Valve 10 common Why and the corresponding solutions

Why shut-off valve should use a hard seal?

Cut off valve requirements, soft-sealing valve leakage is the lowest leakage as low as possible, cut off the effect, but does not wear, poor reliability. Leakage is small, sealed and reliable double standards, soft sealing off as hard sealing off. Such as full-featured ultra-light valve, sealing the reactor with the protection of wear-resistant alloy, high reliability, leakage rate of 10-7, has been able to meet the requirements of the shut-off valve.

Why the double seal valves can not be used as shut-off valve to use?

The two-seat valve spool force balance the advantages structure, allowing a large pressure difference, and it highlights the shortcomings of the two sealing surface can not be a good contact, causing a large leak. It artificially mandatory for cutting off occasion, obviously not good, even if it made many improvements (such as double-sealed sleeve valve), is also undesirable.

Why the small opening of the seat valve is easy to oscillation?

Single - core, when the medium is open - type flow valve stability; when the medium is the flow of closed type, the stability of the valve. Seat valve spool, under the spool in the flow of closed, the valve in the open flow in the small opening, the flow of closed spool is easy to cause vibration of the valve, which is double seat valves can not be used for the reason of the small opening.

. Straight trip valve attempts to prevent the poor performance of the rotary valve attempts to prevent the performance?

Straight travel valve spool is a vertical throttle, while the medium is the level of flow into the outflow valve cavity flow must turn back street, so that the valve flow path becomes quite complex (such as the shape inverted "S" type). In this way, there are many dead, provide space for the precipitation of the medium run, causing blockage. Throttle valve angle direction is the horizontal direction, the medium level of flows into the level of outflow, easy medium is not clean away, while the flow path is simple medium precipitation space, so the rotary valve attempts to prevent the performance.

Why straight travel valve stem smaller?

Straight stroke adjustment valve it involves a simple mechanical principle: sliding friction, rolling friction. Linear actuator valve stem up and down movement, packing slightly compressed that it will stem a very tight package, resulting in a greater backlash. Stem design are very small, another commonly used filler friction coefficient of PTFE packing, in order to reduce hysteresis, which sent the stem, is easily bent, packing too short life. Solve this problem, the best way is to turn valve stem with a tour, rotary type control valve, its stem stroke than a straight stem crude 2 to 3 times, and use long life of graphite packing, stem stiffness Good, filling long life friction torque but small hysteresis small.

6. Why the rotary type valve to cut off the pressure difference?

The rotary type valve differential pressure cut off is because the media in the spool or the valve on a board together on the shaft torque is very small, so it can withstand greater pressure.

Why sleeve valves instead of the single seat valve has not happened yet?

1960s, the advent of the sleeve valve, both at home and abroad in the 1970s large-scale use, 80 years the introduction of petrochemical plants in the sleeve valve, the proportion that time, many people think the sleeve valve can replace the single, two-seater valve, a second-generation products. Now, is not the case, a single seat valve, double seat valves, sleeve valves have been the same use. This is because the sleeve valve has only improved throttle form of stability and safeguard a single seat valve, but its weight, attempts to prevent leakage targets with a single seat valve, how can it replace a single seat valve ? Therefore, it can only be used in conjunction.

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 of the rubber. Rubber corrosion performance for the expansion of aging, low intensity, rubber lined butterfly valves, diaphragm valves are poor, its essence is rubber impatient corrosion. Rubber lined diaphragm to improve the corrosion resistance good lined diaphragm, the diaphragm lined diaphragm stand up to the upper and lower folding was broken off, resulting in mechanical damage, the shorter the life of the valve. The best way is to water treatment with special ball valve, it can use to 5-8 years.

Why in the pneumatic valve piston actuator will be more and more?

For the pneumatic valve, the piston actuator can take full advantage of the gas supply pressure, the executive body size is smaller than the thin film, a greater thrust in the piston O-ring is more reliable than film, so its use will become increasingly and more.

10 why the selection is more important than the calculated?

Calculation and selection of comparison, the selection should be much more important, much more complex. Because the calculation is a simple formula, it is not the accuracy of the formula and process parameters is given is accurate. Selection related to the contents of more, a little careless, would lead to improper selection, not only cause a waste of manpower, material and financial resources, and the use of the effect is not ideal, bringing the number of use, such as reliability, life, running quality.

keywords: Spool, cut off valves, seat valves, open,