valve can reach as high as zero leakage

III. selection of sealing materials

(1) soft sealing

in addition to the corrosion-resistant lined valve, the general soft sealing valve refers to the valve core or valve. Welcome to visit our large manufacturer of Jinan new era Gold Testing Instrument Co., Ltd. one of the two is a valve in the form of sealing with non-metallic materials (mainly polytetrafluoroethylene, rubber, etc.). The sealing effect of the soft seal valve is the best, but there may be more or less unclean sundries (such as welding slag, iron filings, etc.) left in the pipeline installation and system cleaning. When they flow through the regulating valve, they are easy to scratch the soft seal valve seat or valve core, increasing the leakage and poor sealing reliability. Therefore, the selection of soft sealing structure must consider the cleaning of the medium and the strict flushing of the pipeline before operation

(2) hard seal

hard seal and surfacing wear-resistant alloy are the best choice for shut-off valve. This method not only considers the sealing performance, but also considers the service life and reliability. Although the ex factory index is only ~, which cannot achieve the effect of zero leakage of soft seal, it is enough to meet the requirements of tight cutting, and it is durable, which is more cost-effective from an economic point of view

IV. consideration of sealing reliability

(1) soft sealing has good cutting effect, but it is not suitable for granular media. Once scratched, the leakage will increase sharply. Therefore, hard sealing should be selected as far as possible when conditions permit. The hard seal of full-function ultra light valve can reach ~, and the three eccentric butterfly valve can reach zero leakage

(2) consideration of seal wear resistance: in addition to selecting hard seal, the cut-off regulating valve with leakage requirements above should (or must) be overlaid with wear-resistant alloy to improve the wear resistance, erosion resistance and scratch resistance of the seal and improve the service life of the valve

(3) the shut-off regulating valve for high-temperature medium is assembled at room temperature and works at high temperature, with a temperature change of several Baidu. Thermal expansion will change the seal specific pressure established during assembly. If it is too tight, the sealing surface will get stuck, and it will be seriously scratched and strained during movement; If it is too loose and the sealing pressure is not enough, the leakage will increase sharply in both cases. The best solution is to use elastic valve seat to absorb the difference caused by this change. There are usually three elastic schemes: ① spring type; ② Sheet type flexible metal ring; ③ Elastic valve seat with hardness and softness. The latter is the best, that is, it has flexibility to overcome thermal expansion, and it has rigidity to stack wear-resistant alloys to improve the reliability of wear-resistant surfaces

(4) for the erosion medium containing particles, the motor is installed outside, and the valve core should be considered to avoid the direct erosion of high-speed medium. Straight stroke valve and butterfly valve do not have this function, while the eccentric rotation of full-function ultra light valve has this feature. In this case, the latter two valves should be selected

(5) for hard seals, there must be enough hardness difference, and materials with the same hardness are "not in competition with each other", which is easy to scratch

(6) the thrust and stiffness of the equipped actuator should be increased to make it move freely

v. main valve types of shut-off valves

according to the above analysis, the main valve types of shut-off valves are as follows. The selection of shut-off valves should comprehensively consider the leakage rate, medium type, medium temperature, flow coefficient and other parameters and cost performance. In the following preferred order, the hard seal shall be considered first, and then the soft seal

(1) full function ultra light regulating valve

(2) trade cooperation with China will be put on the agenda) three eccentric metal hard seal butterfly valve

(3) double eccentric spherical seal butterfly valve

(4) ball valve

(5) eccentric rotary valve

(6) single seat valve

(7) single seat sleeve valve

(8) soft seal valve

VI. selection of high temperature, high pressure, large differential pressure and large diameter shut-off valve

high temperature, high pressure, large differential pressure Large diameter cut-off is a common problem, mainly due to the lack of valves with large allowable differential pressure, good cut-off and high temperature resistant expansion cards, such as high-pressure steam regulation and cut-off. Due to the large differential pressure (1 ~ 3Mpa or more) and large diameter (DN200 ~ 300), balanced double seal structure (such as double seat valve or double seal sleeve valve) has to be adopted. After special treatment, the leakage rate can reach, and it is difficult to improve again, The comprehensive performance of the full-function ultra light regulating valve is good, which can better solve this problem, and the leakage rate can reach more than