If your compressed air freezes in the cow shed in winter, it is because water remains in the air and condenses where the pipe runs through the cold. A refrigerated dryer, like the one built into the K 75, gives a dew point a few degrees above zero, which is enough as long as the whole network stays frost-free. As soon as a pipe crosses an open-sided cow shed or runs outside to reach a gate, you need a desiccant dryer, whose dew point goes well below zero.
Choosing the compressor for the whole farm is covered on our page on the compressor for dairy farms and milking robots. Here we deal with water and cold.
Where does the water in compressed air come from?
The compressor draws in the farm's air, along with its humidity. A cattle building is a damp place: the animals' breath, washing, manure. By compressing the air, the compressor concentrates that water into a smaller volume. While the air is hot, the water stays as vapour. As soon as it cools, in the receiver and then in the pipes, it condenses.
As an order of magnitude, a compressor delivering around 1 m³/min day and night can produce more than 10 litres of water a day in hot, humid weather, and less in winter. Our condensate volume calculator gives the figure for your flow, temperature and humidity.
This water has three effects on a milking robot:
- It wears the valves and cylinders of the arm and the gates, which stick and leak.
- It carries rust and sludge from steel pipes into the robot.
- It freezes in pipes and cylinders exposed to the cold. A pipe that freezes up stops the robot just like a compressor failure.
The dew point, the only figure that matters
The pressure dew point is the temperature at which the water left in the air appears again. Air with a dew point of +3 °C stays dry as long as it does not drop below +3 °C. The rule: start from the coldest point of the network and choose a dew point clearly below it. Our guide to the pressure dew point explains the idea in detail.
Refrigerated or desiccant, the step-by-step method
Step 1, map the network. From the compressor to the robot, then to each sort gate, automatic gate or scraper. Note where each pipe runs.
Step 2, find the coldest point. The robot room is usually temperate. But a pipe running along the cladding of an open-sided shed, a gate cylinder on the outside or a drop to the collecting yard can spend several days below zero in winter.
Step 3, choose the dryer.
| Coldest point of the network | Recommended dryer |
|---|---|
| Always above +5 °C (plant room, heated robot room) | Refrigerated dryer, built into the K series |
| Close to 0 °C at times | Refrigerated dryer, insulated pipes, drains at the low points |
| Below 0 °C (open-sided shed, outside pipe) | Desiccant dryer, with filtration upstream |
A refrigerated dryer cannot go below 0 °C, as the water would freeze in its heat exchanger. Only a desiccant dryer gives a sub-zero dew point.
Step 4, add the purge air. A desiccant dryer takes part of the dried air to regenerate its desiccant. The dryer's data sheet gives that share. Add it to the demand.
Example for two robots (guide values): 700 l/min of demand, 1,050 l/min with the margins of 25% for safety and 20% for expansion, as in our configurator. If the desiccant dryer uses around 15% of the air for regeneration, the compressor must deliver about 1,050 × 1.15 = 1,208 l/min. The K 75, with its 1,100 l/min at 8 bar, is no longer enough. The K 110 (1.7 m³/min) covers this demand. This percentage is only an example: use the one on your dryer's data sheet.
Drying only the cold branch
Often only a small part of the network is exposed to frost: the pipe to two sort gates or to a scraper. Rather than drying all the air with a desiccant dryer, you can keep the compressor's refrigerated dryer for the robot and fit a small desiccant dryer on the cold branch alone. The flow to dry is then small, and so is the purge air. Our technicians look at this set-up with you, including after a 4-in-1 that already dries the air once.
With a standalone compressor such as the S 75, choose the dryer separately: a refrigerated dryer sized for the power, or a desiccant dryer for an exposed network.
Laying pipes that do not freeze
- Fall and low points. Give the pipes a slight fall towards a low point fitted with a drain, and take the drops to the equipment from the top of the main pipe.
- Automatic drains. An automatic condensate drain on the receiver, at the dryer outlet and at every low point. A drain fitted in the cold must itself be protected from frost.
- As little length in the cold as possible. Route the pipes through temperate areas and keep the sections inside the cow shed short.
- Insulation. An insulated pipe slows down cooling but does not prevent freezing in a hard frost. It complements the dryer; it does not replace it.
Our article on water in compressed air covers condensate draining and treatment in detail.
Air quality for the robot
Our compressors are oil-lubricated. Carried-over oil is captured by the outlet filtration, and the K series supplies dried and filtered air that suits the robot's cylinders and valves. If the air touches the teat cups, the milk circuit or the inside of the milk tubes, add fine filters and an activated carbon filter at the point of use. The air class to aim for under ISO 8573-1 is set with our technicians and the robot installer.
Condensate on a farm
Condensate contains oil. Do not send it to the slurry store or into the washing water from the milking parlour. Collect it with an oil-water separator and have it treated.
To find out which compressor and dryer suit your network, enter your equipment in the configurator and send us a simple sketch of the pipework with a quote request.
For your trade: Air compressor for dairy farms and milking robots.