Control ValveAs an indispensable piece of equipment in industrial production, many problems may be encountered from selection, use to maintenance. Here, I have collected some common problems, hoping to help you understand the control valve.

  1. What flow direction should be chosen forControl Valve? How to choose?

Single-seal control valves, such as single-seated control valves, high-pressure control valves and single-seal valves without balance holesSleeve control valvesneed to select the flow direction. Opening and closing flows have their own advantages and disadvantages. Open-flow control valves work relatively stably, but their self-cleaning performance and sealing performance are poor, and their service life is short; close-flow control valves have a long service life, good self-cleaning performance and sealing performance, but when the valve stem diameter is smaller than the valve core diameter, the stability is very poor.

Single-seated control valves, small-flow control valves and single-seal sleeve control valves usually choose open flow, and choose closed flow when serious flushing or self-cleaning is required, two-position quick-opening characteristicsControl ValveChoose the flow-closing type.

2. In addition to single-seated, double-seated and sleeve control valves, what other valves have regulating functions?

Diaphragm valves, butterfly valves, O-type ball valves (mainly globe valves), V-type ball valves (larger regulating ratio and shearing effect) and eccentric rotary valves are all valves with regulating functions.

3. Why can't double-sealControl Valvebe used as a shut-off valve?

The advantage of the double-seated control valve core is the force balance structure, which allows for a larger pressure difference. Its significant disadvantage is that the two sealing surfaces cannot be in good contact at the same time, resulting in a large leakage. If it is artificially and forcibly used in a shut-off occasion, it is obviously invalid, even if many improvements have been made to it (such as double sealingSleeve control valves), it is not recommended to do so.

4. Why is a double-seated control valve prone to swing when the opening is small?

For a single core, when the medium is open-flow type, the stability of the control valve is good; when the medium is closed type, the stability of the control valve is poor. A double-seated control valve has two slide valves, the lower slide valve is in the closed state, and the upper slide valve is in the open state. In this way, when working at a small opening, the flow-closing control valve core may cause valve vibration, which is why the double-seatedControl Valvecannot be used for small openings.

5. Why is the anti-clogging performance of a linear control valve poor, while that of an angle control valve is good?

LinearControl ValveThe slide valve is a vertical throttling valve, and the medium flows in and out horizontally. The flow path in the valve cavity will inevitably turn and reverse, which makes the flow path of the valve quite complex. In this way, there will be many dead zones, which provide space for the precipitation of the medium, and if the situation continues, it will cause blockage.

The throttling direction of the quarter-turn valve is horizontal, the medium flows in and out horizontally, and it is easy to take away dirty medium. At the same time, the flow path is simple, and the space for medium precipitation is small, so the angle stroke control valve has good anti-clogging performance.

6. Why has the sleeve control valve replaced the single-seated and double-seatedControl Valvebut has not been replaced?

       The sleeve control valve, which was introduced in the 1960s, was widely used at home and abroad in the 1970s, and the proportion of sleeve control valves was even larger in petrochemical plants introduced in the 1980s. At that time, many people believed that sleeve control valves could replace single-seated and double-seated control valves. However, this is not the case so far. Single-seated, double-seated andSleeve control valvesare used equally, because the sleeve control valve only improves the throttling form, stability and maintainability better than the single-seated control valve, but its weight, anti-clogging and leakage indicators are consistent with the single-seated and double-seated control valves. How can it replace the single-seated and double-seatedControl Valve? Therefore, they can only be used together.

7. Why is the stem of a linear control valve thinner?

This involves a simple mechanical principle: high sliding friction and low rolling friction. LinearControl ValveThe valve stem moves up and down, and the packing is slightly compressed, which will stack the valve stem very tightly, resulting in a larger hysteresis. Therefore, the valve stem is designed to be very small, and the packing uses packing with a small friction coefficient to reduce the gap. However, the problem is that the valve stem is thin, easy to bend and has a short service life. The solution to this problem is to use a stroke valve stem, that is, a quarter-turn valve, whose valve stem thickness is 2 to 3 times that of a linear valve stem, and it also uses long-life graphite packing and valve stem rigidity, long service life, small friction torque and small gap.