Datasheet
Front matter 4
Solenoid Valves Flow Characteristics
2.3 Flow coefficient
Cv
factor
The United States Standard ANSI/(NFPA)T3.21.3:1990: Pneumatic fluid power—Flow rating test procedure
and reporting method for fixed orifice components
defines the flow coefficient Cv factor by the following formula which is based on testing conducted with a test circuit analogo us to
ISO 6358.
Q
Cv
= ——————————— ·········································································(7)
∆
P
(
P2
+
Pa
)
114.5 ——————
T1
∆
P
: Pressure drop between the static pressure tapping ports [bar]
P1
: Pressure of the upstream tapping port [bar gauge]
P2
: Pressure of the downstream tapping port [bar gauge]:
P2
=
P1
–
∆
P
Q
: Flow rate [dm
3
/s standard condition]
Pa
: Atmospheric pressure [bar absolute]
T1
: Upstream absolute temperature [K]
Test conditions are <
P1 + P
a
=
6.5 ±
0.2 bar absolute,
T1
= 297 ± 5K, 0.07 bar ≤
∆
P
≤ 0.14 bar.
This is the same concept as effective area
A
which ISO6358 stipulates as being applicable only when the pressure drop is small
in relation to the upstream pressure so that the compression of air is negligible.
3. Equipment for process fluids
(1) Standards conforming to
IEC60534-2-3: 1997: Industrial process control valves. Part 2: Flow capacity, Section Three-Test
procedures
JIS B 2005: 1995: Test method for the flow coefficient of a valve
Equipment standards: JIS B 8471: Regulator for water
JIS B 8472: Solenoid valve for steam
JIS B 8473: Solenoid valve for fuel oil
(2) Definition of flow characteristics
Av
factor: It is the value representing the flow of clean water in m
3
/s which runs through a valve (equipment for test) when the
pressure difference is 1 Pa. It is calculated using the following formula.
ρ
Av
=
Q
————·····································································································(8)
∆
P
Av
: Flow coefficient [m
2
]
Q
: Flow rate [m
3
/s]
∆
P
: Pressure difference [Pa]
ρ
: Density of fluid [kg/m
3
]
(3) Formula of flow rate
It is described by the known unit. Also, the flow characteristics line shown in the Graph (2).
In the case of liquid:
∆
P
Q
= 1.9 x 10
6
Av
————·······················································································(9)
G
Q
: Flow rate [l/min]
Av
: Flow coefficient [m
2
]
∆
P
: Pressure difference [MPa]
G
: Relative density [water = 1]
In the case of saturated aqueous vapour:
Q
= 8.3 x 10
6
Av
∆
P(P
2
+ 0.1)
··············································································(10)
Q
: Flow rate [kg/h]
Av
: Flow coefficient [m
2
]
∆
P
: Pressure difference [MPa]
P1
: Upstream pressure [MPa]:
∆
P
=
P1
–
P2
P
2
: Downstream pressure [MPa]