I have what appears to be a Pentair Triton II sand filter. I say "appears" because it doesn't have any label or identifying markings that I can find. But it looks just like one, namely, the wrench, the lid, the diffuser assembly inside, etc. Note that the pressure gauge and air bleed as seen in the photo aren't original.
http://www.pentairpool.com/pool-pro/par ... s-214.htm#
And with pictures of the individual components:
http://www.poolpartsonline.com/p-78-pen ... parts.aspx
The leak is coming from the sand drain plug, part number 17 on the diagram. Water is actually spraying horizontally out of a crack in the side of the hex end of the sand plug, which you can sorta see in the photo.
Pentair used different sand drain plugs in different years of manufacture. The pool dates back to 1978, and I've only lived in the house for about four years, so I don't know the year of the filter, or if it's original. But based on the pictures of the drain plugs, it looks like mine is part 154685, with the 1/2" NPT threads. The hex head on the sand plug is wider than the threaded end on 154685, which is what mine looks like. So I think I've figured out that part.
The big question is, does anyone think I can replace the sand drain plug without emptying the sand out of the filter first? If I drain the water out of the filter first, I'm hoping that the sand or gravel inside won't instantly collapse and I can get the new plug in. Is this remotely realistic?
If not, I'm going to have to remove the top of the diffuser assembly inside the filter to do anything inside there; there isn't much gap around it. Any hints? Should it just screw right out? Obviously I want to be able to get it apart without breaking anything.
I'm also thinking about wrapping a hose clamp around the hex end of that drain plug and hope it mitigates the leak enough for me to ignore it until swim season ends.