I ended up buying the hub and unfortunately it was tapped 1/2" NPT at the lateral positions. I had already bought new laterals that were 3/4" NPT - they were a steal on eBay , 8 for $30. I drilled out the hub and tapped the 8 locations with 3/4" NPT. All is good, and you can see top and bottom pictures of the completed lateral assembly below. (By the way that reflection in the water is something rarely seen in Seattle!)
I have another question someone might be able to shed some light so here's a little background first.
My sand filter is very old, it looks to be an early model Sandpiper and has a nice solid stainless steel housing which seems like it would last forever with periodic maintenance/updates. Online parts drawings for 24" Sandpipers show a style with a necked down top housing section. Mine has a full diameter top section but in all other respects it appears identical to online parts diagrams.
The hub/lateral assembly is bolted to the bottom of the housing where it sits over the return port feeding out the bottom and back to my Multiport (also an antique). On the inside, coming up from the hub is a little tube which goes through a hole in the top spray head. This appears to be an internal air bleed line that I'm guessing is intended to vent air trapped inside the hub, so it can make its way to the top of the housing. I'm thinking it makes an easy path for air to bypass the sand layer which would prevent any "explosive" decompression events from disturbing the sand or possibly damaging the laterals. It may have had a miniature check valve on the end of the tube at one time but that's disappeared long ago and the filter seems to work fine without whatever kind of valve it was. (The tube is item #10 in the parts diagram below and although it's actually one piece with the hub. I think it's shown separately so you could buy a replacement if you broke it off accidentally)
So my question is, in my new lateral assembly, should I duplicate this internal vent line - if that's what it is - or is it unnecessary and can be ignored - and am I guessing right as to its purpose?
Thanks!
