When selecting the regulating valve, firstly collect the complete physical parameters of the process fluid and the working conditions of the regulating valve. The main fluid composition, temperature, density, viscosity, normal flow, maximum flow, minimum flow, maximum flow and minimum flow Import and export pressure, maximum pressure difference and so on. In terms of technology, it mainly grasps and determines the structure of the valve itself, its flow characteristics, the rated flow coefficient Kv, the size of the bore, the calculation of the allowable differential pressure of the process, and the selection of actuators, materials, and installation.
The following principles should generally be followed when selecting a regulating valve.
The structure type of a regulating valve: It should be able to meet the requirements of medium temperature, pressure, fluidity, flow direction, adjustment range and tightness.
The flow characteristics of the two control valves: should be able to meet the system characteristics for reasonable compensation.
The flow characteristic of the regulating valve refers to the relationship between the relative flow of the medium flowing through the valve and the relative displacement of the valve stem. The mathematical expression is as follows: Q/Qmax=f(l/L), where Q/Qmax is the relative flow, which is the adjustment The ratio of flow Q to full open flow Qmax at a certain opening; l/L is relative displacement, and the ratio of valve displacement l to full open displacement L at a certain opening of the regulating valve.
The overall principle of selection is that the flow characteristics of the regulating valve should be opposite to those of the regulating object and the regulator, so that the overall characteristics of the regulating system can be made nearly linear. Selecting the flow characteristics is usually performed under the requirements of the process system, but the following actual conditions must also be considered.
1. Application of linear flow characteristics: 1 Little difference in differential pressure, almost constant; 2 The main parameters of the process flow change linearly; 3 The pressure loss of the system is mostly distributed on the regulating valve (change in opening, differential pressure on the valve Relatively small); 4 small external disturbances, small changes in the given value, small adjustable range requirements.
2. Equal percentage characteristics Applicable range: 1 Actual adjustable range is large; 2 Change in opening degree, the pressure difference on the valve is relatively large; 3 The pressure loss in the pipeline system is large; 4 The process system load fluctuates greatly; 5 The regulating valve is often small Run under the opening degree.
3. In addition to the above two commonly used flow characteristics, there are Other flow characteristics such as parabolic characteristics and quick opening characteristics.
The caliber of the three control valves: should be able to meet the flow requirements of the process.
According to the known fluid conditions, calculate the necessary Kv value and select the appropriate valve diameter.
The following principles should generally be followed when selecting a regulating valve.
The structure type of a regulating valve: It should be able to meet the requirements of medium temperature, pressure, fluidity, flow direction, adjustment range and tightness.
The flow characteristics of the two control valves: should be able to meet the system characteristics for reasonable compensation.
The flow characteristic of the regulating valve refers to the relationship between the relative flow of the medium flowing through the valve and the relative displacement of the valve stem. The mathematical expression is as follows: Q/Qmax=f(l/L), where Q/Qmax is the relative flow, which is the adjustment The ratio of flow Q to full open flow Qmax at a certain opening; l/L is relative displacement, and the ratio of valve displacement l to full open displacement L at a certain opening of the regulating valve.
The overall principle of selection is that the flow characteristics of the regulating valve should be opposite to those of the regulating object and the regulator, so that the overall characteristics of the regulating system can be made nearly linear. Selecting the flow characteristics is usually performed under the requirements of the process system, but the following actual conditions must also be considered.
1. Application of linear flow characteristics: 1 Little difference in differential pressure, almost constant; 2 The main parameters of the process flow change linearly; 3 The pressure loss of the system is mostly distributed on the regulating valve (change in opening, differential pressure on the valve Relatively small); 4 small external disturbances, small changes in the given value, small adjustable range requirements.
2. Equal percentage characteristics Applicable range: 1 Actual adjustable range is large; 2 Change in opening degree, the pressure difference on the valve is relatively large; 3 The pressure loss in the pipeline system is large; 4 The process system load fluctuates greatly; 5 The regulating valve is often small Run under the opening degree.
3. In addition to the above two commonly used flow characteristics, there are Other flow characteristics such as parabolic characteristics and quick opening characteristics.
The caliber of the three control valves: should be able to meet the flow requirements of the process.
According to the known fluid conditions, calculate the necessary Kv value and select the appropriate valve diameter.
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