17
5041A2E4
Install the new Control Unit and tighten the two (2) screws firmly again. If a
shut-off manifold is installed; do not forget to open up the two (2) shutoff val-
ves again, in order to get a proper function of the Flow Monitor.
Connect the electrical cables according to your new Control Unit’s possibili-
ties and for detailed information regarding wiring, please see section 2.7
”Electrical installation”.
Pressure Drop
The Eletta Flow Monitor is a differential pressure measuring device and there-
fore it creates a certain pressure drop when in function. There are two different
types of Pressure Drop’s involved, actual pressure drop and permanent
pressure drop. Below we will explain the difference between these two:
When the orifice plate mounted in the Eletta Flow Monitor reduces the flow
area inside the pipe system, a pressure drop over the orifice is created. This is
what we call actual pressure drop. Please refer to chapter 1.1 ”Description”
for actual pressure drop (differential pressure span).
The calculation of the flow is using this pressure drop to calculate the actual
flow value (see calculation below). The actual pressure drop is a temporary
pressure state and the Eletta Flow Monitors are working within this differenti-
al pressure created within the Flow range of the Monitor. When the flow has
passed the Monitor, the pressure is then trying to get back to its original pres-
sure and normally after 10 - 15 times the inner diameter of the pipe, the flow
becomes linear and fully developed. This is a normalized flow but due to fric-
tion losses over our Flow Monitor, the pressure will not be able to reclaim all
the energy (pressure). This is what we call permanent pressure drop.
The permanent pressure drop can be calculated approximately by ∆ρ
(ppd) =
∆ρ(apd) • (1-β
2
), where the symbols represent:
∆ρ
(ppd) = permanent pressure drop
∆ρ
(apd) = actual pressure drop (see formula below ”actual pressure
drop graph” for calculation)
β = d/D ratio (ratio between bore and inner diameter of the pipe).
This means that for the normal β range (0.2 - 0.7) a typical permanent pres-
sure drop ranges from 0.96 ∆ρ and 0.51 ∆ρ can be expected.
Example:
For the Eletta Flow Monitor S2-GL15 with a flow range of 10 - 20 l/min, the
following example can be used for how to calculate the ∆ρ
(ppd) permanent
pressure drop) at 15 l/min for the said Monitor:
To Next Page
Loading...
