“How good is your plate cooler?”

That was a question that Tom Ryan of Teagasc asked me last year. He was one of the speakers here on farm when I held my annual monitor farm public meeting.

“It could be better” I replied. I knew that if I did a full evening milking into an empty bulk tank, without turning on the bulk tank, the temperature would be around 24°C. The ideal operating temperature range is 2°C to 5°C warmer than the water temperature. So, in the next few days I began to investigate.

Using an electronic probe thermometer that I use for reading soil temperature, I measured the temperature of the water as 12.8°C. Next, I needed to establish the flow rates. There is probably an easier way to do this, but I just used the stopwatch on my phone and a bucket and simply timed how long it took to fill a bucket.

This was a little messy but worked. I disconnected the water pipe from the cooler and timed it as 17 seconds to fill the bucket. Then, while milking, I put the milk pipe into the bucket and timed how long it took to fill (once the pump at the back of the pit cut in). It filled in 8.8 seconds.

So, the picture starts to become clearer:

  • The milk flows at 118 litres/min while the water flows at 61 litres/min.

    • That went some way to explain why the inlet water temperature is 12.8°C and the outlet milk temperature is 24°C.

    Next, I turned my attention to the plate cooler itself. When I looked up the specifications, I saw that while it is a good size with 48 plates, it was only capable of handling 53 litres of milk per minute. A couple of phone calls later I got the cooler changed to a much bigger model capable of handling the flow from the milk pump.

    Water flow

    The next challenge was to increase the water flow. The recommended ratio is 2:1 of water to milk. This means I need a flow rate of 236 litres/min.

    It became clear very quickly that no well pump could achieve this. I needed to come up with a solution: a storage tank and a wash down pump or similar. I took a look at the wash down pump that I had already fitted in the parlour. It is a 3HP model and is rated at almost 300l/min.

    I also took a look at an older model that I had taken out some time earlier because it was giving trouble. It is rated at 2HP with an output of 125 l/min. Further investigation revealed it was just the capacitor that had blown and would be a cheap fix.

    I decided to go for it (pumps aren’t cheap), but I also fitted a 250 litre pressure vessel. The pressure vessel holds about 120 litres of water and discharges it as fast as the pipes will allow.

    I did all the plumbing myself using 40mm and 50mm pipes. A 50mm solenoid valve was used to switch on and off the water as the milk pump cuts in and out during milking.

    A 3 second delay was incorporated into the water valve to increase efficiency. I haven't measured the new water flow rate, but the milk is now being cooled to 16.7°C which is 4°C above the water temperature, which is within the ideal operating temperature range. My efforts should stack up to considerable savings in the electricity bill.

    I would like to extend a big thank you to Eugene Casey and Bertie Troy (DairyTech) for their help.

    The next open day here on Tom’s farm is scheduled for 11am on October 9th. All are welcome.