Weak current College】 【valve use frequently encountered 10 questions.

1. why two-seater valve small opening work easily on the oscillation?, when the single media type is stream open of the valve and good stability; when the media is closed, the stability of the valve. Two-seater valve has two valve, the valve is shut down, the stream is in flow open on the spool, so that the small open CV working, the stream is closed-type cartridge valves prone to vibration, this is the double seat valve can not be used for a small opening work.

2. Why is double-sealed valve can not be used as shut-off valve?
Two-seater valve valve core strengths is the force balance structure that allows the pressure difference, but it highlights the weaknesses are two seal cannot be good contact, resulting in the leakage. If you put it artificially, mandatory for cutting, obviously, and even as it made many improvements (e.g. double seal sleeve valve) or is not desirable.

3. what straight stroke control valve-proof performance, rotary valve anti-blocking properties?
Straight journey valve spool is vertical throttle, and media is a horizontal flow into the outflow valve cavity flow inevitably turn down turn, make the valve's flow path becomes quite complex (shapes such as inverted "S" type). Thus, there are a lot of dead time, as the medium of precipitation provides space, if this situation persists, causing clogging. Rotary valve raise our orientation is horizontal, the medium level into the standard, easy to take away the dirty media and at the same time flow path simple media precipitation space also rarely, rotary valve anti-blocking properties.

4. why straight journey valve stem smaller?
It involves a simple mechanical principle: sliding and rolling friction. Straight journey valve stem movement up and down, fill slight pressing point, it will turn the valve package is very tight and have a greater return difference. To this end, the design of very small stem, packing and commonly used small coefficient of friction, PTFE packing with a view to reducing the backlash, but it's problem is fine, it is easy to stem bent, packing life short. To solve this problem, the best way is to go with the Brigade, that is, the valve stem angle stroke class of the control valve, the valve stem than it straight trip stem rough 2 ~ 3 times, and the selection of the long life of graphite packing, stem rigidity, long-life packing, the frictional moment instead of small, small backlash.

5. why rotary valve shut-off pressure differential is large?
Rotary valve shut-off pressure differential is large, because the media at the valve or the valve plate on the axis of rotation of the force on the moment of very small, so that it can withstand a large differential pressure.

6. Why is demineralized water media using rubber-lined butterfly valve, fluorine diaphragm valve short service life?
Demineralized water media containing a low concentration of acid or base, they right rubber have greater corrosion. Rubber corrosion performance for expansive, aging, strength and low, with the glue of butterfly valves, diaphragm valve use effects are bad, its essence is corrosion-resistant rubber does not. After the glue and diaphragm valve for good corrosion resistance of Teflon diaphragm valve, but with fluorine diaphragm valve diaphragm by not being folded up and collapse, resulting in mechanical failure breaking, valve life short.
Now the best way is to use special-purpose ball valve for water treatment, it can use the 5-8 years.

7. Why is shut-off valve should try to use hard seal?
Shut-off valve requires disclosure of the lower, the better, and soft seal valve leakage is the lowest, cut off the result certainly good, but not wear-resistant, reliability is poor. From leakage and small, seal and reliable double standard, soft sealed shut-off as hard sealed shut-off. As a full-featured ultra-light control valve, seal and heap are wear-resistant alloy protection, high reliability, leakage rate of 10-7, has been able to meet the requirements of the shut-off valve.

8. why sleeve valve in place of single and two-seater valve did not do?
The advent of the 60 's, 70 's sleeve valve in extensive use at home and abroad, the 80 's introduction of petrochemical plant sleeve valve of larger, at that time, many people believe that the sleeve valve can replace single and two-seater valve, a second generation product. Until now, this is not the case, single seat valve, two-seater valve, sleeve valve are equal. This is because the sleeve valve just improved throttle forms, stability and maintain better than single seat valve, but its weight, proof and leak indicators and single and two-seater valve, it can replace single and two-seater valve? so that it can only common use.

9. Why is more important than the calculation and selection?
Calculation and selection of comparison, selection is much more important, much more complex. Because it is just a simple formula, it is not in itself, but the formula of accuracy is the given process parameters is accurate. Selection involves more of content, a little careless, leads to selection of inappropriate, not only causes human, material and financial resources of the waste and the use effect is also not ideal, bring some use issues, such as reliability, quality of life, running, etc.

10. Why is the pneumatic valve piston actuators use more?
For pneumatic valves, piston actuator can take full advantage of the air pressure, so that the actuator dimensions smaller than film, thrust, the piston o-rings are also reliable than film, therefore its use is increasing.