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Changes to the Rating and Advertising of Home/Workshop Air Compressor Electric Motor Horsepower Values

Changes to the Rating and Advertising of Home/Workshop Air Compressor Electric Motor Horsepower Values

After many years of rating and advertising air compressor horsepower values based on “Peak” or “Maximum Developed” testing criteria, a group of manufacturers specializing in providing the typically smaller, home/workshop type air compressors will change over to rating and advertising the horsepower testing criteria called “Continuous” or “Running” horsepower. The latter rating system is now widely used in the industrial air compressor market and this move will commonize horsepower rating systems between both markets.

The old “Peak” or “Maximum Developed” testing/rating system generally provided higher numeric values for horsepower ratings than the “Running” system for the same motor. To assist in the understanding and transition to the eventual lower value, single common “Running Horsepower” system by December 2005 (initially indicated as March 2005), many manufacturers and retailers will, for a period of time, show numeric values of both systems on their products and in advertising.

As always, choosing the right air compressor for your identified needs certainly does not depend upon the horsepower rating value alone. Many other factors such as…
1. the maximum air pressure (PSI) developed,
2. the volume (SCFM) of air produced by the pump,
3. the size (gallons) of the reserve air tank,
4. and, the length of time required for recovery of full tank pressure
…will determine the overall performance capability of the air compressor system. Plus, other factors such as voltage, amperage, ease of operation, weight, and storage or portability features need to be considered as well.

Air Compressor Selection Tip No. 1
Determining the amount of “useable air pressure” stored in the reserve air tank is a good idea. A typical air tool needs 90 PSI to operate properly and the outlet air regulator pressure setting is usually set at that value or slightly higher to allow for some hose/fitting pressure drop. Subtract that 90 PSI from the maximum pressure that can be developed inside the reserve air tank. For example, on a maximum 125 PSI system there would be (125-90) or 35 PSI of “useable air pressure” in the compressor tank. On a 150 PSI system there would be (150-90) or 60 PSI or (60-35) 25 PSI more or 70% more “useable air pressure” from the higher maximum air pressure system.

Air Compressor Selection Tip No. 2
Higher maximum air pressure systems also have the advantage of motors designed to restart at a higher pressure point, which is helpful. These compressors “start and stop” automatically at preset pressure points. On a typical lower pressure 125 PSI system the motor will automatically “stop” running at the maximum 125 PSI point and won’t automatically restart until pressure in the reserve tank drops to about 95 PSI which occurs in normal use. 95 PSI is too close to the minimum 90 PSI needed for many air tools and therefore the motor restart and subsequent recharging of the reserve air tank is too late to be of much help. On a typical higher maximum pressure 150 PSI system the motor will restart at 125 PSI or (125-95) 30 PSI higher and well above the 90 PSI needed for the air tool. With the motor and pump running sooner the higher maximum pressure system allows earlier recharging of the tank and even provides for increased or longer actual tool run time.