Valves used in the Frequently Asked Questions

Valves used in the Frequently Asked Questions
First, why the double-seal valve can not be used as a cut off valve
Seat valve spool force balance the advantages of structure, allowing a large pressure difference, but it highlights the shortcomings of the two can not both be a good contact with the sealing surface, causing a large leak. If it artificially, mandatory for cutting off occasion, obviously not good, even if it made a lot of improvements (such as double-sealed sleeve valve), is also undesirable.
Second, why is a small two-seat valve opening is easy oscillation work
On single-core, when the medium is open stream type, the valve stability; when the medium is the flow of closed type, the valve of the poor stability. There are two spool valve seat, the next in a flow valve closed, the valve is open flow, so that small opening in the work, the flow of closed-type valve spool is easy to cause vibration, this is the two-seat valve can not work for small opening reason.
Third, any attempts to prevent the performance of straight travel valve bad, good performance rotary valve attempts to prevent
Straight trip throttle valve spool is vertical, while the medium is the level of flow into the outflow valve cavity flow must turn back street, so that the valve flow path become very complex (such as inverted S-shape). Thus, there are many dead, as the medium of precipitation provides a space for the long run, causing blockage. Throttle valve angle of the direction of travel is the horizontal direction, the level of flow into the medium, the level of outflow, easy to medium is not clean away, a simple flow path at the same time, media space and few precipitation, so rotary valve attempts to prevent the performance is good.
Fourth, why the rotary valve to cut off pressure higher class?
Rotary type valve to cut off large pressure difference is due to media at the spool or valve on a board together to produce the torque on the rotation axis is very small, so it can withstand greater pressure.
Five, why straight trip valve stem smaller
It involves a simple mechanical principle: a large sliding friction, rolling friction small. Linear actuator valve stem up and down movement, packing slightly compressed that it will stem a very tight package, have a greater backlash. To this end, stem design very small, another commonly used filler of PTFE packing friction coefficient in order to reduce backlash, but this problem is to send small stem, is easily bent, packing too short life. Solve this problem, the best way is to turn valve stem with a tour, or rotary type control valve, and its thick stem stroke than a straight stem 2 to 3 times, and use long life of the graphite packing, valve stem stiffness Good, filling long life
The friction torque but small, small backlash.
6, why desalination water medium using rubber lined butterfly valve, fluorine diaphragm short life?
Desalination of water medium containing low concentrations of acid or base, they have more corrosive to rubber. Rubber for the expansion of the corrosion performance, aging, low intensity, with a rubber lined butterfly valve, diaphragm use effects are worse in essence, rubber impatient corrosion. After the rubber lined diaphragm valve to improve the corrosion resistance of a good fluorine for the diaphragm, but the fluorine it stand up to the upper and lower diaphragm membrane folds were broken off, resulting in mechanical damage, shorter valve life. Now the best way to deal with special ball valve water, it can use to 5 ~ 8 years.
7, why use a hard shut-off valve should be closed
Shut-off valve required leakage the lower the better, soft-sealing valve leakage is the lowest cut off the effect is good, but not wear and poor reliability. From leakage and small, sealed double standards and reliable, soft sealing off sealing off the good as hard. Such as full-featured ultra-light valve, sealing the reactor with wear-resistant alloy protection, high reliability, leakage rate of 10 to 7, has been able to meet the requirements of cut off valves.