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Fig. (1) Test circuit based on ISO 6358, JIS B 8390 od2 od1 3d3 . 10d3 10d1 3d1 10d2 3d2 od3 . 3d1 Pressure gauge or pressure convertor Differential pressure gauge or differential pressure converter Thermometer Flow control valve Pressure control equipment Pipe for measuring pressure in the downstream side Pipe for measuring pressure in the upstream side Equipment for test Pipe for measuring temperature Shut off Flow meter valve Air Filter supply C : Sonic conductance [dm3/(s・bar)] b : Critical pressure ratio [.] P1 : Upstream pressure [MPa] P2 : Downstream pressure [MPa] t : Temperature [°C] Note) Formula of subsonic flow is the elliptic analogous curve. Flowrate characteristics are shown in Graph (1) For details, please make use of SMC’s “Energy Saving Program”. Example) Obtain the air flow rate for P1 = 0.4 [MPa], P2 = 0.3 [MPa], t = 20 [°C] when a solenoid valve is performed in C = 2 [dm3/(s・bar)] and b = 0.3. 293 According to formula 1, the maximum flow rate = 600 x 2 x (0.4 + 0.1) x ..... = 600 [dm3/min (ANR)] 273 + 20 0.3 + 0.1 Pressure ratio = ..... = 0.8 0.4 + 0.1 Based on Graph (1), the flow rate will be 0.7 when the pressure ratio is 0.8 and b = 0.3. Hence, flow rate = Maximum flow rate x flow rate ratio = 600 x 0.7 = 420 [dm3/min (ANR)] (4) Test method Attach a test equipment with the test circuit shown in Fig. (1) while maintaining the upstream pressure to a certain level which does not go below 0.3 MPa. Next, measure the maximum flow to be saturated in the first place, then measure this flow rate at 80%, 60%, 40%, 20% and the upstream and downstream pressure. And then, obtain the sonic conductance C from this maximum flow rate. Besides that, substitute each data of others for the subsonic flow formula to find b, then obtain the critical pressure ratio b from that average. 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Equipment C, b P2 Q P1 b = 0.1 0.2 0.5 0.6 0.3 0.4 Pressure ratio (P2 + 0.1) / (P1 + 0.1) Graph (1) Flowrate characteristics Flow rate ratio 32 Series VXZ 