Controlling pressure buildup in air motors

By Staff -- Plant Engineering, 5/1/2000

In regard to the "Simple Solution" from C.R. Barr, "Controlling pressure buildup in air motors" (PE, January 2000, p 14), the method for controlling pressure buildup in idle air motors by drilling a 1/8-in. hole in the air line would be a significant waste of power.

This size hole will dissipate between 5-7.5 hp of compressed air, depending on the normal working pressure, whenever the air motor is in operation. This amount is a huge and costly penalty. In addition, this air leak will reduce the power being delivered by the air motor, unless the air line pressure is increased, in which case, the air loss will increase even further!

A simple, cost-effective, and lasting solution would be to install a shut-off valve with integral downstream bleed to control the air motor while assuring zero air loss, power waste, or performance penalty, while effectively eliminating all unwanted "inch over."

Kilowatt consumption is one of our biggest operating expenses, and we must always seek means to reduce or eliminate power waste.

-H. Paul Laesch

C.R. Barr's reply: The suggestion from Mr. Laesch to install a shut-off valve with an integral downstream bleed would certainly do the job, and I make that comment based on the assumption that the bleed would be closed when the valve is opened. That being the case, it is certainly a workable solution.

It is true that the air that would flow out through the drilled hole in the piping to the air motor would represent a loss of air. However, that air loss would be of minor concern when considering an air motor in a situation running only on an intermittent basis. Also, depending on the size of the equipment, pressures, and pipe size involved, the question as whether or not the drilled hole would materially affect operation of the air motor is arguable.

I agree with Mr. Laesch's comment that energy costs must be considered in the operation of any plant or facility, but sometimes compromises must be considered in the interest of expediency, or are made because of other restrictions, such as available machine downtime, lack of money, safety requirements, or production requirements, just to name a few.

-C.R. Barr, Everett, WA