Calculation formula of flow coefficient of regulating valve

The flow coefficient Kv of the regulating valve is an important parameter of the regulating valve, which reflects the ability of the regulating valve to pass the fluid, that is, the capacity of the regulating valve. According to the calculation of the flow coefficient Kv of the regulating valve, the diameter of the regulating valve can be determined. In order to correctly select the caliber of the regulating valve, the Kv value of the rated flow coefficient of the regulating valve must be correctly calculated. The definition of the rated flow coefficient Kv of the regulating valve is: under the specified conditions, that is, the pressure difference between the two ends of the valve is 10Pa, the density of the fluid is lg/cm, and the flow through the regulating valve is m/h or t/h at the rated stroke. number. 1. Calculation of Kv value of general liquid a. Non-blocking flow discriminant: △P Calculation formula: Kvu003d10QL In the formula: FL-pressure recovery coefficient, see attached table FF-fluid critical pressure ratio coefficient, FFu003d0.96-0.28 PV - At the valve inlet temperature, the saturated vapor pressure of the medium (absolute pressure), kPa PC-fluid thermodynamic critical pressure (absolute pressure), kPa QL-liquid flow m/h ρ-liquid density g/cm Pressure) kPa P2-post-valve pressure (absolute pressure) kPa b. Blocking flow discriminant: △PFL (P1-FFPV) Calculation formula: Kvu003d10QL In the formula: the meaning and unit of each character are the same as the previous 2. Calculation of Kv value of gas a. General gas when P2>0.5P1, when P2≤0.5P1 In the formula: Qg-gas flow Nm/h in standard state Pm-(P1+P2)/2(P1, P2 are absolute pressure) kPa △Pu003d P1-P2 G - specific gravity of gas (air Gu003d1) t - gas temperature ℃ b. High pressure gas (PN>10MPa) When P2>0.5P1, when P2≤0.5P1 In the formula: Z-gas compressibility, you can check GB/T 2624-81 'Design, Installation and Use of Flow Measurement Throttling Device' 3. Low Reynolds Number Correction (Calculation of KV Value of High Viscosity Liquid) When the liquid viscosity is too high or the flow rate is too low, due to the decrease of Reynolds number, the change The flow state of the fluid flowing through the regulating valve is in a low-velocity laminar flow when Rev<2300, so the KV value calculated according to the original formula has a large error and must be corrected. At this time, the calculation formula should be: In the formula: Φ-viscosity correction coefficient, obtained from Rev check FR-Rev curve; QL-liquid flow m/h For single-seat valve, sleeve valve, angle valve, etc. with only one flow path For valves with two parallel flow paths such as double-seat valves and butterfly valves: Kv′—the flow rate calculated without considering viscosity correction ν—fluid kinematic viscosity mm/s FR-Rev relationship curve FR-Rev relationship Figure 4 .Calculation of Kv value of water vapor a. When P2>0.5P1 for saturated steam, when P2≤0.5P1 In the formula: G-steam flow kg/h, the meanings and units of P1 and P2 are the same as before, K-steam correction coefficient, The K values u200bu200bof some steam are as follows: water steam: Ku003d19.4; ammonia steam: Ku003d25; Freon 11: Ku003d68.5; methane, ethylene steam: Ku003d37; propane, propylene steam: Ku003d41.5; butane, Isobutane vapor: Ku003d43.5. b. Superheated water steam When P2>0.5P1 When P2≤0.5P1 In the formula: △t—the degree of superheat of steam in °C, the meanings and units of Gs, P1, and P2 are the same as before.
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