The control valve is one of the types of fittings that finds the widest application in various industries. This device can be used as a simple temperature controller or as part of a complex process control system in automatic mode. Regardless of these factors, the selection of such a valve is a very important point.
If the control valve is properly sized, not only will optimal control accuracy be achieved, but problems such as erosive wear and high noise levels will be easily avoided. In some cases, the valve has a capacity that is fully consistent with the task being solved, and in order to reduce noise levels, it is worth giving preference to valve types with a larger nominal diameter.
The control valve is quite difficult to select due tothat it is necessary to link together a number of requirements, which, in fact, are mutually exclusive. Selecting a valve with little or too much capacity can cause significant problems. If the control valve has too large capacity, then this leads to the fact that it does not provide the proper level of control accuracy. This is due to the fact that the valve stem will move a small distance (noticeably less in comparison with the full stroke of the stem). Errors of this kind often lead to instability of the entire system, as well as to the failure of both the valve itself and the entire actuator. Sometimes the control valve is selected so that the pressure drop across the open device is the maximum for that particular application at the highest steam flow rate. In practice, this means that the selection of the valve is carried out for differential pressure.
An important parameter to be guided by when choosing a control valve is noise. The valve should be selected so that the steam flow rate at the outlet does not exceed 30% of the speed of sound. This parameter is exceeded very often due to the fact that the nominal diameter of the valve is very small, while the seat has a large capacity. The shut-off and control valve may have a special design that can significantly reduce the noise level. In such units, the saddle-plunger pair is presented in the form of perforated cylinders, which significantly reduces the levelnoise and also reduces cavitation (if the valve is used on a liquid).
The choice of a valve, as it became clear, must be carried out with the obligatory consideration of a considerable set of factors, which significantly complicates this process. The surest way to avoid any problems is to contact a reliable supplier with a sufficient level of knowledge as well as experience. This will allow him to offer the client the highest quality products. It is important to pay attention to certain points, among which it is worth highlighting: the reputation of the manufacturer, the suitability of the valve for repair, the possibility of changing the capacity or characteristics of the valve, as well as other parameters that affect usability.
