1. Front (reserve) tank drain valve. 2. Center (dry)
tank drain valve. 3. Rear (wet) tank drain valve.
7. If the pressure on the gauge on the machine is more
than 15 psi (105 kPa) different than the pressure on the
test gauge, install a new gauge.
8. If it is necessary to install a new gauge, stop the
engine and open the front and center drain valves until
the pressure in the tractor reservoirs is released.
9. Do not disconnect the test gauge. It will be used in
Before the test equipment is disconnected,
make sure all pressure is released from the
tractor reservoirs. To prevent personal injury,
make reference to WARNING on first page of
AIR SYSTEM AND BRAKES TESTING AND
Air Compressor Governor
1. Start the engine and let the pressure go up to the
2. Read the cutout pressure on the test gauge.
3. Push the brake pedal rapidly several times.
4. Read the cut-in pressure on the test gauge.
5. The cut-in pressure is 100 to 105 psi (690 to 725
kPa). The cutout pressure is 125 5 psi (860 35
1. Compressor. 2. Governor.
6. If necessary, make an adjustment to the air
compressor governor as follows:
Remove cover (I) on top of the governor.
Loosen the locknut on the adjustment screw.
Turn the adjustment screw counterclockwise to
make the cutout pressure higher. One turn of
the adjustment screw changes the pressure
approximately 20 psi (140 kPa). The cut-in
pressure will change the same amount.
7. If the adjustment screw does not change the cutout
pressure, the unloading valves in the air compressor
are not working correctly.
8. If the cut-in to cutout pressure difference is not
correct, the governor is not working correctly.
Air Relief Valve
The air relief valve opens at 150 psi (1030 kPa) and
has no adjustment.
Parking Brake Control Valve
Start the engine and let the pressure go up to cutout
pressure [125 + 5 psi (860 + 35 kPa)].
2. With the control knob for the parking brake in the OFF
position (pushed in), stop the engine.
3. Hold the control knob for the emergency brakes in the
OFF position (pushed in). Push the brake pedal
automatically moves to the ON position.
4. Read the pressure on the gauge.
5. The correct pressure to automatically engage the
brakes is 40 + 5 psi (280 + 35 kPa). If the pressure on
the gauge is not correct, the operation of the control
valve is not correct.