Overall dimensions and technical information are provided solely for informative purposes and may be modified without notice. A|5 VALVE UNDER TEST The experimental determination of the valve coefficient C & b is carried out with compressed air following standardised procedures and according to the scheme below. CETOP test circuit A Compressed air generator. B Pressure regulator to set upstream pressure P1. C Shut off valve. D Temperature sensor to check upstream temperature t 1, positioned in a low velocity area. E Pipe where the upstream pressure is measured. F Test valve. G Pipe where the downstream pressure is measured. H Flow regulator to adjust the downstream pressure P2. L Flow meter. M1,M2 Pressure measuring equipment for upstream and downstream. MΔP Pressure drop measuring equipment assuming P1-P2< 1 bar. Pipes E & G, used to measure the valve upstream and downstream pressure, must be sized according to the standard’s specifications and change in size depending on the valve port sizes; the position of the connection at which the measurements are taken depends on the pipe’s inner diameter. Conductance C is determined with the following equation, measuring the critical flow rate Q* through the valve, where upstream pressure P1 is constant and greater than 3 bar. HYDRAULIC COEFFICIENT KV The hydraulic coefficient allows, using the equation. The calculation of the flow rate of a fluid through a valve. Considering a given constant pressure P1 it is necessary to proceed measuring the flow rate Q' corresponding to a pressure drop DP = P1-P2 = 1 bar. Equation 3 is used to calculate the critical ratio as it is difficult to experimentally identify the exact pressure P*2 at which the flow becomes sonic. The values of both the conductance C and the critical ratio b are experimentally calculated and are the average of the results obtained. Equation [1] is used to calculate the flow in subsonic conditions P2>b·P1 when values C ; b and the valve working conditions (P1, P2, T1) are known. Under sonic conditions , P2£ b · P1 the equation can be simplified and the maximum flow rate can be calculated as follows: Q* = C · P1 · kt Using these measurement units the flow rate coefficient Kv represents the flow rate (in liters) of water across the valve with a pressure drop of 1 bar. The measurement are carried out using the standardised circuit below on which the connection ports are positioned according to the pipe inner bore size (norm VDE/VDI 2173). Pressure critical ration b can be calculated using the following equation: [2] [3] [4] [5] where: is the fluid flow rate in l/min is the pressure drop inside the valve calculated in bar (P1 - P1) is the fluid density calculated in Kg/dm³ is the hydraulic coefficient calculated in APPENDIX A Appendix Dimensioning Solutions for pneumatic automation General Catalogue
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