When selecting the control valve, the physical characteristics of the complete process fluid and the working conditions of the control valve, the composition of the main fluid, the temperature, the density, the viscosity, the normal flow rate, the maximum flow rate, the minimum flow rate, the maximum flow rate and the minimum flow rate Import and export pressure, the maximum pressure difference. In the technical aspects of the main control and determine the structure of the control valve itself, flow characteristics, rated flow coefficient Kv value, caliber size, process to allow pressure calculation and the implementation of the selection of institutions, materials and installation aspects.

Select the valve should generally follow the principles of the following points.

First, the structure of the control valve type: should be able to meet the media temperature, pressure, mobility, flow, adjust the scope and tightness requirements.

Second, the control valve flow characteristics: should be able to meet the system characteristics for reasonable compensation.

The Q-Qmax = f (l / L), where Q / Qmax is the relative flow rate, and the flow rate of the control valve is the relative flow rate between the relative flow of the medium and the stem relative displacement. The ratio of the flow Q to the full open flow Qmax at a certain opening, l / L is the relative displacement, and the ratio of the spool displacement l to the fully open displacement L at a certain opening.

The general principle of the selection is that the flow characteristics of the high pressure regulating valve should be opposite to the characteristics of the adjustment object and the characteristics of the regulator, which can make the integrated characteristic of the adjustment system close to linearity. The choice of flow characteristics is usually carried out at the request of the process system, but the following is also considered.

1, the linear flow characteristics of the scope of application: ① differential pressure change is small, almost constant; ② process changes in the main parameters of a linear; ③ system pressure loss is mostly allocated in the control valve (change the opening degree, Relatively small); ④ small external interference, a small change in the given value, adjustable range requirements. 2, the percentage of the characteristics of the scope of application: ① the actual adjustable range; ② opening change, the valve differential pressure change is relatively large; ③ pipeline system pressure loss; ④ process system load fluctuations; ⑤ control valve is often small Run under the opening.

3, in addition to the above two commonly used flow characteristics, there are parabolic characteristics and fast opening characteristics of other flow characteristics of the control valve.

Third, the control valve caliber: should be able to meet the requirements of the flow on the process. According to the known fluid conditions, calculate the necessary Kv value, select the appropriate control valve caliber.