6
MPA IO&M
B51223-005
P
To Piezo Ring
To Front Panel
B
A
Front Pressure Tap
HIGH PRESSURE
Piezometer
LOW PRESSURE
A
B
Piezometric Data
How It Works
The Piezo system is based on the principle of a flow
nozzle. The inlet funnel of the fan is used as the flow nozzle,
and the flow can be calculated by measuring the static
pressure drop through the inlet funnel. The pressure drop is
measured from the tap located on the face of the inlet funnel
to the piezometer in the throat. The inlet tap is connected to
the high-pressure side of the transducer and the piezometer
is connected to the low-pressure side (see following
diagram).Measurement of Airflow
Several factors affect the accuracy of this method of
determining flow. The equations below assume the following:
• There are no vanes or other obstructions in or near the inlet
• Impeller to inlet funnel overlap
• Flow entering the funnel (no pre-swirl)
• Accurate determination of air density at the inlet
K Factor Table
Model
K Factor
100
592
120
842
135
963
150
1147
165
1450
180
1671
195
2087
225
2458
245
2941
270
4156
300
4810
330
5748
365
7072
402
8609
Calculation when using the Piezometer
For standard air (ρ = 0.075 lb/ft3) :
(CFM) = K Factor * √(delta pressure)
• K Factor = value from chart
•
Delta Pressure (ΔP) = The differential in static pressure
from the piezometer and the front pressure tap (inches
w.g.)
