Chapter hvac engineering Fundamentals: Part 1 Introduction

258
Chapter Eight
Figure 8.41
Electromechanical relays.
different. The contact ‘‘rating’’ will be specified as the
inductive
or
resistive
maximum current at a stated voltage. The inductive rating
relates to opening the contact, which creates a tendency to arc across
the opening if current is too high. This causes contact burning and
premature failure.
Pneumatic systems use several different types of ‘‘relays.’’ The
elec-
tropneumatic
(EP)
relay
is a three-way air valve operated by an elec-
tric solenoid. Its normal function is to provide or bleed off control air
as a fan or pump is started or stopped. The typical arrangement is
Design Procedures: Part 6
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