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Master Catalog 125
Pressure Controls Section P
Product Bulletin P74
Issue Date 0204
Specifications
Part No. 997-545, Rev. C
Code No. LIT-125490
P74 Series
Differential Pressure Controls
Application
The controls are available for
applications sensing air, oil or
liquid. Typical applications are
proof of flow across a chiller or
water cooled condenser, proof of
flow in a heating or cooling coil
and lube oil pressure sensing on
refrigeration compressors. On a
proof of flow application the
control measures pressure drop
across two different points in
either a closed water circulating
system or a city water to supply
system.
These differential pressure
controls are for use as operating
controls and/or indicating system
functions through display lights or
panels. They measure the
difference in pressure exerted
upon its two sensing elements.
Fig. 1: P74 Differential Pressure
Control with
Style 13 elements.
On a proof of flow application in a
water chiller system the control
activates a light or signal to
indicate a loss of water.
The control may also be applied
as a lube oil pressure sensing
control on refrigeration
compressors. They may be used
in combination with P28 and/or
P45 oil pressure cutout controls
on two compressor, single motor
units to reduce the oil system
cost. (See Fig. 4.) Special low
pressure models are available for
variable speed and screw
compressor oil pressure
applications.
All Series P74 differential
pressure controls are designed
for use only as operating
controls. Where an operating
control failure would result in
personal injury and/or loss of
property, it is the responsibility
of the installer to add devices
(safety, limit controls) or
systems (alarm, supervisory
systems) that protect against,
or warn of, control failure.
© 2004 Johnson Controls, Inc. 1