A milking robot stops as soon as the air pressure falls below the minimum in its manual. To keep milking going through a breakdown or a service, install a second compressor able to cover at least the robots' consumption, roughly 300 l/min per robot as a guide, and a low-pressure alarm. For two robots, two K 75 units taking turns, or a K 75 with an S 55 as backup if your robots use little air, are the most common set-ups.
Sizing the main compressor is covered on our page on the compressor for dairy farms and milking robots. Here we look at what happens when it stops.
Why a backup compressor on a milking robot?
In a conventional milking parlour, a compressor failure delays milking. With a robot, it stops milking altogether, day and night, with nobody on site to notice. The cows wait in front of the box, those due to be milked go past their interval, and the herd's routine falls apart. The longer the stoppage, the more it costs in milk and in stress for the animals.
Yet a compressor can stop for ordinary reasons: a high-temperature trip on a heatwave day, a stuck drain, a power cut, a scheduled service. A single compressor, even a new and well-maintained one, is a weak point.
What flow must the backup cover?
Start by sorting the consumers, as in our general article on the backup compressor:
- Critical: the milking robots. Without them, there is no milking.
- Useful: the sort gate and automatic gates. They can be switched to manual for a few hours.
- Can be shut off: the workshop, the blow gun, tyre inflation. They are isolated during the breakdown.
Example for two robots (guide values, to be replaced with those in your manuals):
- Critical flow: 2 robots × 300 l/min = 600 l/min.
- Add a 25% safety margin for leaks and peaks: 600 × 1.25 = 750 l/min.
- The backup must therefore deliver at least 750 l/min at the pressure the robots require.
There is no need here for the 20% expansion margin, as the backup only runs during a breakdown. But if another robot is planned, redo the calculation before buying.
Three possible set-ups
Set-up A, two identical machines. Two K 75 units, each delivering 1.1 m³/min at 8 bar. One alone covers the farm's whole demand. If one stops, the other carries on without anyone noticing, except through the alarm. Each machine has its own built-in dryer, so there is no longer a single weak point. This is the safest set-up.
Set-up B, a smaller backup. A K 75 as the main unit and an S 55 as the backup. The S 55 delivers 600 l/min at 8 bar. With the 25% margin, it covers two robots using up to 240 l/min each (600 ÷ 1.25 = 480 l/min, or 240 l/min per robot), without the gates or the workshop. In our example at 300 l/min per robot it is too tight: the backup must deliver the 750 l/min calculated above, and a second K 75 becomes necessary. The S 55 is a standalone compressor, so connect it upstream of the receiver and dryer, or give it its own dryer.
Set-up C, three robots. A K 110 as the main unit (1.7 m³/min) and a K 75 as the backup (1.1 m³/min). For three robots at 300 l/min, the critical flow with margin is 900 × 1.25 = 1,125 l/min, a little more than the K 75's 1,100 l/min. The K 75 is only suitable as a backup if your robots use about 290 l/min each at most (1,100 ÷ 1.25 ÷ 3). Otherwise, two K 110 units are the right answer.
| Robots | Main unit | Backup |
|---|---|---|
| 1 | S 55 with receiver and dryer, or K 75 | S 55 |
| 2 | K 75 | K 75, or S 55 if the critical flow allows |
| 3 | K 110 | K 110, or K 75 if the critical flow allows |
Compressor hire is no substitute for a backup on site: by the time a hired unit arrives and is connected, milking has stopped. It remains useful for building work, an expansion or a long breakdown of one of the two machines.
How do you set the changeover between the two compressors?
Two machines connected to the same network take turns through their pressure settings:
- Stagger the settings. The main compressor starts at a slightly higher pressure than the backup. If the pressure falls because the main unit has stopped, the backup starts on its own.
- Swap the roles regularly. Every week or every month, make the backup the main unit. Both machines wear evenly, and you know the backup starts.
- Fit isolating valves. Each compressor must be able to be isolated from the network for servicing without cutting the air to the robots.
- A non-return valve on the outlet of each machine stops air in the network flowing back to the stopped compressor.
Our guide on connecting the compressor to the air network shows the valves to plan for.
The low-pressure alarm
The robot already raises an alert when it goes into fault. But by then, milking has stopped. It is better to be warned earlier:
- a pressure switch set a little above the robot's minimum pressure, linked to the farm's alarm dialler;
- fault signals from each compressor relayed to the same dialler, if the installation allows;
- a clear pressure gauge near the door of the room, so you can check at a glance as you walk past.
Test the alarm: close the outlet valve of one compressor during a quiet period and check that the message arrives.
Backup power
A backup compressor is no use during a power cut. If the farm has a generator for the robot and the milk tank, it must also power at least one compressor. Our compressors run on 380 V three-phase, so have your electrician check that the generator can handle the compressor's start-up on top of the robot and the milk cooling. Variable speed models start progressively, which is easier on the generator.
The other weak points
- A single dryer. If both compressors go through one dryer, fit a bypass with valves. The K series 4-in-1 units solve the problem, as each has its own.
- The drain. A stuck automatic condensate drain fills the pipe with water, which freezes in winter. Check it every time you pass.
- Servicing. A robot compressor may run almost continuously: 1,500 hours, the service interval after the first service at 500 hours, is about 9 weeks. Do the servicing while the other machine keeps the milking going. Our guide to screw compressor maintenance gives the steps.
To size your main and backup units, enter your robots in the configurator, then ask for a quote with your robots' manuals.
For your trade: Air compressor for dairy farms and milking robots.