Compressors, Vacuum Pumps, Air Dryers, Air Makeup

Thumbnail descriptions of various kinds of equipment that move air. September 20, 2008

Reprinted with permission from MLS Machinery, Inc.

Compressors are not specific to the woodworking industry. They can be found in garages or wherever air is required. Most machines require air in some form - even small hand tools that are used in factories are air operated. Compressors normally sit on a tank, also known as a reservoir, which could be 120, 240, 360 gallon, etc. A reservoir is just a holding area for the compressed air.

Compressors traditionally come in two types - one is called a screw compressor, which does not need a tank, it pumps air directly to the line where it is required. It is very efficient and a much quieter machine but very costly to repair and processes air in a manner different to a standard compressor. The standard compressor which you see to pump tires, etc. is called a piston style or reciprocating air compressor. It works very similarly to a car engine. Most mechanics that repair cars can repair these units. They work on cylinders, most of them being two cylinders or four with pistons that basically make air and pump it into the reservoir. They come in different horsepowers, depending on the application - they'll come as low as 1 HP and can go up to 300 HP or larger.

Vacuum pumps are used on machines that require a part to be held down while some work is being done on the part without a clamp that can hinder the process. Vacuum pumps are used on CNC routers and point-to-point boring machines to supply vacuum to a vacuum hold down table or vacuum pods. The larger the pump, the more vacuum is supplied.

Air dryers are used mainly to dry the air coming from a compressor. There are numerous types of dryers, the most common being the refrigerated dryer that cools the air using refrigerant to remove the moisture content. The dryer is hooked in line after the compressor and a good rule of thumb when sizing a dryer is approximately 4 CFM per every HP of compressor. Therefore a 25HP compressor should have a 100 CFM dryer attached to it to remove the moisture in the warm air provided by the compressor.

Air make up systems The law states that for every cubic foot (CFM) of air you remove from a building you have to replace it with the exact amount of (CFM). A perfect example is the case of an exhaust fan on a spray booth. This operation takes large amounts of air out of the building. If the air was not replaced this could cause negative pressure in the building and could potentially cause collapse if the air removed was not replaced. Most air make up units are mounted on the roof of the building and will use some form of gas (natural gas) to provide the air required.

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