Datasheet

Front matter 2
Solenoid Valves Flow Characteristics
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 characteristics curve is indicated in the Graph (1) For details, please use SMC’s “Energy Saving Program”.
Example)
Obtain the air flow rate when P1 = 0.4 [MPa], P 2 = 0.3 [MPa], t = 20 [°C] for a solenoid valve where C = 2 [dm
3
/(s·bar)] and b = 0.3.
293
According to formula (1), the maximum flow rate = 600 x 2 x (0.4 + 0.1) x ————— = 600 [dm
3
/min (ANR)]
273 + 20
0.3 + 0.1
Pressure ratio
= ————— =
0.8
0.4 + 0.1
Based on the Graph (1), the flow rate ratio is going to be 0.7 if it is read with a pressure ratio of 0.8 and a flow ratio of
b = 0.3.
Hence, flow rate = Max. flow rate x flow rate ratio = 600 x 0.7 = 420 [dm
3
/min (ANR)]
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Flow rate ratio
0
Equipment
C , b
P2
Q
P1
b = 0.1
0.2
0.5
0.6
0.3
0.4
Pressure ratio (
P
2 + 0.1) / (
P
1 + 0.1)
Fig. (1) Test circuit based on ISO 6358, JIS B 8390
(4) Test method
Pipe the text equipment to the text circuit shown in Fig. (1). Keep the upstream pressure at a certain constant level above
0.3MPa. First measure the maximum flow rate in saturation. Then, measure the flow rate, upstream pressure and downstream
pressure each at 80%, 60%, 40% and 20% points of the flow rate. Calculate the sonic conductance C from the maximum flow
rate. Also substitute other data for variables in the formula for subsonic flow and obtain the critical pressure rate b by averaging
the critical pressure rates at those points.
Graph (1) Flow characteristics line
Air supply
Thermometer
Flow control valve
Filter Flow meter
ød
3
≥ 3d
1
≥ 10d
3
10d
1
10d
2
3d
1
3d
2
ød
1
ød
2
3d
3
Pressure gauge or
pressure convertor
Differential pressure gauge or
differential pressure converter
Pressure control
equipment
Pipe for measuring
temperature
Equipment
for test
Pipe for measuring
pressure in the
upstream side
Pipe for measuring
pressure in the
downstream side
Shut off
valve
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1