Nicky,
these are not the ones with the balls, I wont use those things anymore, I think these are called Cattlemasters, they are 7 feet long, we put valves in them that have two stages, one when a little water is gone, and two when all of the water is gone the valve is wide open and fills the tank as fast as the water pressure allows. They will get a buildup of ice on them when it is -20 but it comes off easy and you have had water moving in the lines all of the time so no lines freezing up. You can also set them up with a thermostat so the water only moves when it hits the temp you set it on. When we had Mirafounts we always had to drop the float level low enough that the balls did not fill the hole or tie the balls down to get cattle to figure out how to drink. Then at 20 below if you have the balls filling the hole, water dripping from the cows freezes the balls shutting the hole and then everything freezes up. I threw the tops away and put mineral in the Mirafounts.