AIR COMPRESSOR - MIDLAND BRAKE MODELS EL-1300, EL-1600
All valves and unloader components are installed within
the cylinder head. The inlet and exhaust valve discs are
spring-loaded against seats installed In the bottom of the
head. The unloader mechanism is installed from the top
of the head.
The compressor governor is mounted directly to the
cylinder head or can be remotely mounted. The gover-
nor controls the minimum and maximum air pressure
supplied by the compressor.
With the down stroke of each piston, air Is drawn Into the
cylinder through a disc-type Inlet valve in the cylinder
head. As the pistons begin the upward stroke, the inlet
valve closes and the trapped air above the piston is then
compressed. When the air pressure in the cylinder
becomes greater than the air pressure in the cylinder
head above the exhaust valve, the exhaust valve is then
forced open off its seat. Air is then allowed to pass
through the exhaust port into the head cavity, and from
there into the line leading to the air reservoir. When the
piston starts its downward stroke, the exhaust valve
returns to its valve seat and the compressed air will not
return to the cylinder. The intake and compression cycle
Is then repeated.
UNLOADING (NOT COMPRESSING)
When air pressure in the system reaches the maximum
governor pressure setting, the governor is actuated
causing the unloader pins to hold the inlet valves off their
seats (open). With the inlet valves open, air passes
freely back and forth between the cylinder bores and the
intake cavity in the cylinder head. This suspends the
compression of air until the pressure in the system Is
reduced to the governor cut-in setting. The governor
then exhausts the air pressure to
mechanism, releasing the unloader pins. This allows the
inlet valves to function normally and the resumption of air
Air filters should be cleaned or replaced when the vac-
uum level exceeds 508.0mm (20 Inches) of water at
compression. The governor settings and unloader oper-
ation should be checked regularly. Maximum desirable
reservoir pressure is 826 + 27.6 kPa (125 + 5 psi). Type
of air cleaner, operating conditions and experience may
dictate additional service activity.
Check compressor mounting to be sure it is tight. Be
sure the drive pulleys are in proper alignment and belt
tension is properly adjusted. Make sure the oil supply
and coolant lines are in good condition and not
If the air compressor should fail to maintain sufficient
pressure or supply excessive air pressure, the unloader
mechanism pins or seals could be defective.
The unloader components can be serviced or replaced
without removing the compressor from the vehicles
Refer to disassembly procedures for unloader on page 6
and assembly procedures for unloader on page 11.
Compressor fails to maintain
Dirty intake cleaner
Clean or replace element as
sufficient pressure or adequate
Restriction in compressor
Repair or replace as necessary.
cylinder head intake, discharge
cavities or line.
Leaking or broken inlet or
Repair or replace valves as
Repair or replace compressor as
Drive belt slipping
Adjust or replace belt.
Excessive system leakage
Check all fittings and connections.
Repair or replace governor as
Governor with improper setting
Adjust governor as necessary.
Replace gauge as necessary.
CTS-4077Y - Page 4