What is the principle of caliber calculation?
In different automatic control systems, the flow, medium, pressure, temperature and other parameters vary greatly, and the flow coefficient of the control valve is tested under the pressure difference of 100KPA and the medium is normal temperature water. It is not possible to compare the actual flow with the flow coefficient of the valve (because of the different conditions of pressure difference and medium), but the value of C must be calculated. The actual parameters are brought into the corresponding C value calculation formula, and the C value is compared with the CZ value of the valve, so as to determine the valve diameter. Finally, relevant checking calculation should be carried out to further verify whether the selected valve can meet the working requirements.
What are the steps of regulating valve diameter calculation?
From the process to the final valve diameter determination, the following steps are generally required.
1、 Determine the use conditions.
1. The name, properties and main physicochemical parameters of the medium passed;
2. Understand the process parameters clearly;
3. Piping condition (pipe diameter before and after the valve, calculation of system resistance);
4. The type and characteristics of the controlled object;
5. Adjustment performance requirements, such as requirements for leakage and stability.
2、 Primary selection of valve type, and determine the flow characteristics and flow direction.
3、 Determination of calculated flow rate. According to the existing production capacity, equipment load and medium conditions, the maximum working flow Qmax and the minimum working flow qmin are determined.
4、 The decision to calculate the differential pressure. The s value is selected according to the characteristics of the system, and then the differential pressure is calculated.
5、 Kv value calculation. According to the calculated flow rate, calculated pressure difference and other relevant parameters, the kvmax of the maximum working flow which determines the regulating valve preliminarily is obtained.
6、 According to the calculated kvmax, the first gear Kv value larger than kvmax and close to kvmax is selected to obtain the caliber.
7、 Opening checking calculation.
8、 Actual adjustable ratio checking calculation. Generally, the actual adjustable ratio should be greater than 10.
9、 Pressure difference proofreading (only checking from the opening and adjustable ratio is not good, which may cause the valve to be closed and start, so this item is added).
10、 If the above checking calculation is qualified, the selected valve diameter is qualified. If it is not qualified, the caliber (and Kv value) shall be re determined or other valves shall be selected for re checking to be qualified.