TECHNICAL DESCRIPTION
MULTICAL® 62
Ka st up A/“ •
Technical
Des iptio •
5512-1036-GB_D1
•
.2016
52
9.5
Flow limits
I the ete s o ki g a ge f o i . ut
-off and far beyond Q
4
there is a linear connection between the
flow rate and the measured water flow.
In practice, the highest possible water flow through the sensor will be limited by the pressure in the system
or cavitation due to too low back pressure.
If the flow is lower than min. cut-off
–
or negative
–
ULTRAFLOW® 24 does not measure any flow.
According to OIML R49, the upper flow limit Q
4
is the highest flow, at which the flow sensor may operate
for short periods of time, without exceeding maximum permissible error. ULTRAFLOW® 24 has no
functional limitations while operating above Q
4
. Please note, however, that high flow velocities > Q
4
involve
the risk of cavitation, especially at low static pressures.
9.6
Guidelines for dimensioning ULTRAFLOW® 24
In installations, it has shown appropriate to work with pressures higher than the pressures shown below:
Nominal flow Q
3
Recommended minimum
operating pressure
Max. flow Q
4
Recommended
operating pressure
[m³/h]
[bar]
[m³/h]
[bar]
1.6
1.5
2
2.5
2.5
1
3.1
2
4
1
5
2
6.3
1.5
7.9
2.5
10
1
12.5
2
16
1.5
20
2.5
25
1
31
2
40
1.5
50
2.5
Table 9
The purpose of recommended minimum operating pressure is to avoid measuring errors as a result of
cavitation or air in the water.
It is not necessarily cavitation in the flow sensor part itself, but also bubbles from cavitating pumps or
regulating valves, mounted before the sensor.
In addition, the water may contain air in the form of small bubbles or air in the water.
The risk of influence from these factors is reduced by maintaining a fair pressure in the installation.
Furthermore, it must be taken into consideration that the above-mentioned pressure is the pressure at the
sensor and that the pressure is lower after a contraction than before (e.g. cones). This means that
pressure, measured elsewhere in the system, may be different from the pressure at the sensor.
This a e e plai ed o
i i g the o ti uit e uatio a d Be oulli s e u
ation. The total energy from
the flow will be the same at any cross section. It can be reduced to:
P + ½
v
= constant, where P
is the
pressure,
is the density of water and v is the flow velocity.
Dimensioning the flow sensor, the above must be taken into consideration, especially if the sensor is used
within the scope of OIML R49 between Q
3
and Q
4
, and in case of strong contractions of the pipe.
