The Basic Knowledge of Regulating Valve Selection and Control

Selection of regulating valve. At first, you need to collect complete physical parameters and control valve operating conditions. The main fluid compositions are temperature, density, viscosity, normal flow, maximum flow, minimum flow, maximum flow and minimum flow Import and export pressure, the maximum pressure and so on. In the technical aspects, we need to grasp and determine the valve body’s structure, flow characteristics, rated flow coefficient KV value, caliber size, pressure difference calculation and the choice of implementing agencies, materials and installation and other aspects.

Selection of the regulating valve should generally follow the following principles :

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

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

The flow characteristic of regulating valve means the relationship between relative flow of medium and the relative moving of stem , and its mathematical expression is Q / Qmax = f (l / L), Q / is the relative flow rate, Q is the regulation of the relative flow and Qmax is full opening flow rate; l / L is the relative displacement, l is the displacement of a certain opening of the regulating valve, L is the full opening displacement.

The general principle of selection is that the flow characteristics of the high pressure regulating valve should be opposite to the characteristics of the regulated object and the characteristics of the regulator, so that the comprehensive characteristic of the regulating system is close to linear. The choice of flow characteristics is usually carried out at the request of the process system, but also need to consider the the following actual situation.

1, the application scope of the linear flow characteristic: ① Little change of different pressure , almost constant; ②The main parameters of the process change is linear; ③Loss of the system pressure is allocated to regulating valve (with opening change, the valve on the differential pressure is relatively small); ④ external interference is small, reference value is small changes, adjustable range requirements is somal.

2, equal percentage of the application scope: ① the actual adjustable range is large; ② opening changes, t the different pressure of valve is relatively large; ③ Loss of piping system pressure is large; ④ Process system loads large fluctuations; ⑤ Regulating valve is often small opening.

3, In addition to the above two kinds of commonly used flow characteristics, there are parabolic characteristics and fast opening characteristics of regulating valve flow characteristics.

Third, the caliber of the valve: It should be able to meet the process on the flow requirements. According to the known fluid conditions, you have to calculate the necessary KV value, and select the appropriate regulating valve caliber.

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