Sunday, August 29, 2010

Why is the use of 10 valves

In the process of using the valve is not easy in a lot of attention, Ben Wang compiling answers to these questions, for the exchange of technical personnel



1, why is a small two-seater valve opening hours of work likely oscillation?



Pairs of single-core, when the medium is open-type flow, the valve stability; when the medium is a closed-type flow, the valve of the stability of the difference. There are two spool valve seat, the next spool in the flow of closed, open on the spool in the flow, so that a small opening in the work, the flow of closed-type valve spool is easy to cause vibration, which is two-seat valve can not be used for the work of a small opening reason.



2, why double-sealing valve as a shut-off valves can not be used?



Two-seat valve spool force balance the advantages of the structure, allowing large differential pressure, and its obvious drawback is that two sealing surface can not be good contacts at the same time, resulting in large leakage. If it is artificially Mandatory used to cut off occasion, apparently ineffective, even if it made a lot of improvements (such as the double-sealed sleeve valve), is also undesirable.



3, what straight poor performance, aiming to halt the stroke control valve, angle valve, prevent the travel of good performance?



Direct travel is vertical throttle valve spool, while the medium is the level of flow into the outflow valve cavity flow channel bound to turn down Shui Po, so that the valve flow path becomes quite complex (shape such as the inverted "S" type). In this way, there are many dead zone, the precipitation of the medium provides a space for the long run, causing blockage. The direction of travel throttle valve angle is the horizontal direction, the level of flows into the medium, the level of outflow, easy to clean media is not removed, flow path at the same time simple and very little room for medium precipitation, therefore, prevent the valve angle stroke of good performance.



4, why do straight stroke adjustment valve stem smaller?



It involves a simple mechanical principle: sliding friction, rolling friction small. Trip valve stem straight up and down movement, packing slightly pressed a little, it will stem bag tightly, resulting in a larger backlash. To this end, valve stem is designed to be very small, they often fill a small friction coefficient of PTFE packing, in order to reduce hysteresis, but the resulting problem is that stem thin sent, then the easy to bend, filling a shorter life expectancy. To solve this problem, the best way is to turn valve stem with the brigade, namely, the class trip valve angle, and its stem stroke than the straight stem crude 2 ~ 3 times, and the selection of long-lived graphite packing, valve stem stiffness Well, filling long life, but its friction torque is small, a small hysteresis.



5, why cut off the angle valve pressure class travel more?



Angle type valve to cut off travel greater pressure is due to media in the spool or the valve plate force generated by the rotational axis of the torque produced is very small, so it can withstand a greater pressure differential.



6, why the use of desalination water medium rubber lined butterfly valve, lined diaphragm valves and short service life?



Desalination of water medium containing low concentration of acid or alkali, they have a greater corrosive to rubber. Rubber showed expansion of corrosion, aging, low intensity, with the rubber lining of the butterfly valve, diaphragm use the results are poor, its essence is caused by corrosion of rubber impatience. After the rubber lining for Diaphragm Valves to improve corrosion resistance of a good Lining diaphragm valves, diaphragm valves of the diaphragm, but lined up and down then stand up to collapse were broken off, resulting in mechanical damage to valves shorter life expectancy. Now the best way to deal with specific water valve, it can use to 5 ~ 8 years.



7, why use a hard shut-off valve should be closed?



Shut-off valve required leakage as low as possible, soft-sealing valve leakage is the lowest cut off the effect is good, but not wear and poor reliability. From the leakage volume is small, sealed and reliable double standards, not as hard on the soft sealing off sealing off well. As a full-featured ultra-light control valve, sealing the heap are wear-resistant alloy protection, high reliability, leakage rate of 10-7, has been able to meet the shut-off valve requirements.



8, why sleeve valves instead of a single, two-seat valve does not wish fulfilled?



60 years came sleeve valve, 70 years large-scale use at home and abroad, and 80 years the introduction of the sleeve valve petrochemical plant accounted for a larger proportion of that time, many people think that the sleeve valve can replace a single, two-seat valve , to become the second-generation product. By now, is not the case, single-seat valves, seat valves, sleeve valves have been the same use. This is because the sleeve valve is throttling the form of improved stability and maintenance of better than single-seat valve, but it's weight, aiming to halt and leakage targets with single-seat valve in line, how can it replace the single-seat valve it? So, the only shared use.



9, Why is selection is more important than the calculation?



Calculation and selection of comparison, the selection should be much more important, much more complex. Because the calculation is a simple formula, which itself does not lie in the accuracy of the formula, but rather by the given parameters are correct. Selection related to the contents of the large, slightly careless, would lead to selection of properly, not only causes human, material and financial resources to waste, and use the result was unsatisfactory, and has brought a number of user issues, such as reliability, life, running quality.



10, why in the pneumatic valve in the piston executing agencies will be more and more?



For the pneumatic valve, the piston executing agencies may make full use of gas supply pressure, the executing agency of the size smaller than the membrane, a greater thrust piston in the O-ring and reliable than the film, so its use will Yuelai more. 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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