Datasheet
2.2 Effective area S
(1) Conformed standard
JIS B 8390: 2000: Pneumatic fluid power—Components using compressible fluids—
Determination of flow rate characteristics
Equipment standards: JIS B 8373: 2 port solenoid valve for pneumatics
JIS B 8374: 3 port solenoid valve for pneumatics
JIS B 8375: 4 port, 5 port solenoid valve for pneumatics
JIS B 8379: Silencer for pneumatics
JIS B 8381: Fittings of flexible joint for pneumatics
(2) Definition of flow-rate characteristics
Effective area S
:
The cross-sectional area having an ideal throttle without friction deduced from the calcula-
tion of the pressure changes inside an air tank or without reduced flow when discharging
the compressed air in a choked flow, from an equipment attached to the air tank. This is the
same concept representing the “easy to run through” as sonic conductance C.
(3) Formula for flow rate
When
P2 + 0.1
———— ≤ 0.5, choked flow
P1 + 0.1
293
Q = 120 x S (P1 + 0.1) ————
··································································(3)
273 + t
When
P2 + 0.1
———— > 0.5, subsonic flow
P1 + 0.1
293
Q = 240 x S (P2 + 0.1) (P1 – P2) ————
··············································(4)
273 + t
Conversion with sonic conductance C :
S = 5.0 x C·······································································································(5)
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
S
: Effective area [mm
2
]
P1 : Upstream pressure [MPa]
P2 : Downstream pressure [MPa]
t
: Temperature [°C]
Note) Formula for subsonic flow (4) is only applicable when the critical pressure ratio b is the unknown
equipment. In the formula (2) by the sonic conductance C, it is the same formula as when b = 0.5.
(4) Test method
Attach a test equipment with the test circuit shown in Fig. (2) in order to discharge air into the atmosphere
until the pressure inside the air tank goes down to 0.25 MPa (0.2 MPa) from an air tank filled with the
compressed air at a certain pressure level (0.5 MPa) which does not go below 0.6 MPa. At this time, measure
the discharging time and the residual pressure inside the air tank which had been left until it turned to be the
normal values to determine the effective area S, using the following formula. The volume of an air tank should
be selected within the specified range by corresponding to the effective area of an equipment for test. In the
case of JIS B 8373, 8374, 8375, 8379, 8381, the pressure values are in parentheses and the coefficient of the
formula is 12.9.
V Ps + 0.1 293
S = 12.1 — log10 (—————) —— ·················(6)
t P + 0.1
T
S
: Effective area [mm
2
]
V
: Air tank capacity [dm
3
]
t
: Discharging time [s]
Ps
: Pressure inside air tank
before discharging [MPa]
P
: Residual pressure inside air tank
after discharging [MPa]
T
: Temperature inside air tank
before discharging [K]
Rectifier tube on the
downstream side
Rectifier tube on the
upstream side
Fig. (2) Test circuit based on JIS B 8390
Pressure switch
Power
supply
Solenoid
valve
Equipment
for test
Pressure gauge
or pressure
convertor
Timer (Clock)
Pressure recorder
Control
circuit
Thermometer
Air tank
Pressure control
equipment
Shut off
valve
FilterAir
supply
Solenoid Valve Flow-rate Characteristics
Series VXZ
31