Overall dimensions and technical information are provided solely for informative purposes and may be modified without notice. A|6 Hydraulic circuit In some cases flow rate is measured in m /h which correspond a Kv measured To obtain Kv expressed in it is sufficient to multiply the Kv value expressed in B y the co efficient 1 6,66. The coefficient kv is perfectly suitable to express the flow rate of fluids but only gives approximate values in case of compressed air. Experiences gained in hydraulic environments can be inferred in the pneumatic field, bearing in mind the difference in density, and assuming that the air flow will generate the same pressure drops and flow reductions as water It is therefore possible to calculate reliable values for compressed air using flow coefficients Kv obtained from experiments with water. To define the flow rate Qn through a valve at a given constant absolute inlet pressure P1, regardless of fluctuations of the downstream absolute pressure P2, refer to the equation below: Equation [6] is real up to ΔP = therefore P2 = For lower P2 values the flow rate is considered to be constant, corresponding to the sonic flow rate Q*n given by the following equation: The nominal flow rate QNn The nominal flow rate is the flow volume (at normal conditions) that passes through a valve with an upstream pressure P1=6bar (7 bar absolute pressure) and a pressure drop of 1 bar, corresponding to a downstream relative pressure P2 of 5bar (6 bar absolute pressure). Normally the nominal flow rate is expressed in l/min and can be easily deduced from an experimental flow curve drawn for a upstream pressure of 6 bar (relative). Nominal flow rate can be useful for a preliminary assesment of the performances of different valves but in reality can be used only if the working conditions are the same as those mentioned before. In order to be able to compare valve charactersistics which are expressed in different coefficients it is possible to use conversion equations. Given the C and b coefficient, it is possible to determine the nominal flow rate using the following equation: Conversion table [6] [7] [8] where: is the flow rate in volume I/min; is the hydraulic coefficient is the absolute reference temperature; is the inlet absolute temperature in °K; is the downstream absolute pressure in bar; is the pressure drop P1 - P2 in bar. where: è in I/min e C in The correlation between the hydraulic coefficient KV and the corresponding nominal flow rate is as follows: where: è in I/min e KV in Qn Nominal flow rate Nl/min kv Hydraulic coefficient l/min Kv m3 /hours Cv USA gallons/min Sp Nominal inner section area mm2 dp2 Nominal diameter* mm2 *to calculate the diameter dp (mm2) square root of dp2 APPENDIX A Appendix Dimensioning Solutions for pneumatic automation General Catalogue
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