Fig. 2 Tractor Protection Valve
13 VALVE, Rubber
14 SEAL, O-Ring
15 SEAL, O-Ring
16 SEAL, O-Ring
18 SEAL, O-Ring
21 SEAL, O-Ring
bly (5) away from body seat (20), seats assembly (5)
against rubber valve (13) and pushes it away from spool
seat (7). Service and emergency air passages from
tractor to trailer ports are open.
Exhaust seats are closed, blocking air from passing
through cavities "B" and "C" to atmosphere.
During normal service brake release, brake control air
protection valve acts to unseat valve (13) from exhaust
valve (5). Air enters cavity "C," goes through "B" and out
exhaust port (J).
Air upstream from tractor protection valve is exhausted
through foot valve or hand control valve.
If tractor brake system pressure drops to 172276 kPa
(25-40 psi), spring force (19) moves piston (17) towards
exhaust port (J). Simultaneously, springs (6) and (12)
push assembly (5) and valve (13) to follow. Tractor-to-
trailer passages are closed and trailer emergency air is
If the two-way air control valve is pulled "out" for
emergency braking or uncoupling trailer, the pilot air
exhausts from cavity "A." Tractor protection valve attains
closed position and trailer brakes apply.
Once each year or every 160,000 km (100,000 miles)
remove, disassemble and clean all parts. All rubber
parts must be replaced.
Use air pressure source equipped with in-line manual
shut-off air gauge and connection.
Install pipe plugs in any threaded ports not shown or
labeled by Fig. 2.
Connect air line to tractor service port (E).
Open manual valve slowly to build up 681-861 kPa (100-
125 psi) and shut off manual valve. No air leakage is
permissible through end cover and body casting
surfaces, around screws and jointing flanges. No air
leakage permissible that is passing through valve and
evident at tractor emergency, trailer service (E) and
emergency (D) or exhaust (J) ports.
Disconnect air line from tractor service port and connect
to tractor emergency port. Build up 681-861 kPa (100-
125 psi),pressure. No air leakage permissible through
surrounding casting surfaces. No leakage permissible
through valve and evident at tractor service (F), trailer
service (E), and emergency or exhaust ports. Disconnect
Connect air line to control port. Build up 681861 kPa
(100-125 psi) air pressure. No air leakage permissible
through casting surfaces or evidence of air leakage out
any of the other five open ports or around end cap snap
ring. Disconnect air line.
Performance Checks: An additional manifold fixture with
two connections, air gauge and manual shut-off valve will
be required for performance checks. Preferably, the
manifold should be supplied with air by a separate line to
the air source.
Install separate air gauges in trailer service and
emergency ports (E and D). Connect manifolded fixture
to control port (H) and tractor emergency port (G). Open
manual valve to allow 345379 kPa (50-55 psi) air
pressure build up to both ports. Shut off manual valve.
Pressure build up at trailer emergency port (D) should
have occurred. Gauge at trailer service port (E) must not
show pressure. Permissible leakage at exhaust port is a
25 mm (1") diameter bubble in six (6) seconds.
CTS-4079 - CHAPTER XI - Page 4