GILLIG LOW FLOOR, Service Manual, Page: 209 / 506

209
Air System
Low Air Pressure Switches
The low air pressure switches (Figure 6-18), mounted
under the driver’s platform, are safety devices that
automatically give a warning when pressure in the air
system falls below a safe limit for brake operation.
There are two switches, one for the primary air (rear
brakes) and one for the secondary air (front brakes).
The low air pressure switch is air actuated and operates
an electrical circuit, controlling an indicator light and
warning buzzer.
When air system pressure is above 90 psi, the switch
contacts open to break the circuit to the indicator light
and buzzer. When air pressure drops below 70 - 66 psi
(483-455 kPa) the switch contacts close to energize the circuit to the indicator light and buzzer. Opera -
tion of the low air pressure switch may be checked by reducing system pressure and being sure that the
contacts close when reservoir pressure is between 70 and 66 psi (483-455 kPa). The contacts will be
closed when the indicator light and buzzer operate. (The 66 psi switch has a ± 4 psi variance).
Safety Valve
The safety valve (Figure 6-17) is installed in the wet tank to prevent pressure
buildup in the tank beyond the set maximum. When the supply air pressure
builds up to a maximum of 150 psi the valve ball is forced off its seat and the
excess pressure is exhausted to the atmosphere. When the pressure is reduced
to below the set maximum the valve spring forces the ball back onto its seat
and pressure accumulation in the tank may continue.
Check the safety valve periodically for leaks by applying a soap solution to the
exhaust port. Leakage should not exceed a one inch bubble in five seconds.
The release pin should be moved to ensure the valve is free to function as
described.
Figure 6-17, Safety Valve
VALVES AND PRESSURE SWITCHES
Figure 6-18, Air Pressure Switch