The body is sealed with an endless profile seal ring which in the
standard version is fixed by a retaining ring (DN 150 … DN 1200)
or by retaining segments (all valves of DN > 1400). In closed po-
sition, the elastic profile sealing ring is pressed to the conical seat
surface inside the body and safely seals in both flow directions.
Due to the double offset bearing of the disk, the profile seal ring
is completely unstressed when the valve is in open position. If
required, the profile seal ring can be disassembled without having
to dismantle the valve.
In case of epoxy-coated VAG EKN
®
Butterfly Valves, the sealing
seat is made corrosion-resistant by nickel surfacing and is also
resistant to mechanical damage. In the steel-welded type of the
body, the sealing seat is made of stainless steel. Enamel-coated
bodies are manufactured with an enamel-coated seat. In case of
rubber-lined butterfly valves, the sealing seat is also rubber coa-
ted.
3.2 Applications
In its standard version, the VAG EKN
®
Butterfly Valve is equipped
with EPDM seals.
The VAG EKN
®
Butterfly Valve should only be used in media in
which there is no risk of clogging.
The butterfly valve can be used for the following media:
• Water,
• Raw and cooling water (with appropriate corrosion protection)
• Weak acids and alkaline solutions (with according corrosion
protection)
The use of the valve with media containing gas or oil may result in
the destruction of the EPDM seals (rubber lining) and O-rings and
is therefore not permissible.
For use with gaseous media, NBR seals should be
used.
For information about the temperature limits, please re-
fer to the product-related technical documentation (KAT 1310-A).
In case of differing operating conditions, the manufacturer needs
to be consulted. If in doubt, consult the manufacturer to inquire
about the appropriate sealing materials for your application.
3.3 Performance limits
3.3.1 Cavitation
VAG EKN
®
Butterfly Valves are mainly used to shut off flow. If a
VAG EKN
®
Butterfly Valve is used to control flow, the operational
limits of the maximum flow velocity as well as the cavitation limits
must be observed.
The operational limits can be calculated either using
the VAG UseCAD
®
Planning Software or the following
calculation rules:
Cavitation limits
After the upstream and downstream pressures of the valve as well
as the flow rate have been determined, the cavitation value is cal-
culated as follows:
Calculation of the
σ
-Value:
H1
= Inlet
pressure
[mWC]
H2
= Outlet
pressure
[mWC]
HAt
=
Atmospheric pressure
[mWC]
Hd
=
Evaporation pressure
[mWC]
v
=
Flow velocity in the pipe
[m/s]
g
=
Gravitational acceleration
[m/s²]
The VAG EKN
®
Butterfly Valve has the correct dimensions when
the computed
σ
-value lies above the limit curve of
σ
k. The recom-
mended control range lies between 10-100% opening degree.
Below that no reasonable control can be guaranteed. If cracking
noises or vibrations occur while the valve is being put into opera-
tion, the actual operation conditions should be checked. In case
of changed operation conditions, the equipment may have to be
recalculated. If the computed
σ
-value lies below the limit curves
of
σ
k cavitation will occur.
To remedy the problems, we recommend:
• Changing the back pressure
• Choosing a different place of installation
If the
σ
-value lies above the limit curves of
σ
k the noise is caused
by other criteria and the pipeline will have to be checked.
3.3.2 Maximum permissible flow velocity
While the medium flows through or against the valve disk, the disk
is exposed to forces of flow whose impact is determined by the
flow velocity of the medium in the pipeline. Similar to a wing pro-
file, a greater lift (or buoyancy) is generated at higher flow velocity
and a changed angle of incidence. The same is true for the disk
inside the valve. The buoyancy generated is perceived as torque
at the drive shaft.
According to EN 593 Table 3, VAG EKN
®
Butterfly Valves are de-
signed/sized for the following velocities in liquid media:
• Pressure rating PN 6:
2.5 m/s
• Pressure rating PN 10: 3 m/s
• Pressure rating PN 16: 4 m/s
• Pressure rating PN 25: 5 m/s
• Pressure rating PN 40: 6m/s
In the limit curve chart shown on the following page, you can de-
termine the correct valve pressure rating based upon line pressure
(mWC) and velocity (m/s) see the maximum differential pressure
and the maximum permissible flow velocity for which the desig-
ned dimension of the disk axis and the gears still suffice in the
respective pressure ratings.
VAG Operation and Maintenance Instructions • 5
