I agree it should have a cover on it, just hoping that it is threaded onto the pvc piping and not glued. I can place my palm over it with the system running and the suction is strong initially but in a second or two the suction releases - I think it is tee'd into the skimmer line. My goal is to be able to use it for vacuuming the floor and of course cover when not in use.
Whew! If the suction releases like that, then it sounds like it might be half way to being compliant. Still needs the cover, though. It sounds a lot like an equalizer port. Here's an interesting article:
Equalizer Lines & Anti Entrapment | Automated Aquatics
There are some pictures at the bottom you might find helpful. With any luck, maybe what's on the end of your port accepts a VGB cover without modification, and the cover is just missing. You'd just need to figure out what brand it is, and find the replacement cover (if it still exists). Do you have any way of taking a good picture of it? Which you could post here? And/or distribute it to online pool stores, to see if anyone recognizes it and can recommend the correct cover.
If it is an equalizer port, I wouldn't know if that could be used as a vacuum port or not, even if you could get a fitting for it to accept a hose. If you cover it with a spring-loaded flap, to make it both compliant and able to be used as a vacuum port, then you'd have to turn off its suction before the flap engages (each time after you vacuum). It's likely you'd have to manipulate the skimmer's float valve each time to do that, both before and after you vacuum, and if that's so, it might be just as easy, or easier, to connect your vacuum hose to the skimmer port and leave the equalizer port covered properly. Additionally, if you convert it to a vacuum port in that way, with the flap cover, you lose the benefit of an equalizer port. And if it is part of a dual (T'd) port, then a flap cover will in effect close off one half of the dual port, making the other half dangerous! Any of that making sense?
Again, this is all supposition on my part, about what the port actually is, how it might be plumbed, and how it could be used for vacuuming. Just brainstorming with you...
I just wanted to point out its potential danger. And the subsequent danger(s) that you might be introduced by modifying it. I had a pressure port that was converted to a vacuum port. While it was (is) compliant for the most part, there is a condition that now exists that could make it non-compliant, and dangerous (though a few things would have to go wrong for that to happen). That didn't exist before I had the port modified. Neither the "professional" that did the work, nor I, were aware of this problem before the work was done (and we
both should have been). I only happened to discover it by reading here at TFP! Point is, be careful with modifying pool plumbing without fully understanding its implications!
