Eight air compressors, scored on the air they actually deliver

How the score is calculated

We have not run any of these machines, and we do not present anything as if we had. The score comes from four measurable criteria: air delivered at 7 bar 40 percent, price per delivered l/min 25 percent, sound power LwA 20 percent, weight 15 percent. Each value is placed on a 4 to 10 scale against the other machines in the panel.

When a maker does not publish a figure, or publishes it ambiguously, that criterion drops out and the remaining weights are renormalised. Below 60 percent of the scale, or without air delivered at 7 bar, no score is calculated. Two machines are in that position, and their pages say why.

The intake trap

A compressor nearly always advertises its intake: the air the pump draws in, measured at no pressure. Once that air is compressed to 7 bar, far less is left. In this panel, delivered air is 27 to 36 percent of intake for five machines out of six. The Scheppach HC51V draws 220 l/min and delivers 65.

The Mecafer Fifty is the exception: 126 l/min delivered from 230 drawn in, or 55 percent. That is the figure Mecafer publishes on its page and its datasheet, and we use it as published. It puts this model top of the ranking. If you buy it for that figure, bear in mind how far it stands from the rest.

Makers do not all measure at the same pressure either. Metabo quotes its effective delivery at 80 percent of maximum pressure, which is 6.4 bar on an 8 bar machine. The lower the pressure, the more flattering the flow: that figure does not compare with a 7 bar one, and we do not score it.

Noise: only one figure compares

Guaranteed sound power LwA appears on the label European rules require on compressors. It is the only noise figure we score. Sound pressure, often printed large on the tank, depends on distance and load: the Scheppach HC51Si's 60 dB(A) is measured at 7 metres and 25 percent load, and its guaranteed sound power is 87 dB(A).

Before you connect the first tool

• Never point the blow gun at skin. Not to dust off clothes you are wearing, not as a joke. Compressed air can enter the skin and cause a serious injury.
• Eye and hearing protection. A blow gun throws chips and dust at eye level, and most of these machines exceed 90 dB(A) of sound power.
• The tool's pressure, not the tank's. Set the regulator to the pressure stated on the tool. Never adjust the pressure switch or the safety valve.
• Drain the tank. Condensed water collects at the bottom and corrodes the steel from inside. Open the drain valve after use, with the tank depressurised as the manual describes.
• A long hose rather than a long extension lead. A lead that is too long or too thin drops the voltage when the motor starts. Manuals advise bringing the compressor close to the socket and running a longer air hose.