The power of a vacuum system motor is commonly expressed in horsepower. This is an inexact term, however, since horsepower will vary under changing conditions such as voltage supply, barometric pressure and at what points and under what conditions exist when readings are taken. Most motor manufacturers publish a nominal horsepower rating for their motors and since central vacuum system manufacturers frequently use identical motors in their most popular models, it would seem that this would make it easy to use this particular rating as a standard. This, however, is not the case since the subdivisions of these designations is of such variety and complexity as to make it of little value to the consumer as a measure of efficiency between two central systems. Therefore, a performance rating based on measurements and values as explained in subsequent sections is of more value than horsepower.

IWL (inches of water lift)

The number of inches up a thin glass tube which a given vacuum motor can pull a column of water is called “IWL” or inches of water lift. This is a common rating system, but can be unreliable as a figure compared directly from specifications of one or more central vacuum system manufacturers. Unusually high ratings may refer to conditions impossible to duplicate in actual installation and may be taken from tests not conducted by the manufacturer of the vacuum motor and may yield ratings higher than would normally be obtained.

A motor’s sealed vacuum power is indicated by IWL as explained above. But a much more accurate picture of the cleaner’s efficiency may be expressed as Working Vacuum since this measures vacuum power in connection with air movement, just as the user experiences it. Sealed vacuum measures only the motor’s capacity, not the air stream, which, after all, is what picks up the dirt.

Galaxie’s GA-100 working vacuum rating is approximately 78.8” of water lift, while air is being moved through a 5/8” opening equivalent to the opening in the average vacuum cleaning tool. This is the most accurate
measure of the power used in actual operation.

CFM (cubic feet per minute)

CFM is an additional measurement of the efficiency of a vacuum motor. It is measured as “the volume of air which passes through a given opening during a one minute period. The size of the opening used in testing will change the rating figure greatly.

To get a maximum CFM reading, the motor must be wide open (2” opening). But, to get a maximum vacuum reading (IWL), the motor must be closed (sealed vacuum reading). However, the motor is never actually used in either condition. Instead, both measurements should be made at the same opening, one used in normal cleaning or about a 5/8” opening (the standard opening in the average vacuum tool).