Just curious as to if I should worry about my bog pipes freezing and cracking over the winter. Or is this not a concern since the slits in the pipes allow room for the ice to expand? Also the entire bog is an ice block so I'm thinking the pipes wouldn't have room to expand and crack. I ask this since my ball valve which is up and out of the bog cracked in half from ice expansion.
depends on if they freeze or not; water won't freeze below your frost line (I know, I know; you're in frigid Wisconsin!) so if your bog is deeper than that (or, your bog is running all the time), you'll be fine. Now, even with slits, if your water freezes, you may well get cracking. Hard to say how much this would effect your bog, though, since you 'cracked' the pipe anyway with slits. I'd imagine, over time, that any cracked pvc manifolds would still to their job for a long time before you noticed water coming up a lot more on one side over the other and even then, water will still find it's way to the whole bog eventually.
I'd say any pipes with water that freezes, are suspect. That's why many use flex pvc; it's 'flexible', don'tcha know and can take such freezing outward pressure. I know on my sprinkler system (diy), I had some cracking one year because I didn't turn it off before an early freeze got to it, but there was pressure behind the pipe whereas with a bog, there shouldn't be the same kind and none at all if you turn your bog off for winter. For my bog, as noted, I used flex pvc going down to the bottom of my 3' depth bog ( not quite below my frost line here in MI) and then into larger, 4" corrugated drain tile/pipe, so no solid pvc for me to worry about.
