Chapter hvac engineering Fundamentals: Part 1 Introduction

8.3.2.2
Modulating controllers.
The methods which controllers use to
determine the value of the output signal have already been discussed.
To be considered here are the various energy types used by HVAC
controllers.
By far the most common, historically, are pneumatic devices. The
principle of the nonbleed relay-type pneumatic controller is shown in
Fig. 8.23. When the sensor causes a downward movement against the
lever, the air supply valve opens and air pressure increases in the
chamber and in the output. The flexible diaphragm pushes upward
Design Procedures: Part 6
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