Select the control valve, the first to collect the complete process of the physical parameters of the fluid and regulating valve working conditions, the main fluid composition, temperature, density, viscosity, normal flow, maximum flow, minimum flow, maximum flow and minimum flow under the import and export pressure, the maximum pressure and poor. And in the technical aspects of the main grasp and determine the structure of the valve itself, flow characteristics, the nominal flow coefficient kv value, caliber size, process tolerance calculation and the implementation of the selection of the organization, materials and installation and other aspects of the content.

The principle of selecting the regulating valve should follow the following points.

I. The structure of the regulating valve should be able to meet the requirements of medium temperature, pressure, fluidity, flow direction, adjustment range and tightness.

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

The flow characteristic of the regulating valve refers to the relation between the relative flow of the valve and the relative displacement of the stem, the mathematical expression is as follows: Q/qmax=f (L), the Q/qmax is relative flow, the ratio of flow Q to open flow Qmax in a certain opening degree; L is relative displacement, The ratio of valve core displacement L to open displacement l at a certain opening.

The overall principle of the selection is that the flow characteristics of the high-pressure regulating valve should be opposite to that of the regulating object and the regulator, so that the comprehensive characteristic of the regulation system is close to the linearity. The selection of flow characteristics is usually carried out under the process system requirements, but the following realities are also considered.

1, linear flow characteristics of the scope of application: The variation of ① differential pressure is small and almost constant; the main parameters of ② process are linear; ③ system pressure loss is mostly allocated on the regulating valve (change the opening, the valve on the differential pressure is relatively small); ④ external interference small, the given value change small, adjustable range requirements small. 2, such as the scope of the application of the range: ① actual adjustable range, the change of ② open, valve pressure change is relatively large, ③ piping system pressure loss, ④ process system load fluctuation;

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, adjust the caliber of the valve: should be able to meet the process of flow requirements. br/> calculates the necessary KV value according to the known fluid condition, and chooses the appropriate regulating valve caliber.