By: Frank Caprio | On: April 13, 2017
Today’s topic is air compressor hoses, and the importance of understanding temperature considerations. Air compressors have many uses in today’s world, as compressed air is an economical means to store energy. This energy may be used to power a wide variety of pneumatic equipment: air cylinders, jackhammers, spraying equipment, etc. However, compressed air exhibits certain properties that should be considered when selecting flexible hoses for the application, and one of these properties is temperature increase.
As a gas is compressed, heat is created as the molecules crash into each other more frequently. Unless this heat is dissipated, the compressed gas carries this heat out of the compressor and into the piping system. In smaller compressors, this heat usually does not present a problem. However, larger air compressors – such as those used on construction sites – can create significant amounts of heat. These larger compressors must provide a sufficient volume of air to run all of the equipment on the jobsite, and often have 2” or 3” NPS connections on the compressor outlet.
The flexible air compressor hoses that connect to these compressors are referred to as “bull” hoses, and are typically a wire-reinforced rubber hose with an oil-resistant tube and an abrasion-resistant cover. These rubber hoses work quite well for most compressed air applications, and are supplied with specially designed (“ground joint”) fittings and interlocking clamps that prevent sudden fitting detachment. Oil-based lubricants are added to the compressed air, in order to keep the compressor and the pneumatic equipment connected to it running smoothly.
Occasionally, the heat generated by the compressor can reach sufficient temperatures where it begins to degrade the rubber hoses attached to it. Rubber hoses that have been exposed to excessive heat will exhibit signs of impending failure, including cracked covers, hardening of the inner tube, or hoses taking a “set”, where they remain bent even after being taken out of service. Exposing rubber hoses to excessive heat not only reduces the service life of the hose, it is also a safety concern. Compressed air can be very dangerous if a hose fails catastrophically, as an unrestrained hose may “whip” violently or cause a fitting to blow off of the end. There are numerous ways to mitigate these types of failure, but they do not prevent the root cause: high operating temperatures.
In applications where compressed air is being conveyed at high temperatures, a corrugated metal hose should be considered as an option for several reasons.
- First, metal hose prevents the temperature-induced failures listed above that may occur with non-metallic hoses.
- Second, metal hoses have positive coupling retention. Welded-on end fittings prevent any chance of coupling blow-off, and do not require periodic tightening like the interlocking clamps used on rubber hoses. This adds an extra level of safety to the application.
- Third, a corrugated metal hose will dissipate the excess heat very quickly. Corrugated hose has a very high surface area that serves to cool down the compressed air by radiating excess heat from the media. This helps protect rubber hoses that may be located downstream from the bull hose.
It is important to remember that when a metal hose is being used at elevated temperatures, the alloys used for the hose, braid, and fittings must be able to safely convey the pressurized air at the specified temperature. Consult our Temperature Derating Chart for details.
Remember, even one length (25 feet or so) of corrugated metal hose connected directly to the compressor can help protect all of the rubber hoses connected to it downstream. It’s a small price to pay for increased service life, added safety, and peace of mind.
Call Hose Master’s Inside Sales team at 800-221-2319, and they will help you find the right hose for your application.
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