Some people say soda. Others call it pop. Another group might refer to it as a soft drink. But we all know what it means. The differences in regional dialect vocabulary in the United States reveal a wide and diverse variety of terms for the ways we all use different words or phrases to say the same thing.
Terminology differences for food and drink are inconsequential. In an industrial setting, however, measurements and instruments determine exact specifications. The slightest of errors can have dramatic (and expensive) consequences, which makes it critical that all parties know exactly what the other means.
When dealing with compressed air systems, misunderstandings can arise due to a variety of delivered flow level terminology. For example, people address CFM (cubic feet per minute) levels in many different ways. Three common CFM terms and how they can differ are:
- SCFM – Standard Cubic Feet per Minute flow is measured after the compressor and then referred back to STP (standard temperature and pressure) conditions. The specified flow, according to this form of measurement, gives an accurate indication of what the customer will receive. It is important to also specify the reference conditions other than inlet conditions while calculating SCFM.
- ICFM – Inlet Cubic Feet per Minute is the volume of measured gas, in this case air, at the inlet point to a machine; with this form of measurement, the internal losses are not taken into consideration.
- CFM (FAD) – Free air delivery cubic feet per minute is volume flow rate of gas compressed and delivered at the standard discharge point; with consideration of the atmospheric conditions of the site, all the losses are taken into account and this will determine the net usable air available to you.
On an elementary level, an air compressor is a box, with air going in one end and coming out the other. One person may use one of these terms to mean inlet flow, the measured airflow going into an air compressor intake. Another might use delivered flow, or the measured flow after the air has been physically compressed. Because there are some inherent pressure losses as part of the physical process – inevitable pressure drops at piping, losses during the transition from suction to discharge, the output of the machine, and the discharge of condensate that is a byproduct of compressing air – the outlet flow is going to be lower.
Every machine is different. While it can be expected that as much as 3 percent volume will be lost as part of the compressed air process, it’s important to consider and determine the pressure drops and losses that will occur within the air compressor as part of the process, and the terms each parties associates with air pressure going in and air pressure coming out. Make sure each party involved in quoting and sizing an air compressor has the same expectations, regardless of the terms and words they use. This will ensure that the customer receives the flow they need.
What other interchangeable compressed air terms do you find confusing? Have you used one term only to learn that a customer or industry peer expected something else? Let us know in the comments section below, and we’ll address it in future posts.
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