27
Air System
and delivery ports, the primary piston (11) will mechanically move the relay piston (24) , allowing the
piston to close the secondary exhaust valve and open the secondary inlet valve and allow air to flow out
the secondary delivery port.
Balanced: No. 1 or Primary Circuit
When the primary delivery pressure acting on the primary piston (11) equals the mechanical force of the
brake pedal application, the primary piston (11) will move and the primary inlet valve (29) will close,
stopping further flow of air from the primary supply line through the valve. The exhaust valve remains
closed preventing any escape of air through the exhaust port.
Balanced: No. 2 or Secondary Circuit
When the air pressure on the delivery side of the relay piston (24) approaches that being delivered on the
primary side of the relay piston, the relay piston moves closing the secondary inlet valve and stopping
further flow of air from the supply line through the valve. The exhaust remains closed as the secondary
delivery pressure balances the primary delivery pressure.
When applications in the graduating range are made, a balanced position in the primary circuit is
reached as the air pressure on the delivery side of the primary piston (11) equals the effort exerted by the
driver’s foot on the treadle. A balanced position in the secondary portion is reached when air pressure on
the secondary side of the relay piston (24) closely approaches the air pressure on the primary side of the
relay piston.
When the brake treadle is fully depressed, both the primary and secondary inlet valves remain open and
full reservoir pressure is delivered to the actuators.
Releasing: No. 1 or Primary Circuit
With the brake treadle released, mechanical force is removed from the spring seat (5), graduating spring
(6), and primary piston (11). Air pressure and spring load moves the primary piston, opening the primary
exhaust valve, allowing air pressure in the primary delivery line to exhaust out the exhaust port.
Releasing: No. 2 or Secondary Circuit
With the brake treadle released, air is exhausted from the primary circuit side of the relay piston (24).
Air pressure and spring load move the relay piston, opening the secondary exhaust valve, allowing air
pressure in the secondary delivery line to exhaust out the exhaust port.
Summary of Contents for LOW FLOOR
Page 18: ...Specifications 18...
Page 58: ...Preventive Maintenance 58...
Page 110: ...Engine 110...
Page 138: ...Transmission Driveline Rear Axle 138...
Page 182: ...Suspension 182...
Page 260: ...Air System 260...
Page 420: ...Electrical System 420 Deutsch DT Series Connectors...
Page 421: ...Electrical System 421...
Page 422: ...Electrical System 422 Deutsch HD 10 Series Connectors...
Page 423: ...Electrical System 423...
Page 424: ...Electrical System 424 Deutsch HD 30 Series Connectors...
Page 425: ...Electrical System 425...
Page 442: ...Heating Air Conditioning 442...
Page 492: ...Body and Interior 492 Figure 11 33 USSC Seat Assembly...
Page 493: ...Body and Interior 493 Figure 11 34 USSC Seat Suspension Assembly...
Page 495: ...Body and Interior 495 Figure 11 37 Seat Air Connections...