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Buying a compressor. Things you need to know!Buying an air compressor: This can be quite complex. I'd like to simplify the process for you, by providing useful information to help you in your search. Unless you've spent a lot of time investigating or working with them, it is possible to overlook something that is key to your compressor needs and in the long run, that can be quite expensive. I have prepared the following questionnaire / check list for you to use, to gather information from the various compressor manufacturers you talk to, to help you decide which company, type of compressor, or feature(s) provides you the best value. Your compressed air requirements If you haven't yet determined your total CFM requirements are, and at what pressure you need that compressed air delivered, you can't be expected to select a compressor that suits. You really must do this first. Please see these links for further information:
Remember, when you're sizing your compressor, that 1 HP of compressor output generates about 4 CFM of compressed air at 90 PSI. This is the accepted wisdom for air compressors over 10 HP. For DIY compressors under 10 HP, you must rely on the figures provided by the manufacturer or "guestimate" that you're getting around 2CFM of compressed air per HP @ 90 PSI. Remember too that you can expect to lose about 10% of your overall air production through compressed air misuse or leaks, and through pressure drop in the system. Ensure that you've allowed for this. Don't forget where you are planning to be in 5 years regarding compressed air-related demand. Allow for expected growth.
Whether your compressor should be a continuous run style, or one that starts and stops based on the pressure cycle, may be answered by your demand requirements. If it isn't clear cut, talk to the manufacturers about their benefits for a compressor that fills a reservoir and stops until low pressure signals a start, or one that runs continuously, but only compresses air as the demand is there. Field portable units, which often run on gasoline or diesel, are usually continuous run, as the need to start and stop a fossil fuel motor every few seconds is very negative to the motor. Are you planning to take it with you, or is it a fixed installation? While most plants rely on fixed installations, there will be many applications for portable air compressors too. If that's your choice, you need to discuss with the vendors the methods of portability; is the air compressor carried, come already installed on a wheelbarrow or cart, is the compressor itself wheeled, trailered, etc., etc.? You discuss this with the compressor sales outlet based on your expected needs. Available power supply Regardless of the type of compressor you purchase, it will have to have a power supply. If it's to be installed in a plant, what voltages or amperages do you have available? To get the volume of air you need, will you have to upgrade your electrical system? If it's a portable style of compressor, do you want it powered by gasoline, diesel or perhaps propane? Any other options, depending on where you are in the world?
Your compressed air supply and pressure requirements will allow you to select manufacturers that actually make compressors of the capacity you require. The power supply will further narrow the list of vendors to those that can provide a unit that runs on the power you have available or that you choose to use. Regarding electrically driven compressors, higher voltage units sometimes generate compressed air at lower cost. Ask about the voltages available from that vendor, and your benefit as it pertains to lower operating costs depending on that voltage. Perhaps you might find that a propane unit offers lower operating costs than gasoline if you need a portable unit. Determine from each vendor the cost to generate a fixed amount of compressed air – perhaps the cost to compress and supply 10,000 CFM at 100 PSI, based on their equipment’s efficiencies and the power costs where you are to generate that air, to help you compare energy consumption costs for each. Ask how they measure this with their units? Here's more information on buying a compressor. To top
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