A 1 inch impact wrench uses around 600 l/min at 6.3 bar while it runs, as a guide. You therefore need a compressor that delivers at least that flow, on a receiver that absorbs the peaks: a compressor of about 1 m³/min, such as the E 75 HP or the K 75, runs one wrench continuously and two wrenches in turn.
It is the hungriest tool in an agricultural machinery workshop: the one that takes off tractor wheels and the big bolts on trailed implements.
The calculation for one wrench
Start from the consumption in your wrench's manual. The usual order of magnitude is 600 l/min at 6.3 bar.
An impact wrench works in bursts: a few seconds per nut, then a pause. To size a whole workshop, it is counted at 50% thanks to the receiver, so 300 l/min. But while it is running, it really does draw 600 l/min. Two rules follow:
- The compressor must deliver at least the wrench's flow, otherwise pressure drops while you undo a full wheel.
- The receiver must cover the moments when several tools run together.
The calculation for two wrenches at once
Two 1 inch wrenches running together need 1,200 l/min. Here is what the receiver does, starting at full pressure and falling to 8 bar.
With the E 75 HP (1,050 l/min, 300 L receiver, 12.5 bar):
- Flow shortfall: 1,200 - 1,050 = 150 l/min.
- Receiver reserve between 12.5 and 8 bar: 300 × 4.5 = 1,350 litres.
- Running time: 1,350 ÷ 150 = about 9 minutes of both wrenches running non-stop.
With the E 75 in the 12.5 bar version (900 l/min, 180 L receiver):
- Flow shortfall: 1,200 - 900 = 300 l/min.
- Reserve: 180 × 4.5 = 810 litres.
- Running time: 810 ÷ 300 = under 3 minutes.
Since wrenches run in bursts, these times are plenty in most workshops. Above all, the calculation shows the difference between a large and a small receiver.
Which compressor?
| Use | Recommended model |
|---|---|
| One 1 inch wrench, occasional use | E 75, 0.9 m³/min, 180 L receiver, 8 or 12.5 bar |
| One or two 1 inch wrenches, large tyre inflation | E 75 HP, two-stage, 1.05 m³/min, 300 L receiver, 12.5 bar |
| Air all day, wrenches and painting | K 75, 4-in-1 screw, 1.1 m³/min at 8 bar, 420 L receiver, built-in dryer |
The E series piston compressors are designed for intermittent use. If the workshop runs wrenches, blow guns and greasing from morning to night, a screw compressor such as the K 75 handles continuous duty. A small 0.6 m³/min screw compressor, such as the S 55, is only just enough for one 1 inch wrench: it has no receiver and leaves no margin.
If you also remove truck wheels across several bays, see our page on truck workshops.
Traps that cost you torque
Hose and couplings. This is the most common reason a wrench "lacks power". A hose that is too narrow or too long, or a quick coupling that is too small, drops the pressure at the tool, even with a large compressor. Use the hose size and coupling stated in the wrench's manual. See our connection hoses.
Pressure measured in the wrong place. The compressor gauge does not tell you what reaches the wrench. Measure at the wrench inlet while undoing a nut: that is where you need 6.3 bar, or the value in the manual.
Water and oil. Water from the receiver damages the hammer mechanism. Drain daily or fit an automatic drain. Lubricate the wrench as its manual says: a few drops of oil at the inlet, or a lubricator on the tool line, never on a paint line.
Piston compressor maintenance. A slack belt, a clogged filter or a worn valve reduce real output. Our article on the piston compressor maintenance schedule gives the intervals.
List your tools in the configurator, or send us a description of your workshop with a quote request.
For your trade: Compressor for agricultural machinery workshops.