I would like to ask about the diameter of the control valve

The sizes are all calculated; they’re not simply reduced by one or two sizes. It’s normal for different manufacturers to use different values – 80% is a bit large

The size of the valve is not related to the pipes; it depends on the operating conditions, such as the density, pressure, viscosity, pressure difference, and temperature of the medium. By calculating the KV value, an appropriate valve can be selected

The size of a control valve has no direct relationship with the size of the pipeline; it can be slightly smaller or the same size. Specifically, each control valve manufacturer is responsible for calculating the diameter of the valve core. At normal flow rates, an opening degree of 80% is a bit high, but this isn’t absolute – it depends on how much the maximum flow rate allowed by your process conditions differs from the normal flow rate.

1. When designing the diameter of a control valve, is it generally necessary to choose a size that is one or two sizes smaller than that of the pipe, but still not smaller than the pipe’s standard diameter? Why is it designed this way? Is there a regulatory basis? →Under normal circumstances, your understanding is correct. Generally, the reduction in diameter is limited to two stages, and it cannot be less than half; there are regulatory guidelines for this. It is also for the sake of pipeline stress considerations. As for the reduction in diameter, factors such as the cost of purchasing valves and issues related to adjustment quality need to be taken into account. That’s your second question: when the diameter is larger, the opening remains at a low level throughout operation, and the quality of adjustment is not good. 2. For the data sheets provided by the design institute, do different manufacturers arrive at the same valve diameter after performing calculations? (This project used an unknown brand of control valve; the diameter specified by the manufacturer for this valve was actually the same as that of the pipe. Moreover, at normal flow rates, the valve reached an opening degree of 80%. With the FISHER valves used in the past, such a situation never occurred – the valve diameters were always smaller than those of the pipes, and the opening degrees were not as high.) . . ) → The internal design of valves from different manufacturers can vary; even if they are all single-seat valves with the same diameter, there will still be differences. Compared to domestic valves of the same size, FISHER has a higher CV value than those from other valve manufacturers. Note: Adjusting valves from small workshops should be used with caution.

When selecting a control valve, there is no inherent relationship with the pipe diameter. Generally, we prefer to use valves with the same diameter as the pipeline, and then determine the valve opening based on the pressure difference before and after the valve as well as the flow rate under operating conditions. If the required opening is too small, we choose a valve with a slightly smaller diameter and recalculate; if the opening exceeds 80%, we consider increasing the diameter or altering the regulation characteristics of the valve core.

The characteristics of a control valve are primarily determined by the valve core, valve seat, and actuator. As long as the valve housing does not affect the proper functioning of the valve core and seat (it cannot be smaller than the diameter of the seat), its size is only related to price. Typically, the effective bore of a control valve (the diameter of the valve disc) is smaller than the pipe size; therefore, it is common for the valve opening diameter to be smaller than that of the pipe. If FISHER’s valve is not used with its default diameter and a larger connection size is required, it will weld a reducer at each end and sell it to you at a special order price.