Datasheet
C : Sonic conductance [dm
3
/(s·bar)]
b : Critical pressure ratio [—]
P1 : Upstream pressure [MPa]
P2 : Downstream pressure [MPa]
t : Temperature [°C]
Note) Formula of subsonic flow is the elliptic analogous curve.
Flow-rate characteristics are shown in Graph (1) For details, please make use of SMC’s “Energy Saving Program”.
Example)
Obtain the air flow rate for P1 = 0.4 [MPa], P2 = 0.3 [MPa], t = 20 [°C] when a solenoid valve is performed in
C = 2 [dm
3
/(s·bar)] and b = 0.3.
According to formula (1), the maximum flow rate = 600 x 2 x (0.4 + 0.1) x = 600 [dm
3
/min (ANR)]
Pressure ratio = = 0.8
Based on Graph (1), the flow rate ratio will be 0.7 when the pressure ratio is 0.8 and b = 0.3.
Therefore, flow rate = Maximum flow rate x flow rate ratio = 600 x 0.7 = 420 [dm
3
/min(ANR)]
(4) Test method
Attach a test equipment with the test circuit shown in Fig. (1) while maintaining the upstream pressure to a
certain level which does not go below 0.3 MPa. Next, measure the maximum flow to be saturated in the first
place, then measure this flow rate at 80%, 60%, 40%, 20% and the upstream and downstream pressure. And
then, obtain the sonic conductance C from this maximum flow rate. Besides that, substitute each data of
others for the subsonic flow formula to find b, then obtain the critical pressure ratio b from that average.
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Flow rate ratio
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Equipment
C, b
P2
Q
P1
b = 0.1
0.2
0.5
0.6
0.3
0.4
Pressure ratio (
P2 + 0.1) / (P1 + 0.1)
Graph (1) Flow-rate characteristics
Fig. (1) Test circuit based on ISO 6358, JIS B 8390
ød2
ød1
3d3
3d210d23d1
10d1
≥ 10d3
ød3 ≥ 3d1
Pressure gauge or
pressure convertor
Differential pressure gauge or
differential pressure converter
Thermometer
Flow control
valve
Pressure control
equipment
Pipe for
measuring
pressure in the
downstream side
Pipe for
measuring
pressure in the
upstream side
Equipment
for test
Pipe for measuring
temperature
Flow meter
Shut off
valve
FilterAir
supply
Solenoid Valve Flow-rate Characteristics
Series VX21/22/23
273 + 20
293
0.3 + 0.1
0.4 + 0.1
31