Datasheet

Front matter 3
Solenoid Valves Flow Characteristics
(How to indicate flow characteristics)
2.2 Effective area S
(1) Standards conforming to
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 characteristics
Effective area S : The flow ability of a component, represented by its equivalent "ideal" cross sectional area. This effective area is
calculated under sonic conditions by measuring pressure loss in an air tank. Like sonic conductance C , the
effective area is a method of expressing the flow rate of a product.
(3) Formula of 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
P
2
+ 0.1
———— > 0.5, subsonic flow
P1 + 0.1
293
Q = 240 x S ( P
2
+ 0.1) ( P
1
– P
2
) ————··············································(4)
273 +
t
Conversion with sonic conductance C :
S = 5.0 x C ·······································································································(5)
Q :Air flow rate[dm
3
/min(ANR)], the SI unit dm
3
(cubic decimetre) is also allowed to be described by
l
(litre)
S : Effective area [mm
2
]
P
1
: Upstream pressure [MPa]
P
2
: Downstream pressure [MPa]
t : Temperature [°C]
Note) Formula for subsonic flow (4) is only applicable when the critical pressure ratio b is unknown. It is the same as the formula
for sonic conductance
C (2) only when b =0.5
(4) Test method
Pipe the text equipment to the text circuit shown in Fig. (2). Fill the air tank with compressed air and keep the pressure at a
constant level above 0.6MPa (0.5MPa). Then discharge the air until the pressure in the tank drops to 0.25MPa (0.2MPa).
Measure the time required to dischargue the air and the residual pressure in the air tank after leaving it until the pressure
becomes stable in order to calculate the effective sectional area S by the following formula. Select the capacity of the air tank
according to the effective sectional area of the text equipment. In the case of JIS B 8373, 8374, 8375, 8379, 8381, the pressure
values are in parentheses and the coefficient of 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]
Air supply Filter
Shut off
valve
Pressure control
equipment
Thermometer
Pressure switch
Control
circuit
Pressure gauge
or
pressure converto
r
Timer (Clock)
Pressure recorder
Solenoid
valve
Power
supply
Equipment for test
Rectifier tube in the
downstream side
Rectifier tube in the
upstream side
Fig. (2) Test circuit based on JIS B 8390