For a semi-automatic keg washer and filler with one or two heads, a 7.5 kW 4-in-1 screw compressor such as the K 75 is enough in most breweries: it delivers 1.1 m³/min at 8 bar and its 420 L receiver absorbs the purge peaks. An automatic multi-head keg washer, or a keg washer running at the same time as the bottling line, calls for a K 110 instead.
The air needs of the whole brewery, from the brewhouse to the capper, are covered on our page on compressors for breweries and cideries. Here, we focus on the keg washer.
What is air used for in a keg washer?
A keg washer and filler runs a series of short steps: emptying residues, rinsing, washing with caustic or acid, rinsing, sanitising, pressurising and filling. Compressed air has two jobs:
- operating the pneumatic valves that open and close each circuit;
- driving liquids out of the keg between steps, with pulses of air.
Counter-pressure and filling are done with CO2 or nitrogen, not air: oxygen spoils beer. These gases come through their own lines and do not count in the compressor sizing.
The calculation, step by step
Step 1, the keg washer data sheet. The maker gives the air consumption, in l/min or in litres per cycle, and the working pressure, often around 6 bar. If the sheet gives litres per cycle, multiply by the number of cycles per hour and divide by 60.
Step 2, the peaks. Purges use air in bursts. The average over an hour is low, but for a few seconds the washer draws much more. The receiver supplies that peak, and the compressor refills it afterwards.
Step 3, the other machines. Add whatever runs at the same time: filler, capper, brewhouse valves, blow gun.
Step 4, the margin. Add 25 %, as our configurator does.
Example of a brewery washing and filling its kegs on a two-head washer (indicative figures, replace them with those on your data sheets):
- two-head keg washer and filler: 2 × 120 l/min = 240 l/min
- brewhouse valves: 50 l/min
- blow gun, used in bursts and counted at 50 %: 75 l/min
- total: 365 l/min, or 460 l/min with a 25 % margin
The K 75 delivers 1,100 l/min at 8 bar: it covers this need with plenty of reserve, and its 420 L receiver exceeds the volume our configurator suggests for this flow, about one litre for every 3 l/min of demand.
Which model for your keg washer?
| Installation | Suggested model |
|---|---|
| Manual or semi-automatic washer, one or two heads | K 75, 1.1 m³/min at 8 bar, 420 L receiver |
| Two-head washer and bottling on the same day | K 75 if the total with margin stays below 1,100 l/min, otherwise K 110 |
| Automatic inline washer, several heads | K 110, 1.7 m³/min at 8 bar, or K 150, 2.2 m³/min |
All models in the K series are variable speed. Between two kegs, while the washer waits, the compressor slows down instead of running idle.
The quality of the air entering the keg
The air that drives the valves touches nothing: the dried, filtered air from the K series is fine for it. The air that purges the keg, however, touches the inside of a food container. Our compressors are lubricated: add fine filters as close as possible to the washer, on the purge line. The air class to aim for under ISO 8573-1 is set with our technicians and the washer maker. Our ISO 8573-1 air quality guide explains how to read these classes.
Traps specific to keg washers
- Liquid backflow. If air pressure drops during a purge, cleaning solution can flow back towards the air line. Check that there is a non-return valve on the washer's air inlet.
- Pressure too tight. If pressure falls below the data sheet value during purges, the keg stays wet. Set the compressor to 8 bar and place the washer close to the receiver or a buffer tank.
- Humidity in the washing area. Do not put the compressor next to the washer: install it in a dry, ventilated room, away from splashes. Our article on the compressor room gives the rules.
- Condensate. It contains oil: do not send it down the drain with the wash water. An automatic condensate drain and a collector solve the problem.
- Filter servicing. A saturated fine filter costs pressure and no longer protects. Replace the elements at the maker's interval. The compressor itself has its first service at 500 hours, then every 1,500 hours.
For the final choice, enter your machines in the configurator, then send us your keg washer data sheet with a quote request.
For your trade: Compressor for breweries and cideries.