FLOW OF AIR; RELEASING OF PARKING BRAKE
1. Knob and pin assembly. 2. Valve body. 3. Spring. 4.
Orifice. 5. Outlet (to chamber of the parking brake). 6.
Inlet (from air reservoir). 7. Exhaust (to atmosphere). 8.
The control valve will be ON when there is little air
in the air reservoir [knob (1) pulled out]. Valve (8) is
against the upper face of valve body (2) to stop pressure
air to outlet (5) and exhaust (7). Air in the reservoir
goes up to the necessary range.
When the pressure gauge gives the indication that
the necessary air is in the reservoir, push in and hold
knob (1) to release the parking brake. Pressure air from
the reservoir goes in inlet (6), through orifice (4) and
through outlet (5), into the brake chamber, to release the
parking brake. Air pressure holds valve assembly (8)
over exhaust (7).
If the air pressure in the system goes below 40 ± 5
psi (280 ± 35 kPa), spring (3) moves valve assembly
(8), opening exhaust (7). Pressure air goes to the
atmosphere and the parking brake activates.
During normal operation, air pressure goes into
supply port (7), around valve (6), and out through
delivery port (4).
When the valve is activated, air pressure comes
from the tee at the horn valve into control port (3). This
air pressure pushes piston (1) up and compresses spring
(2). Valve (6) comes in contact with the valve body and
stops the flow of air pressure through delivery port (4).
Any air pressure in delivery port (4) is released through
exhaust passage (5).
1. Piston. 2. Spring. 3. Control port. 4. Delivery port.
5. Exhaust passage. 6. Valve. 7. Supply port.