Air Compressor Description and Operation Haldex Compressor

The Haldex® Compressor air compressor is a 2-cylinder single-stage, reciprocating air compressor. The air compressor has a rated displacement of 12.9 cubic feet per minute (cfm), at 1250 RPM. The air compressor consists of 2 major sub-assemblies, the cylinder head and the crankcase.

The cylinder head is an iron casting. The cylinder head houses the following components:

The crankcase houses the following components:

The crankcase provides a flanged mounting surface.

The air compressor is pulley driven by the vehicle engine and operates continuously while the engine runs. The air compressor unloading mechanism and the governor control the actual compression of air. The engine oil lubrication system lubricates the air compressor. The engine cooling system cools the air compressor.

An coolant inlet hose provides coolant from the water pump housing to the air compressor. A coolant outlet hose carries hot coolant from the air compressor back to the engine.

The vehicles engine provides a continuous supply of oil to the air compressor. A hose assembly from the engine block to the air compressor oil inlet supplies oil. An oil passage in the air compressor crankcase allows oil to lubricate the connecting rod crankshaft bearings. The connecting rod wrist pin bushings and the crankshaft ball bearings are spray lubricated. An oil return passage in the mounting flange allows the oil to drain back into the engine crankcase.

As the air compressor pistons move downward, the inlet valve of the cylinder head draws air into the cylinder. This is the intake stroke. As the piston begins to move upward, the inlet valve closes and the air above the piston compresses. This is the compression stroke. When air pressure in the cylinder becomes greater than the air pressure in the reservoirs, the discharge valve raises off the seat allowing air to pass through the discharge port and out of the discharge line. As the intake stroke begins, the discharge valve spring and the air pressure in the discharge line return the discharge valve to the seat. This prevents the compressed air in the discharge line from returning to the cylinder bore as the intake and compression cycles repeat.

The Bendix® AD-IS governor operates in conjunction with the air compressor unloader mechanism. The governor automatically controls the air pressure in the air brake supply system between a maximum cut-out pressure and a minimum cut-in pressure. The air compressor runs continually while the engine runs. The governor actuates the air compressor unloader mechanism, controlling the actual compression of air. The mechanism stops or starts the compression of air when the pressure in the air reservoir reaches maximum or the minimum.

When the air pressure in the system reaches the governor cut-out pressure, the governor allows air to pass from the air reservoir, through the governor and into the cavity above the unloader pistons. The unloader pistons move down holding the inlet valves off of their seats. With the inlet valves held off of their seats by the unloader pistons, air is pumped back and forth between the two cylinders and the discharge valves remain closed. When the air pressure from the reservoir drops to the cut-in setting of the governor, the governor closes and exhausts the air from above the unloader pistons. The unloader springs force the pistons upward and the inlet valves return to their seats, allowing air compression to resume.

Air Compressor Description and Operation Wabco Compressor

The Meritor WABCO System Saver 318 air compressor provides and maintains air under pressure to operate devices in the air brake and auxiliary air systems of a vehicle. It consists of 2 major subassemblies--Cylinder head and crankcase/cylinder block.

The cylinder head contains the inlet, discharge and unloader valving, as well as an integral relief valve. There are 2 water ports, an air discharge port and an inlet port. The cylinder head is mounted on the crankcase/cylinder block.

The crankcase/cylinder block contains:

The compressor is driven by the engine and its crankshaft turns continuously while the engine is running. Compression of air is controlled by the governor and by the compressors unloading mechanism.

The governor maintains the brake system air pressure at preset maximum and minimum levels. The governor is mounted apart from the compressor, either horizontally or vertically. The governor port is located on the crankcase of the compressor.

The unloader mechanism controls the air compression cycle; an air compression cycle has three phases:

1. Induction--Air flows from the engine to the compressor, opening an inlet valve in the cylinder head of the compressor.
2. Compression--Air pressure is increased, causing the compressors discharge valve to open.
3. Unloading--Air passes from the cylinder to the inlet chamber of the cylinder head via a port controlled by a sliding leaf valve.

When system cut-in pressure is reached, air is exhausted from the unloader port.

4. After unloading, the unloader piston returns the sliding leaf valve to the loaded position. This seals the unloader ports and compression resumes.