SERVICE MANUAL
Fig. 1 Inversion Valve, Type SR-1
1Delivery Port
2Supply Port
3Control Port
4Reservoir Port
BENDIX SR-1 TYPE
DESCRIPTION
The inversion valve is used only on a straight truck
with dual air brake system. Its purpose is to allow a
modulated spring brake application if air loss should
occur in the primary (rear) portion of the air system.
The secondary (front) brakes cannot supply enough
braking effort alone to stop the vehicle quickly to meet
the FMVSS 121 requirements for emergency stopping.
The inversion valve senses the loss of air in the
primary system, allowing the spring brakes on the rear
axle to be applied or released in a modulated manner at
the same time the front service brakes are applied or
released by the operator. The inversion valve also
permits air pressure to enter the parking brake chamber
releasing the spring brakes.
The inversion valve is not required on tractor
applications due to the fact the trailer brakes, being
supplied with air from both the primary and secondary
tractor systems, provide necessary braking required to
meet FMVSS 121 emergency stopping requirements.
1Piston Spring
2Cover
3Large O-Ring
4Piston
5Small O-Ring
6Body
7Check Valve
8Check Valve Spring Guide
9Check Valve Spring
10Pipe Plug
11Exhaust Cover
12Diaphragm
13 Inlet & Exhaust Valve
14Cap Nut
15O-Ring
16Valve Stop
17Valve Spring
18Valve
19O-Rings
20Piston
21Piston Spring
OPERATION
Initial Air Charge (Fig. 3)
Initial air charge from the primary and secondary
reservoirs flows through the spring brake control valve
and enters the supply port of the inversion valve. Air
entering the support port flows past inlet and exhaust
valve "B" to the underside of piston "B" and out delivery
port to the emergency air connection on the spring brake
chamber. Note that the springs above piston "B" force it
into contact with inlet and exhaust valve "B." In the
position shown the exhaust is closed and the inlet is
open.
Only air flowing from the primary reservoir enters the
reservoir port on the inversion valve. This air remains
under piston "A" as system pressure builds up. With
primary reservoir pressure approximately below 379 kPa
(55 psi)
CTS-4079 - CHAPTER VII - Page 3
