Bronkhorst CORI-FLOW - Manual (Page 23)

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.
4.4.4 Bellows valve
These valves are suited for low pressure or vacuum applications. The user should not disassemble this
model.
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
undercritical
If ∆P is 50-100% of supply pressure, use formula:
T
p
K
n
n
m
v
⋅
⋅ ⋅
Φ
= ρ
ρ
1
257
overcritical
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]
9.17.031 page 23