Ingersoll-Rand HP600CMH, Operating, Maintenance & Parts Manual

Book 43212455 (11/03)   

15

SECTION 4 – SYSTEM DESCRIPTION 

General 

 
The CMH air compressors are semi-packaged, air cooled units designed for power take-off applications.  
Each unit is designed to operate at ambient temperatures from - 10

°

F to 125

°

F (-23.3

°

C to 51.7

°

C).  For 

the actual delivery of each unit at its rated operating pressure, refer to the typical General Data Decal 
supplied with each unit, and to the table in Section 5. 
 
The unit includes an oil flooded, rotary, screw-type air compressor, a compressor inlet system, a capacity 
control system, a compressor lubricating oil system, a compressor discharge system as well as basic 
instrumentation.  The compressor inlet system includes an air intake cleaner with a service indicator.  The 
capacity control system includes a pressure regulator linked to a compressor inlet unloader valve.  The 
compressor lubricating oil system includes an air-cooled type oil cooler, an oil filter, and oil control valve 
and an oil separator tank and air receiver.  The oil cooler is of the fin and tube-type construction that 
requires forced draft cooling air.  Basic instrumentation includes compressor discharge air pressure and 
temperature gauges, and air cleaner restriction indicator. 
 
The enclosure cabinet, in which most of the components are mounted, is of heavy gauge sheet steel and 
is equipped with easy opening access panels for performing routine maintenance functions.  Most routine 
service can be performed without removing any panels. 
 
Compression in the screw-type air compressor is created by the meshing of two sets of helical rotors 
(male and female) on parallel shafts enclosed in a heavy-duty cast iron housing with air inlet and outlet 
ports located at opposite ends.  The male rotor has four lobes, 90 degrees apart and the female rotor has 
six grooves 60 degrees apart.  The grooves of the female rotor mesh with and are driven by the male 
rotor.  Thrust taper roller bearings at the rear of the air end prevent longitudinal movement of the rotors.  
As rotation of the compressor occurs, the rotors unmesh and free air is drawn into the cavities or pockets 
between the male rotor lobes and the grooves of the female rotor.  The air is trapped in these pockets and 
follows the direction of rotation of each rotor.  As soon as the inlet port is closed, the compression cycle 
begins and the trapped air is directed to the opposite or discharge side of the rotor housing.  As the rotors 
mesh, the normal free volume of air is decreased and the pressure increased until the closing pocket 
reaches the discharge port.  Cooled lubricating oil is admitted to the compressor by being injected, in 
metered amounts, directly into the rotor housing so that it passes on with the air being compressed.  This 
removes the heat of compression to a large degree and results in a relatively low, final discharge air 
temperature. 
 
Since the CMH Series compressor is of the positive displacement type, an air flow control system must be 
provided to regulate the volume of air passing through the compressor to match the amount of service air 
required by the customer. 
 
Constant speed control unloads the compressor at a predetermined pressure while the driving unit 
continues to operate at full speed.  This is accomplished by an air operated regulator closing off the intake 
to the compressor in an infinitely variable or stepless manner through the inlet unloader valve. 
 
The discharge air pressure can be controlled between 77 and 200 psig (531 to 1379 kPa) by simple 
readjustment of the speed and pressure regulator adjusting screw.