In demanding applications will be submitted to the regulating valve to cut off expectations, and thus cut off the valve function is an important function and the use of internal quality indicators (right off the division level and standards in the relevant information). Use in the field often appear cut off valve is not good, big and leakage fault. In addition to a result of a trap, allowing the small pressure difference was caused by such factors as the top open to increase the leakage, the vast majority are due to structural valve defects and caused by improper selection.
First, the choice of structure type
Double sealed class regulator valve (such as seat valves, double seal sleeve valve, etc.) is one of the major shortcomings of large leaks. But the last century, 80 years ago, because at that time than the prevalence of the sleeve valve, however, many manufacturers are in the sleeve valve up and down a lot effort to improve the structure to reduce the leakage rate, it evolved into a very complex structure. So, this brings a lot to be desired: many spare parts, reliability is poor, spare parts difficult, maintenance is difficult to cut off the result is not satisfactory and so on. In fact, this is the design ideas are all misunderstanding, rather than in the body of the "heart" in making such a complex changes, it would be better achieved through external adjustment. Therefore, we should choose a single seal type valve. In this way, sealing problems, reliability problems, maintenance and spare parts were 11 problems solved. At this time, resolving contradictions into the focus of media on the unbalanced forces in the increased valve trouble, that it only with a strong executive body piston, valve stem can be bold. Such external to the solution is clearly more than the complexity of internal improvements to be much easier approach to the problem is not so much, might as well say that this is a thinking problem. Into the nineties, people began to look for structure is more simple, more reliable sealing of the shut-off valve. At this time, found that stroke valve angle valve stroke than a straight (single seat valve, sleeve valve, gate valve) is more superior, the question arose three eccentric butterfly valve to cut off, full-featured shut-off valve, hard seal cut off the ball.
Second, the choice of sealing surface
(1) face to face sealing:
A common plunger valve core, the sealing surface of a small cone at 60 ℃, 60 ℃ seat is a small cone, the width of this mini-cone usually 0.5mm ~ 2mm between the guarantee must be sealed well to be two cone good contacts. But in fact, it has always been the impact of processing errors (as in the heart of a no roundness, tilt, etc.), which sealed the result is not very satisfactory. Such valves typically leak rate of 10-4, after precision grinding of up to 10-6, only to achieve a better seal level.
(2) sphere Seal:
The use of spool rotation and a fixed spherical cone tangent to the small seat between them as the line of contact, and this effect than the above face to face with a good seal. Waring has introduced a full-featured ultra-light valve, the spherical sealing butterfly valve and so on is to adopt this line of thought to create, and its leakage rate of up to 10-6 ~ 10-8, high-performance three-eccentric butterfly valve can be as high as 10-8 , as well as zero leakage.
Third, the choice of sealing materials
(1) Soft Seal
In addition to corrosion-resistant lining valves, in general, the soft seal spool valve or a valve seat one of these two means using non-metallic materials (mainly PTFE, as well as rubber, etc.) form of valve sealing. Soft sealing valve seal is best, but in piping installation, the system of cleaning that could have left more or less does not clean debris (such as welding slag, scrap iron, etc.), which flows through the valve, it is easy to Soft sealing valve seat or valve core scratch, so that leakage increased, the reliability of sealing difference. Therefore, the choice of soft sealing structure must take into account the medium cleaning and put into operation before the stringent wash pipe.
(2) Hard Seal
Hard seal re-surfacing wear-resistant alloy such as shut-off valve is the best choice. In this way, while taking into account also taken into account seal life and reliability, although the factory index is only 10-6 ~ 10-8, reaching less than a soft seal zero leakage effect, but enough to meet the rigorous requirements of cut off, and it durable, from the economic point of view to consider more cost-effective.
4, sealing reliability considerations
(1) soft sealing, cutting effect is good, but not suitable for containing granular media, once scratch, leakage would increase drastically. Thus, when conditions permit have tried to use a hard seal. Full-function ultra-light valve Hard Seal up 10-7 ~ 10-8, the three eccentric butterfly valves up to zero leakage.
(2) The wear resistance of the sealed consideration: In addition to a hard seal the election, the right to cut off leakage requirement of more than 10-6 type control valve, it should be (or must) surfacing wear-resistant alloy to improve the seal wear resistance, resistance to erosion, scratch-resistant ability, improve valve life.
(3) medium to high temperature cut-off control valve assembly at room temperature, and in working under high temperature, the temperature changes of a few hundred degrees. Thermal expansion will change the seal assembly, to establish specific pressure. Too tight, sealing surface will be stuck, sport will be severely bruised, strained; too loose, sealing pressure is not enough in either case, leakage would be increased dramatically. The best way to solve is to use elasticity of the valve seat to absorb the difference caused by this change. Usually have three kinds of flexibility in the program: ① spring; ② Flexible sheet metal ring; ③ hardness and softness of the flexible seat. The latter is best, that is flexible to overcome the thermal expansion, stiffness, and there are heaps to improve the wear-resistant surface wear-resistant alloy reliability.
(4) The erosion medium containing particles should be considered open spool avoidance of direct high-speed media erosion. Straight trip valves, butterfly valves do not have this feature, while the full-featured ultra-light eccentric rotary valve has this characteristic. Case of this, two kinds of valves should be after the election.
(5) For hard-seal, there must be sufficient hardness difference, the same hardness material "each side", were easily scratched.
(6) of the implementing agencies should be increased with thrust and stiffness make it moves freely.
5, the main valve shut-off valve-type
According to the above analysis, the main valve shut-off valve types are as follows, choose the shut-off valve should be integrated to consider leakage rates, media types, media temperature, flow coefficient and other parameters and cost-effective. In the following preferred order, first consider the hard seal, consider a soft seal.
(1) full-featured ultra-light control valve
(2) 3 eccentricity metal hard sealing butterfly valve
(3) The double eccentric butterfly valve ball seal
(4) Ball
(5), Eccentric Rotary Valve
(6) Single-seat valve
(7) single-seat sleeve valve
(8) Soft Seal Valves
6, high temperature, high pressure, big pressure, large diameter shut-off valve selection
High temperature, high pressure, large differential pressure, large diameter cut is a relatively common problem, mainly due to the lack of pressure also has to allow large, cut off the good, high-temperature expansion cards of the valve, such as the high-pressure steam conditioning and cut off, due to pressure large (1 ~ 3MPa or greater), diameter large (DN200 ~ 300), forced to adopt a balanced-type double-seal structure (such as two-seater double-sealed sleeve valve or valves), after special treatment, leak rate of up to 10-4 further increases the difficulty, while the full-function ultra-light valve combination of properties, and can be a better solution to this problem, leakage rate can reach more than 10-6 ~ 10-7. ball valve Trunnion Mounted Ball Valve Floating Ball Valve Top Entry Ball Valve Three way ball valve V Type Ball Valve
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