After the sledge, vice and vise-grip, an air compressor is of the most regularly used tools in the agricultural workshop – yet it is often overlooked. Typically day-to-day jobs include inflating tyres, blowing down machinery or operating pneumatic tools – like (air) impact wrenches or paint-spraying equipment. A typical on-farm compressor will be driven by a tractor’s PTO, an electric motor or an engine. A crankshaft is connected to one or more pistons; these ‘pump’ air from the atmosphere through valves into a tank, where it is stored under pressure. Drive from the power source can be either direct or via a belt(s). Single-cylinder designs are the most cost-effective; twin-cylinder versions tend to be quieter and smoother. Twin-cylinder compound models (where one cylinder feeds the next) tend to be more efficient, producing more air and/or higher pressure for the same power consumption. Single-phase (electrical) power supplies can limit potential compressor size but, if power supply is an issue, some manufacturers offer twin-motor, twin-pump units. In this configuration one motor starts – then, after a few seconds, the second motor kicks in. This helps to reduce start-up curren...