MULTICAL® 302
Kamstrup A/S · Technical Description · 5512-1334_F1_GB_12.2016
31
6.5
Operating pressure of MULTICAL
®
302
In connection with installations it has proved practical to work with minimum the pressure mentioned below:
Nominal flow q
p
Recommended back
pressure
Max. flow q
s
Recommended back
pressure
[m³/h]
[bar]
[m³/h]
[bar]
0.6
1
1.2
2
1.5
1
3
2
2.5
1
5
2
Table 3
The purpose of recommended back pressure is to avoid measuring errors as a result of cavitation or air in the water.
It is not necessarily cavitation in the sensor itself, but also bubbles from cavitating pumps and regulating valves
mounted before the sensor. It can take some time until such bubbles have been dissolved in the water.
Furthermore, water can include dissolved air. The amount of air which can be dissolved in water depends on pressure
and temperature. This means that air bubbles can be formed due to falling pressure, e.g. caused by a velocity rise in a
contraction above the sensor.
The risk of these factors affecting accuracy is reduced by maintaining a fair pressure in the system.
In relation to above table, the steam pressure at the current temperature must also be taken into consideration. Table
3 applies to temperatures up to approx. 80 °C. Furthermore, it must be taken into account that the above-mentioned
pressure is the back pressure at the sensor, and that the pressure is lower in a contraction than before one (cones
among other things). This means that pressure measured elsewhere in the system may be different from the pressure
at the sensor.
This can be explained by combining the continuity equation and Bernoulli’s equation. The total energy from the flow
will be the same at any cross section. It can be reduced to: P + ½
ρ
v
2
= constant.
When dimensioning a flow sensor you must take this into account, especially if the sensor is used within the scope of
EN 1434 between q
p
and q
s
, and in case of heavy contractions of the pipe.
Diagram 3
0
0,5
1
1,5
2
2,5
3
80
85
90
95
100
105
110
115
120
125
130
[b
ar
]
[°C]
Steam pressure