or 1.18 psi. The switch resets when the pressure drops to
25 inches of water or 0.93 psi.
When the switch actuates
on a pressure increase, it turns on the FILTER CLOGGED
light on the commander's control panel.
When the switch resets on a pressure drop, the light goes
out.
The switch uses a dual diaphragm system to prevent
contamination if a single diaphragm fails.
The area
between the diaphragms vents to the outside.
Figure 1-41. NBC Filter Differential Pressure Switch and Tubing.
If the switch fails due to high-pressure
diaphragm rupture, it will not turn on the warning light if
the filters become clogged; if the diaphragm on the low-
pressure side fails, the switch may turn on the light
prematurely.
When the contacts in the switch stick on
contact "A," the light stays on, and if the contacts in the
switch stick on contact "C," the light will not light.
When a leak occurs in the high-pressure line, it prevents
the switch from actuating at the right pressure, and if a
leak occurs in the low-pressure line, the switch may
actuate prematurely.
36
OD1705
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