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3.1 Introduction

3.2 Laminar Airflow

3.3 Pressure Differences Move Air

3.4 Draw-Thru Systems

3.5 Pressurized Systems

3.6 Incorrect Airflow Balance

3.7 Correct Airflow Balance

3.8 What Affects Balance

3.9 The Effects of Changing Balance

3.10 Affecting Balance Through Mechanics

3.11 Adaptations During Spraying

3.12 Conclusion

3.10 Affecting Balance Through Mechanics

The practical way of doing this is to install a variable speed drive system (VFD) on the fan to allow the fan speed to increase as the filters load with overspray. There are different ways to control airflow in draw-thru and pressurized systems.

Draw-thru system

A partial perforated plate is installed in the ductwork after the exhaust fan. This acts as an orifice plate of sorts. The differential pressure across this plate is directly proportional to the airflow within the range we wish to control the speed of the fan. As the differential pressure builds, the pressure sensor and pressure controller increases the speed of the fan using the VFD.

Pressurized system

A sensor and a controller measure the room static pressure relative to the outside pressure and adjust the fan speed by using the VFD. It is not important where the sensor is located since the gradation of pressure is essentially linear. If a pressure of -.03” is held at the center of the booth, holding the pressure to -.05” nearer the exhaust filters can have the same good results.

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