Series VXD Solenoid Valve Flow-rate Characteristics (How to indicate flow-rate characteristics) 1. Indication of flow-rate characteristics The flow-rate characteristics in equipment such as a solenoid valve etc. are indicated in their specifications as shown in Table (1). 2. Pneumatic equipment 2.1 Indication according to the international standards (1) Conformed standard ISO 6358: 1989 : Pneumatic fluid power.Components using compressible fluids. Determination of flow-rate characteristics JIS B 8390: 2000 : Pneumatic fluid power.Components using compressible fluids. How to test flow-rate characteristics (2) Definition of flow-rate characteristics The flow-rate characteri stics are indicated as a result of a comparison between sonic conductance C and critical pressure ratiob. Sonic conductance C : Value which divides the passing mass flow rate of an equipment in a choked flow condition by the product of the upstream absolute pressure and the density in a standard condition. Critical pressure ratio b : Pressure ratio (downstream pressure/upstream pressure) which will turn to a choked flow when the value is smaller than this ratio. Choked flow : The flow in which the upstream pressure is higher than the downstream pressure and where sonic speed in a certain part of an equipment is reached. Gaseous mass flow rate is in proportion to the upstream pressure and not dependent on the downstream pressure. Subsonic flow : Flow greater than the critical pressure ratio Standard condition : Air in a temperature state of 20°C, absolute pressure 0.1 MPa (= 100 kPa = 1 bar), relative humidity 65%. It is stipulated by adding the “(ANR)” after the unit depicting air volume. (standard reference atmosphere) Conformed standard: ISO 8778: 1990 Pneumatic fluid power.Standard reference atmosphere, JIS B 8393: 2000: Pneumatic fluid power.Standard reference atmosphere (3) Formula for flow rate Described by the practical units as following. P2 + 0.1 When . b, choked flow P1 + 0.1 Q = 6 0 0 x C ( P 293 1 + 0 . 1 ) ……………………………………………(1) 273 + t P2 + 0.1 When > b, subsonic flow P1 + 0.1 P2 + 0.1 2 . b P1 + 0.1 293 Q = 600 x C (P1 + 0.1) 1 . …………………(2) 1 . b 273 + t Q: Air flow rate [dm3/min (ANR)], dm3 (Cubic decimeter) of SI unit are allowed to be described by L (liter). 1 dm3 = 1 L Corresponding equipment Pneumatic equipment Process fluid control equipment C, b . Av . . S Cv . Cv Conformed standard ISO 6358: 1989 JIS B 8390: 2000 IEC60534-2-3: 1997 JIS B 2005: 1995 Equipment: JIS B 8471, 8472, 8473 JIS B 8390: 2000 Equipment: JIS B 8373, 8374, 8375, 8379, 8381 ANSI/(NFPA)T3.21.3: 1990 Table (1) Indication of Flow-rate Characteristics Indication by international standard Other indications 140