Pitot Tube and Gauge
Figure A
Placement of the Pitot Tube
Pitot Tube
Note: For best results keep Pitot tube
well away from dampers.
Figure B
This is an example for determining the airflow in a 6" duct. The Pitot tube reading was 0.025 inches of water. From the chart, this is 640 feet per minute.
The 6" duct has a cross sectional area of:
=[3.14 x (6"÷12)2]÷4
=0.2 square feet
The airflow is then:
640 ft./min. x 0.2 square feet = 128 cfm
For your convenience, the cross sectional area of some common round duct is listed below:
DUCT DIAM. (inches) CROSS SECTION AREA (sq. ft.)
5.0 | .14 | |
6.0 | .20 | |
7.0 | .27 | |
| INSULATED PIPE | |
| WITH VAPOUR | |
BARRIER | ||
| ||
BALANCING | OUTSIDE | |
DAMPERS | ||
HOOD | ||
| ||
| BACK DRAFT | |
| DAMPER | |
| Figure C |
The accuracy of the airflow reading will be affected by how close to any elbows or bends the readings are taken. Accuracy can be increased by
taking an average of multiple readings as outlined in the literature supplied with the Pitot tube.
Balancing Collar Instructions
Push and turn with slotted screwdriver. Damper automatically locks when pressure is released.
Insulated flexible
ducting
When connecting ductwork to the collar, take note where screws are located. Screws should be located no further than 1/2” from outside edge of collar, so as not to impede operation of the damper.
1/2”
Figure D
26
