Pneumatic Clean Series

257Flow Characteristics of Solenoid Valve(How to Express Flow Characteristics)1. Express of Flow CharacteristicsTable 1 shows the applicable International designation of flowcharacteristics in the specificatoin section of a solenoid valve orany other types of equipment.Table 1EquipmentPneumaticsequipment2. Pneumatic Equipment2-1 Calculating flow rate according to International Standards(1)Flow rate calculation formulaThe flow rate calculation formula is defined as follows:IfP2+0.1———— ≤ b, a choke flow results.P1+0.1293Q=600XC(P1+0.1) ———273+tIfDesignation of flow characteristicsDesignationbased oninternationalstandardsC, bOtherdesignationSCvP2+0.1———— > b, a subsonic flow results.P1+0.1Applicable standardsISO 6358: 1989JIS B 8390: 2000JIS B 8390: 2000Equipment: JIS B 8373, 8374, 8375, 8379, 8381ANSI/(NFPA)T3.21.3: 19902P2+0.1———— bP1+0.1 293Q=600XC (P1+0.1) 1 – ————— ——–—1 – b 273+tQ : Air flow rate [dm 3 /min(ANR)].The dm 3 (cubic decimeter) in the SI system may be expressedby L(liter). 1dm 3 =1L.Standard condition: Air under condition temperature 20°C,absolute pressure 0.1MPa (=100kPa=1bar), relative humidity65%.C: Sonic conductance [dm 3 /(s·bar)]b: Critical pressure ratio [-]P1: Upstream pressure [MPa]P2: Downstream pressure [MPa]t: Temperature [°C]Note) The formula for subsonic flow is that of an elliptic approximatecurve.Figure 1 is the flow characteristic diagram. For more information,please see Energy Saving Programs by SMC.Flow rate10.90.80.70.60.50.40.30.20.10P1b=0.10.20.3EquipmentC, b0.4P20 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1Figure 1QPressure rate (P2+0.1)/(P1+0.1)Flow rate characteristic diagram0.50.6(2) Test methodPipe the test equipment to the test circuit shown in Figure 2.Keep the upstream pressure at a certain constant level above0.3MPa. First measure the maximum flow rate in saturation.Then, measure the flow rate, upstream pressure anddownstream pressure each at 80%, 60%, 40% and 20%points of the flow rate. Calculate the sonic conductance Cfrom the maximum flow rate. Also, substitute other data forvariables in the formula for sobsonic flow and obtain thecritical pressure rate b by averaging the critical pressure ratesat those points.AirsupplyPressure controlequipmentFilterShut-offvalveød3≥3d1Pressure gauge orpressure transducerTemparaturegauge3d3ød1≥10d3 10d1 3d1 10d2Differential pressure gauge ordifferential pressure transducerFlow controlvalve3d2Flow meterThermometric pipe Test equipmentUpstream pressuremeasuring tubeDownstream pressuremeasuring tubeød2Figure 2 Test circuit of ISO 6358 and JIS B 8390238