There are ten common problems in the use of knife gate valves
One, why double seat valve small opening work is easy to oscillate
For single-core knife gate valve, when the medium is open-type, the valve stability is good; when the medium is closed, the valve stability is poor. Double seat valve has two spool, the lower spool in the flow closed, the spool in the flow open, so that in the small opening work, the flow closure of the valve core is easy to cause the valve vibration, which is double seat valve Can not be used for small opening work of the reasons.
Second, why double sealed valve can not be used as a shut-off valve
The advantage of the double seat valve spool is the force balance structure, which allows the pressure difference to be large, and its outstanding drawback is that the two sealing surfaces can not be in good contact at the same time, resulting in large leakage. It is not advisable to make a lot of improvements (such as double-seal sleeves) if it is artificially and forcefully used for cutting applications.
Third, what straight trip valve anti-blocking performance is poor, angular travel valve anti-blocking performance
Straight stroke valve spool is a vertical throttling, and the media is horizontal into and out of the flow, knife gate valve the valve cavity flow channel must turn down the turn, so that the valve flow becomes quite complex (shape such as inverted "S" type). In this way, there are many dead zones that provide space for the precipitation of the medium, which in the past causes clogging. Angle travel valve throttling direction is the horizontal direction, the media level into the horizontal outflow, easy to clean the media away, while the flow of simple, medium precipitation space is also very small, so the angle of the valve anti-blocking performance.
Four, why straight stroke valve stem finer
It involves a simple mechanical principle: sliding friction is large, rolling friction is small. Straight stroke valve stem up and down movement, packing slightly pressed a little, it will be very tight valve stem, knife gate valve resulting in a larger hysteresis. To this end, the stem is designed to be very small, the filler is often a small friction coefficient of PTFE filler, in order to reduce the hysteresis, but the problem is sent stem fine, easy to bend, filler life is short. To solve this problem, the best way is to use the travel valve stem, that is, the angle of the class of the control valve, and its stem stem straight stroke than 2 to 3 times, and the choice of long life graphite packing, stem stiffness Well, the filler life is long, the friction torque is small, the hysteresis is small.
Five, why the angle of the valve class cut off the larger pressure?
The angular pressure of the angle travel valve is large because the resultant force on the spool or valve plate is very small for the rotating shaft, knife gate valve so it can withstand a large pressure difference.
Six, why desalination water medium using rubber lined butterfly valve, lined diaphragm valve short service life?
Desalted water medium contains low concentrations of acid or alkali, they are more corrosive to rubber. Rubber corrosion is manifested as expansion, aging, low strength, with rubber lined butterfly valve, diaphragm effect is poor use of its essence is due to rubber corrosion. Back rubber diaphragm valve improved corrosion resistance for the good performance of the fluorine diaphragm valve, but the lining of the diaphragm diaphragm can not withstand the folding up and down and was broken, resulting in mechanical damage, the valve life shorter. Now the best way is to use water treatment dedicated ball valve, it can be used to 5 to 8 years.
Seven, why cut off the valve should try to use hard seal
Cut off the valve required to leak the lower the better, soft seal valve leakage is the lowest, cut off the effect of course, but not wear, poor reliability. From the leakage of small, sealed and reliable double standard, knife gate valve the soft seal cut off as hard seal cut off. Such as full-function ultra-light control valve, sealed and heap wear-resistant alloy protection, high reliability, leakage rate of 10 to 7, has been able to meet the requirements of shut-off valve.
Eight, why the sleeve valve instead of single, double seat valve did not do so wish
In the 1960s, the sleeve valve was introduced at home and abroad. Seat valve, become the second generation of products. To this day, is not the case, single seat valve, double seat valve, sleeve valve are the same use. knife gate valve This is because the sleeve valve is only improved in the form of throttle, stability and maintenance is better than single seat valve, but its weight, anti-blocking and leakage indicators with single and double seat valve consistent, how can it replace single, double seat valve What? So, can only be used together.
Nine, why the selection is more important than the calculation
Calculation and selection of comparison, the selection is much more important and more complex. Because the calculation is only a simple formula to calculate, it itself is not the accuracy of the formula, but rather whether the given process parameters are accurate. Selection of the content involved more, a little careless, it will lead to improper selection, not only caused by human, material and financial waste, and the use of the effect is not ideal, bringing a number of problems, such as reliability, Quality and so on.
10, why in the pneumatic valve piston actuator will be used more and more
For pneumatic valves, the piston actuator can take full advantage of the air supply pressure, making the actuator size smaller than the film, the thrust is greater, knife gate valve the piston O-ring is also more reliable than the film, so its use will be more and more many.