MCi Crusader II 1989 Maintenance Manual page 386

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MC-9 MAINTENANCE MANUAL
LOADING OPERATION
When loaded. the body of the coach settles. Since the height
control valve is linked to the suspension, and the valve is
mounted to the vehicle body, the valve moves downward with
the body during loading. As the overtravel lever and control
shaft turns, the intake valve lever presses against the pin of the
valve core. As the pin is depressed, air pressure flows through
the height control valve into the air springs. Increased the air
pressure expands
the
air springs and raises the body of vehicle.
The intake valve is protected by a check valve which permits air
to travel in one direction only.
NEUTRAL POSITION
Increased pressure expands the air springs lifting the vehi-
cle body and height control valve. The overtravel lever returns
to "neutral" as vehicle body approaches normal ride height.
The intake valve lever also moves the closing valve. The
exhaust valve r_emains closed and the check valve in intake
adapter prevents air from escaping from the valve body and air
springs. This condition remains static until coach load is
altered, moving the overtravel lever from ·•neutral" for one or
more secC'nds actuating the intake or exhaust valves.
UNLOADING OPERA1ION
When the load is lightened, pressure in the air springs raises
· the coach body. Overtravel lever is pulled downward from
"neutral." This applies a force that slowly moves the delay
piston and opens the exhaust valve when the lever moves
beyond free travel range. The intake valve remains closed
allowing air from the air springs .to exhaust to atmosphere. As
air is exhausted from air springs. the vehicle body is lowered
until the overtravel lever returns to neutral position.
When the coach is in motion with body at normal ride height,
the overtravel lever is in neutral position. Small movements of
the lever may occur without activating the control valve as it
must move in excess of 3/ 16" (4. 7 mm) before either the inlet or
exhaust valve is opened.
The delay piston, connecting through a pin to overtravel
shaft is contained in a cylinder of silicone fluid. The slowing
action of this fluid delays by 1 to 6 seconds the closing of one
valve to the opening of the other. The flapper valves allow both
valves
to
close ·from full-open position within 1 second.
The overtravet piston is held against the shaft by two springs
(one inside the other) and keeps the shaft in proper position
relative to the overtravel lever. The purpose of the piston is to
prevent damage of parts inside the control valve if the lever
exceeds normal travel, and to allow the lever to move without
moving parts inside the valve.
REMOVAL
1. Support coach by placing blocks under body at jacking
points.
2. Open drain cock in air filter and vent all air from system.
3. Disconnect overtravel lever from link and pull down to
exhaust remaining air from air beams.
4. Disconnect both lines from control valve and cover the
ends with tape to prevent contamination.
5. Detach height control valve from mounting bracket.
Replacement is the reverse of removal. After assembly,
check for leakage using soap and water solution.
LEAKAGE TEST
The following procedure is a leakage test when the valve
assembly is removed from vehicle.
1. Clean the exterior of the valve assembly.
2. Connect air pressure line to air valve inlet port, then open
the air pressure (70• 100 psi;
483·690
kPa).
3. Dip the valve assembly in a container of water and watch
for air bubbles when the overtravel lever is in the center posi•
tion. No air should escape from any point of the valve assembly.
4. If bubbles appear from the bellows port, this is an indica•
tion that the air inlet valve assembly is defective and must be
replaced.
5. Remove the air pressure line from the air inlet port and
connect it to the bellows port. If bubbles appear at the air inlet
check valve port, this is an indication that check valve unit is
defective and must be replaced.
6. If bubbles appear at the exhaust port, it is an indication
that the exhaust ~alve assembly is defective and must be
replaced.
7. If bubbles appear around edge of the valve cover plate,
the cover plate gasket should be replaced.
·8. If no leaks are found, remove the valve assembly from the
water. then with air pressure still connected to the bellows port,
actuate the overtravel lever to remove any excessive amount of
water which may have entered the exhaust valve chamber.
Remove the air line and connect it to the air inlet port to remove
water from the air inlet valve chamber.