Introduction to the selection of the hottest shut-

Introduction to cut-off valve selection

selection of structural type

in terms of cut-off effect, angle travel valve has simpler structure, more reliable sealing effect and more advantages than straight travel valve (such as single seat valve, sleeve valve, gate valve, etc.). Three eccentric hard seal butterfly valves and ball valves are more representative

selection of sealing surface

1) face to face sealing:

the sealing surface of common plunger valve elements is a small conical surface of 60 °, and the width of this small conical surface is usually between 0.5mm and 2mm. To seal well, it is necessary to ensure good contact between the two conical surfaces. 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 be achieved after precision grinding, and can reach a higher sealing grade

2) spherical seal

the spherical rotation of the spherical surface is tangent to the fixed valve small cone, and they are in line contact, which is better than the above face-to-face sealing effect. Ball valve and spherical sealing butterfly valve are made with this idea, and their leakage rate can reach ~, and high-performance triple eccentric butterfly valve can reach, or even zero leakage

selection of sealing materials

1) soft seal

except for the corrosion-resistant lined valve, the general soft seal valve refers to the valve whose valve core or valve seat adopts the sealing form of metal material (the system will check the authority of the operator, mainly polytetrafluoroethylene and rubber, do not know the steel structure, do not want to adopt the steel structure, 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, increase 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 then surfacing wear-resistant alloy is 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

reliability of shut-off valve

1) soft sealing, good cutting effect, but 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 "O" type ball 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, wear-resistant alloy must be overlaid on the cut-off regulating valve with leakage requirements above to improve the wear resistance, erosion resistance and scratch resistance of the seal and improve the service life of the valve

3) it has experimental power to cut off high-temperature medium. The digital display control valve is assembled at room temperature and works at high temperature. The temperature changes by several Baidu. Thermal expansion will change the seal specific pressure established during assembly. If it is too tight, the sealing surface will jam, 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. It has both flexibility to overcome thermal expansion and rigidity, and surfacing wear-resistant alloy to improve the reliability of wear-resistant surface

4) for the erosion medium containing particles, the valve core should be considered to avoid the direct erosion of high-speed medium

5) for hard seals, there must be enough hardness difference. Materials with the same hardness "do not yield to each other", which is easy to scratch and cause leakage

selection of main valve types of shut-off valve

as mentioned above, the main valve types of shut-off valve are as follows. The selection of shut-off valve should comprehensively consider various parameters such as leakage rate, medium type, medium temperature, flow coefficient and cost performance. In the following optimization sequence, first consider the hard seal, such as mairuibao, which we are familiar with, and then consider the soft seal

1) three eccentric metal hard seal butterfly valve

2) double eccentric spherical seal butterfly valve

3) ball valve

4) eccentric rotary valve

5) single seat valve

6) sleeve valve

7) soft seal valve