Air System; Air System Inspection; Air System Functional - Midland SIDE DUMP GRAVEL TRAILER Operator's Manual

5.2.13

AIR SYSTEM

Trailers are equipped with an air system, that is
pressurized by a compressor on the tractor, for
operating the "discharge gates", brakes and air
suspension (if so equipped). All components must
be in good condition for the system to function
and perform as intended. The air system must be
inspected to be kept in good condition and functional
checks performed to be sure it is operating as
required.
5.2.13.1

AIR SYSTEM INSPECTION

The pre-trip or pre-start inspection include several air
system related checks, inspections or tasks including
but not limited to:
Daily
1. Check that the glad hands are clean and in good
condition. Check seals in glad hand Clean, repair
or replace as required.
2. Check that the air hoses between the tractor and
the trailer are routed to prevent rubbing, chaffing
or pinching. Reroute to correct condition if
required.
3. Drain moisture from all air tanks. Pull on the
cable attached to drain valve on the bottom of
each tank until the water or spray no longer can
be seen.
IMPORTANT
Tanks must be drained daily in high
humidity and cold temperature conditions to
prevent getting water or ice in the system.
During cold weather operation use only
recommended air line anti freeze in the
trailer air system. Alcohol or methyl hydrate
is not to be used because they will remove
vital lubricants causing premature failures
of valves and components. Traces of these
products will void any warranty consideration.
4. Check that all the lines and hoses conveying
air along the frame are tied up and secured to
prevent dragging, scuffing or snagging. Tie up
or protect as required to correct the condition.
Damaging an air system component can cause
a sudden loss of pressure and result in a loss of
service brakes.
IMPORTANT
New FMVSS-121 regulations mandate
higher pressures in the supply line to insure
proper brake operation. Set the compressor
pressure for cut-in to 105 psi and cut-out
to 120 psi. Do not use additives in the air
systems.system.
5.2.13.2

AIR SYSTEM FUNCTIONAL

A vehicle air system is a combination of the
components on the tractor and the trailer. All must
be maintained in good condition for the entire system
to function as required. Although a visual check will
indicate the outer condition of the components, it
does not indicate the leaks or responsiveness of the
system. To evaluate the integrity and responsiveness
of the system, perform these functional checks:
1. Attach the trailer to a tractor and connect all the
air and electrical lines.
2. Block wheels.
3. Stop tractor engine and exhaust air from all tanks.
4. Start engine and run at fast idle (1200-1500 RPM)
to charge the air system.
Verify that:
a. Low pressure alarm goes off when the
system pressure drops below 50 psi.
b. Increasing the system pressure between 50
psi and 80 psi takes less than 3 minutes.
c. The compressor cuts out when the system
pressure drops below 120 psi.
d. Fan brakes to use air. Compressor must
engage when system pressure drops below
105 psi.
Release spring brakes before fanning service
brakes.
5. Push emergency valve to charge trailer system.
Apply and release service brakes.
6. Build system up to 120 psi and stop engine.
Verify that:
a. Main tank pressure does not drop more than
18 psi when brakes are fully applied using
brake pedal. If pressure drop exceeds 18 psi,
adjust brakes and recheck.
b. System pressure should not drop more than 4
psi per minute. Listen for audible leaks.
c. Release foot valve to drop main reservoir
pressure. Brakes should dynamite
automatically when the pressure drops below
60 psi.
Adjust or repair system until these conditions are
met.
NOTE
77