Datasheet

Series VXZ
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 characteristics are indicated as a result of a comparison between sonic conductance C and
critical pressure ratio b.
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
It is described by the practical units as following.
When
P2 + 0.1
————
≤ b, choked flow
P1 + 0.1
293
Q = 600 x C (P1 + 0.1) ———— ·····························································(1)
273 + t
When
P2 + 0.1
———— > b, subsonic flow
P1 + 0.1
Q : Air flow rate [dm
3
/min (ANR)], dm
3
(Cubic decimetre) of SI unit are also allowed to be described by L (litre).
1 dm
3
= 1 L
P2 + 0.1
———— – b
P1 + 0.1
Q = 600 x C (P1 + 0.1) 1 – —————— ———— ···························· (2)
1 – b
2
293
273 + t
Solenoid Valve Flow-rate Characteristics
(How to indicate flow-rate characteristics)
C, b
Indication by
international standard
S
Cv
Cv
Conformed standard
ISO 6358: 1989
JIS B 8390: 2000
JIS B 8390: 2000
Equipment: JIS B 8373, 8374, 8375, 8379, 8381
IEC60534-2-3: 1997
JIS B 2005: 1995
Equipment: JIS B 8471, 8472, 8473
ANSI/(NFPA)T3.21.3: 1990
Table (1) Indication of Flow-rate Characteristics
Av
—
—
—
—
Pneumatic
equipment
Process fluid
control
equipment
Corresponding
equipment
Other
indications
29