Buyers Guide.

While you may think an air compressor is only for pumping up your tyres, many models can also be used to drive paint sprayers, nail guns, wrenches and a host of other useful tools. So before you start, think about whether you only really need a compressor for your car and the kids' bikes, or whether you want to use it for all its other possible applications.

If tyres are your main concern, go for a compact air compressor, which will also be able to handle light tasks such as powering small spray guns, but not a lot else. These tend to be relatively cheap, and if you plan to keep one in the back of the car for emergencies, can now be found with torches and flashing emergency beacons built-in for roadside punctures. Of course, if you want to use your compressor for jobs around the house, look for models that have an AC adapter, as well as an adaptor for the cigarette lighter in your car.

If you want to power proper air tools, however, you'll need a piston-type compressor with a tank to store compressed air. With this type, the compressor's motor shuts off when the pressure in the tank reaches a specified level, and as air is used up the pressure inside drops and the motor restarts to build the pressure back up. There are two kinds of piston compressors: single-stage and two-stage, but with both you should always choose a machine with pressure settings that you can adjust according to your needs.

Single-stage compressors have one piston that compresses and delivers air (normally at pressures below 150psi) to the storage tank. Single-stage models are more than adequate for most home users, although heavier users may wish to consider a beefier two-stage machine, where the first piston compresses the air and pushes it through a check valve to the second piston, which then compresses the air further and delivers it to the storage tank. Two-stage compressors are the best choice for continuous or industrial use (like tractor tyres, for example), as they tend to last a lot longer under heavy loads and can create pressures way above the 150psi mark.

When it comes to working out the benefits of different manufacturer claims, HP ratings are a measure of the power the compressor motor produces, so the higher the HP, the greater pressure the machine can deliver. Non-industrial compressor motors range from 1.5 HP to 6.5 HP. Compressor storage tanks are rated in gallons, with larger tanks storing more compressed air at higher pressures (measured in cubic feet per minute, or CFM). If you want to use your compressor to power air tools, these figures are very important, as most air tools have specific requirements for volume and pressure. When choosing a compressor, think about the tools you want it to operate, choose the tool that requires the highest CFM at the highest psi and add 50% to the required CFM to be on the safe side. So, if a tool requires 4 CFM at 90 psi, go for a compressor that delivers at least 6 CFM at 90 psi.

If you're not a professional user (in which case you know all this already), always buy an oil-free compressor with sealed bearings, which will need a lot less maintenance than an oil-lubricated machine. While you will find gas-powered compressors easily available, these can only really be recommended if there is no chance of finding an electricity outlet near where you want to work, as you should never use a gas-powered machine in any kind of confined or unventilated situation.

Questions and Answers.