First, why the double seal valve can not be used as a shut-off valve
Seat valve spool advantage of the structure of the force balance, allowing the pressure large, and it highlights the shortcomings of the two sealing surface can not be a good contact, resulting in a large leak. If it is artificially mandatory for cutting off occasion, it is clear that the effect is not good, even if it made a number of improvements (such as double sealing sleeve valve) is not desirable.
Second, why the small opening of the double seat valve easy to oscillation
For single-core, when the media is open - type flow, the valve stability; when the medium is the flow of closed type, the stability of the valve. Seat valve has two spool, spool in the flow of closed on the spool in the open flow, so that the small opening, the flow closed spool is easy to cause the vibration of the valve, which is double seat valve not the reason for the small opening.
Third, what straight trip poor attempts to prevent the performance of the valve, angle valve attempts to prevent performance
Straight travel valve spool is the vertical throttle, and the medium is the horizontal flow into and out of the the valve cavity flow channel must turn back street, so that the valve flow path becomes quite complex (shape, such as the inverted S-shaped). In this way, there are many dead-space, over time, as the medium of precipitation, causing blockage. Throttle valve angle of the direction is the horizontal direction, flowing into the medium level, the level of outflow, easy to take away the medium is not clean, the flow path is simple, medium precipitation space rarely, so attempts to prevent the performance of the rotary valve.
Fourth, why rotary type valve to cut off large pressure difference?
Rotary type valve to cut off a large pressure difference is very small, the torque generated on the rotating shaft because of the force generated by the medium of the spool or the valve plate, therefore, it can withstand greater pressure.
Why the straight stroke adjustment valve stem smaller
It involves a simple mechanical principle: sliding friction, rolling friction. Linear actuator valve stem moves up and down, packing slightly compressed that it will stem a very tight package, resulting in a greater backlash. Stem design is very small, a small coefficient of friction PTFE packing another commonly used filler, in order to reduce the hysteresis, but the problem is thus sent the stem, is easy to bend, packing life is short. To solve this problem, the best way is with a tour to turn valve stem or rotary type control valve, the valve stem stroke than a straight stem crude 2 to 3 times, and the choice of long life graphite packing, stem stiffness Good, filling long life, the friction torque but small, small hysteresis.
Sixth, why desalinated water medium using rubber lined butterfly valve, lined diaphragm short life?
Desalting the aqueous medium containing a low concentration of acid or alkali, larger corrosive rubber. Rubber corrosion showed expansion, aging, low intensity, rubber lined butterfly valves, diaphragm valves use of effects are worse in essence, rubber impatient corrosion. After rubber lined diaphragm to improve corrosion resistance good lined diaphragm, lined diaphragm diaphragm and stand up to the upper and lower folding were broken off, resulting in mechanical damage, the shorter the life of the valve. Now the best way is for water treatment valve, it can be used to 5 to 8 years.
7, why shut-off valve should try to use the hard seal
Shut-off valve leakage as low as possible, soft seal valve leakage is the lowest cut off the effect is good, but do not wear, poor reliability. From leakage, sealing and reliable double standards, the soft seal cut is not as good as hard seal cutting. Such as full-featured ultra-light control valve, sealing the reactor with the protection of the wear-resistant alloy, high reliability, leakage rate of 10 to 7, have been able to meet the requirements of the shut-off valve. |
