The Bendix® Tu-Flo air compressor is a two cylinder single-stage, reciprocating air compressor. It has a rated displacement of 375 L (13.2 cubic feet per minute) at 1250 RPM. It consists of two major subassemblies; the cylinder head and the crankcase. The cylinder head is an iron casting which houses the inlet, the discharge and the unloader valving. The cylinder head also contains the air inlet port, the water inlet and the water outlet ports. The governor is mounted to the side of the cylinder head. The crankcase houses the cylinder bores, the pistons, the crankshaft and the main bearings and also provides a flanged mounting surface (diesel engine).

The air compressor is gear driven (diesel engine) or belt driven (gasoline engine) by the vehicle's engine and is operating continuously while the vehicle's engine is running. The actual compression of air is controlled by the air compressor unloading mechanism and the governor. The air compressor is flange mounted to the diesel engine and bracket mounted to the gasoline engine. The air compressor is lubricated from the engine oil lubrication system and cooled through the engine cooling system. The model identification number is located on an identification plate attached to the air compressor crankcase.

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

The vehicle's engine provides a continuous supply of oil to the air compressor. Oil is supplied through the air compressor oil inlet hose from the engine block to the air compressor oil inlet port. 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. For the diesel engine an oil return passage in the mounting flange allows the oil to drain back into the engine crankcase and on the gasoline engine an air compressor oil outlet hose connected to the air compressor brackets permits the oil to drain back into the engine crankcase.

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

The Bendix® D-2 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 the minimum cut-in pressure. The air compressor runs continually while the vehicle engine runs. The actual compression of air is controlled by the governor actuating the air compressor unloader mechanism which stops or starts the compression of air when the maximum or minimum air reservoir pressures are reached.

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 air 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. This allows the compression of the air to be resumed.

Gasoline engines use an air compressor belt to drive the air compressor. The air compressor belt connects the air compressor pulley to the engine crankshaft pulley.

Gasoline engines use an air compressor air strainer filter to protect the air compressor from dirt in the air. This paper type filter element is located in a housing on the side of the air compressor.