Datasheet

Solenoid Valves Flow Characteristics
(How to indicate flow characteristics)
Front matter 1
1. Indication of flow characteristics
Indication of the flow characteristics in specifications for equipment such as a solenoid valve, etc. is depending on “Table (1)”.
2. Equipment for pneumatics
2.1 Indication according to the international standards
(1) Standards conforming to
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 characteristics
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 absolute upstream pressure and the density in the standard condition.
Critical pressure ratio
b
: Checked flow will occur when the pressure ratio (downstream pressure/upstream pressure)
is at or smaller than this value.
Choked flow : It is the flow in which the upstream pressure is higher than the downstream pressure and where
sonic speed is reached in a certain part of the equipment.
Gaseous mass flow rate is in proportion to the upstream pressure and not dependent on the
downstream pressure.
Subsonic flow : Flow when the pressure ratio is 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 abbreviation (ANR) after the unit depicting air volume.
(standard reference atmosphere)
Standard conforming to: ISO 8778: 1990 Pneumatic fluid power—Standard reference atmosphere,
JIS B 8393: 2000: Pneumatic fluid power—Standard reference atmosphere
(3) Formula of flow rate
It can be indicated by the practical unit 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
P
2
+ 0.1
———— – b
P
1
+ 0.1
Q
= 600 x
C
(
P
1
+ 0.1) 1 – —————— ———— ···························· (2)
1 – b
Q : Air flow rate [dm
3
/min (ANR)], the SI unit dm
3
(Cubic decimetre) is also allowed to be described by
l
(liter). 1 dm
3
= 1
l
.
2
293
273 +
t
Indication by
international standard
C , b
Other
indications
S
Cv
Cv
Standards conforming to
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 Characteristics
Av
Equipment for
controlling
process fluids
Equipment for
pneumatics
Corresponding
equipment
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