Datasheet

2.3 Flow coefficient Cv factor
The United States Standard ANSI/(NFPA)T3.21.3: 1990: Pneumatic fluid power—Flow rating test proce-
dure and reporting method for fixed orifice components
Defines the Cv factor of flow coefficient by the following formula which is based on the test conducted by the
test circuit analogous to ISO 6358.
Q
Cv
= ——————————— ·········································································(7)
ΔP (P2 + Pa)
114.5
——————
T1
ΔP : 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 – ΔP
Q
: Flow rate [dm
3
/s standard condition]
Pa : Atmospheric pressure [bar absolute]
T1 : Upstream absolute temperature [K]
Test conditions are < P1 + Pa = 6.5 ±0.2 bar absolute, T1 = 297 ±5 K, 0.07 bar ≤ ΔP ≤ 0.14 bar.
This is the same concept as effective area A which ISO 6358 stipulates as being applicable only when the
pressure drop is smaller than the upstream pressure and the compression of air does not become a problem.
3. Process fluid control equipment
(1) Conformed standard
IEC60534-2-3: 1997: Industrial process control valves. Part 2: Flow capacity, Section Three-Test proce-
dures
JIS B 2005: 1995: Test method for the flow coefficient of a valve
Equipment standards: JIS B 8471: Solenoid valve for water
JIS B 8472: Solenoid valve for steam
JIS B 8473: Solenoid valve for fuel oil
(2) Definition of flow-rate characteristics
Av factor: Value of the clean water flow rate represented by 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.
Av = Q ———— ····························································································(8)
ΔP
Av
: Flow coefficient [m
2
]
Q : Flow rate [m
3
/s]
ΔP : Pressure difference [Pa]
: Fluid density [kg/m
3
]
(3) Formula of flow rate
It is described by the practical units. Also, the flow-rate characteristics are shown in Graph (2).
In the case of liquid:
ΔP
Q
= 1.9 x 10
6
Av ———— ···············································································(9)
G
Q
: Flow rate [L/min]
Av : Flow coefficient [m
2
]
ΔP : Pressure difference [MPa]
G : Relative density [water = 1]
In the case of saturated aqueous vapor:
Q = 8.3 x 10
6
Av ΔP(P2 + 0.1) ·······································································(10)
Q : Flow rate [kg/h]
Av : Flow coefficient [m
2
]
ΔP : Pressure difference [MPa]
P1 : Upstream pressure [MPa]: ΔP = P1 – P2
P2 : Downstream pressure [MPa]
ρ
ρ
Series VXZ
32