A diaphragm compressor is a device designed to compress or pressurize atmospheric air for storage or immediate use by means of displacement of a flexible membrane or diaphragm. This rather technical definition simply means that a diaphragm compressor is an air compressor the uses the flexing of a rubber or silicone membrane to compress the air rather than a piston system. Conventional air compressors make use of a piston and crankshaft arrangement very similar to those found in a car engine to compress the air. Diaphragm compressors, or membrane compressors as they are also known, use a crankshaft and rod to flex a membrane which compresses air due to the displacement phenomenon.
One of the easiest ways to demonstrate these principles is to consider an example. If an empty plastic syringe is blocked with a finger and the plunger depressed slowly, an increase in tension on the plunger will be felt. This is due to the compression of the column of air in the syringe tube. If a sheet or blanket is held on all four corners by two people and is flapped up and down, a noticeable air current is generated. These two phenomena are the result of air being moved or displaced by a solid object.
In a conventional piston compressor, the column of air in the piston sleeve is compressed in the same fashion as the air in the syringe. When the piston reaches the top of its travel, a valve opens which allows the compressed air to travel into a pressure tank, where it is stored for later use. As the piston moves back down to its lowest point, it draws more air into the cylinder and the process starts again.
A diaphragm compressor achieves the same result by moving a flexible membrane or diaphragm up and down by means of a crankshaft and rod assembly in the same way the blanket is shaken. The resultant air displacement causes compression of the air in a chamber fitted with the same type of valves found in a conventional piston compressor. Apart from the obvious operational differences, the compression cycle remains the same. The diaphragm moves up and compresses the air, which leaves the chamber via the outlet valve. The diaphragm then draws new air into the chamber on its down stroke and the cycle is repeated.
The diaphragm compressor is used in a wide range of applications, from small 1/8 horsepower models capable of producing 50 pounds per square inch (PSI) or less of continuous pressure to massive 6,000 PSI industrial gas compressors. The diaphragm compressor is particularly suited to hobby applications such as airbrush painting and the compression of toxic or explosive gases due to the fact that metal-to-metal friction is kept to a minimum.