Overall dimensions and technical information are provided solely for informative purposes and may be modified without notice. A|7 Pipes flow resistence The C factor (l/sec) indicates the pipe flow capacity and is the ratio between the maximum flow rate and absolute pressure (ISO 6358). The flow capacity progressively decreases with increasing pipe length, due to the air friction on the pipe inner surface increasing the pressure drop. Therefore the longer the pipe the smaller the flow rate. The chart below shows the flow rate characteristics of different pipe sizes (i/d and o/d) in function of the length. Valve sizing The choice of the correct size valve is essential in order to ensure that the cylinder to be controlled will perform as expected. It is therefore necessary to know the cycle time to be achieved and to calculate the coefficient T which will be used as multiplier for the air consumption value previously calculated. The result of this equation, expressed in Nl/min and multiplied by a safety factor of 1.2, corresponds to the minimum flow rate needed (at standard conditions 6 bar supply and 5 bar on the consumption connection) to operate the cylinder at the required rate. T= 60 Qn = T x Consumption cycle time It is also imortant to ensure that the pipes used to connect the valve to the air supply and to the cylinder do not affect the flow rate in any way. The pipe inner bore must therefore be at least 1.5 times the diameter of the valve nominal orifice size. The choice of the fittings is also very important, the inner bore must be equal or greater than the pipe I/D. The diagram below shows the flow rate required to operate different size cylinders atvarying speeds and also the valve connection sizes. Flow rate in m3/ minute Diameter in inches Pressure loss expressed in Pa per 1mtr pipe length Valve working ports size Inlet flow rate (Nl/min) Cylinder speed (m/sec) APPENDIX A Appendix Dimensioning Solutions for pneumatic automation General Catalogue
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