3
SeCTIoN 1 - INTRoDUCTIoN
1-1. General
The Barton
®
weatherproof Model 289A and the explosion-proof Model 291B are
differential pressure indicating switches (Figure 1-1). The 289A has a NEMA-4
watertight die-cast aluminum case (finished with a weather-resistant black epoxy
resin paint). The cover lens is secured in the bezel with an elastomer ring to
reduce the possibility of accidental breakage. This ring also acts as a seal between
the bezel and the case to ensure a moisture, fume and dust-free atmosphere for
the indicator and switch mechanism.
Model 291B has an explosion-proof case that is certified for Class I, Division 1,
Groups B, C & D service. The large cover lens allows maximum readability of the
indicating pointer.
Switches and all adjustments are readily accessible when the cover is removed
(Figure 1-2, page 4). The built-in switches energize either single or dual alarm
circuits when the measured differential pressures exceed predetermined limits.
These limits may be either maximum, minimum, or both.
figure 1-1. Model 289a (left) and Model 291b (right) Differential Pressure
Indicating Switches
