Bronkhorst Mini CORI-FLOW - Manual (Page 31)

BRONKHORST CORI-TECH B.V.
4.4.3 Pilot operated valve
This control valve is an indirect control valve, consisting of a spring loaded membrane/orifice system which is
positioned by a solenoid operated direct control (pilot valve). The two devices are integrated in one block.
Basically follow the same procedures for dis-assembly as stipulated under “Solenoid valves”
For cleaning purposes it may be required to dis-assemble further, i.e. also remove the membrane assembly.
For pilot operated valves the maximum pressure drop is limited to 20 bard. If the pressure drop during start-up
is higher, it is preferred to install a bypass valve. During start-up this valve should be opened. Also the
minimum pressure drop is limited. For exact figures consult factory or proceed according to the technical data
and/or additional instructions given by the sales office or department.
Note:
When pressure testing a system incorporating a pilot operated control valve, a special procedure must be
followed in order to prevent damage to the valve. In such cases it is necessary to contact the factory prior to do
this.
4.5 K
v
-value calculation
This calculation method can be used to determine the K
v
-value of the main orifice of a control valve.
4.5.1 For gases
Determine desired ∆p across valve.
∆ p must be at least 20% of supply pressure, or in closed loop systems, of total pressure difference in the loop.
If ∆p is 20-50% of supply pressure, use formula:
2
514 p p
T
K n
n
m
v ⋅ ∆
⋅
⋅
Φ
=
ρ
ρ
under critical
If ∆P is 50-100% of supply pressure, use formula:
T
p
K
n
n
m
v
⋅
⋅ ⋅
Φ
= ρ
ρ
1
257
over critical
Units:
Φ
m
= flow [kg/h]
p
1
= supply pressure [bara]
p
2
= downstream pressure [bara]
∆ p = pressure difference (p
1
- p
2
) [bara]
T = temperature [K]
ρ
n
= density [kg/m
n
3 ]
The orifice diameter can be determined by: d= 7.6 K
v
[mm]
9.17.050 page 31