OK, so I've been PMing Dave to try and understand why he thinks diagram #2 would also drain a pond. To me this kind of thing is important because many people come here as guests looking for answers and to me plumbing a pond correctly so a pond can't drain is about as important as it gets.
Apparently when Dave said diagram #2 would also drain the pond he was imagining something that wasn't in the diagram. I was having a hard time understand this in the PMs, one because it wasn't in the diagram and two because it would be such a bad design it never occurred to me.
Apparently he thinks there should be a valve on the vent pipe. I think this has been called an "air valve", "relief valve" maybe. An owner could close the valve to do something I don't totally understand. So the pond could be drained or "purge" the bottom drain. Well yes, if a person did that it would indeed be bad. Diagram #2 is specifically to stop that, which is why
diagram #2 won't drain the pond.
The other things, "being able to drain a pond" and "pruging the BD" are sparate issues. Just like the diagram didn't show a pump doesn't mean a pump isn't needed, it just means it isn't in the diagram. But yes pump placement is important, but it a complete blueprint of an entire system to show a single feature only serves to make a single point into a totally confusing mess.
So in addition to venting a pipe and running it so the pond won't drain should the vortex (or any filter) dump valve be left open we can add more features to the discussion.
Valve to drain pond
This is how to properly add the valve to drain the pond. The valve should be label, painted a different color, run to a location, pad locked, etc. You don't want 2 identical valves on 2 identical pipes right next to each other. Should you ever be away and someone else has to take care of your pond you want to make everything they have to as clear as possible.
Draining a pond is a very, very rare event. Replacing the liner, and I can't think of another reason. Because of that I would never, ever put the above drain valve on a pond. Lots of people new to ponds really, really want such a valve because to them they have lots of fantasies about how a pond works. It's difficult for them to believe a pond wouldn't need to be drained.
The reason I wouldn't add an emptying valve is two fold. First,
it would drain the pond. Anyone reading this thread is hopefully somewhat aware of the issue of plumbing a pond that would allow this to happen. Second, I'm cheap and lazy. The emptying valve serves no useful purpose. Should the pond ever actually need to be drained I would just set a pump into the pond and empty it. Anyone keeping a pond at this level will/should have an extra pump at all times so it isn't an extra cost.
Purging the bottom drain.
I'm not sure I understand what Dave meant by this, but I assume it has to do with clearing a clog in the bottom drain.
I suppose you could plug the air vent and open the vortex and yes that could drain the pond should you walk away and go watch TV. Why a person would do this is strange and so yes if the clog were to suddenly clear that person will be screwed. There are lots of ways people can override any safety feature if they choose.
Aside from overriding a safety feature this stunt also isn't very effective. For a couple of reasons. First capping or closing the vent pipe does nothing. You have a clog right? That means there' no water in the horizontal drain pipe where the vent is located. When you close the "air valve" nothing is going to happen because there is air still in there. The clog isn't going to allow for enough water to enter and replace the air. Now, yes, there are all kinds of Rube Goldberg solutions to that, but we're really starting to go past the insane sign post at some point.
The second reason this wouldn't be effective is just the nature of clogs. When a BD clogs it's being pushed away from the pond. Trying to add more force to push it even harder may clear it.That's just like your bathroom sink. When clogged you can fill the sink to the top with water and hope the extra force will open the clog. I can't yes that would never work but have you ever seen that work. More often it won't.
The most effective way to clear a BD is to push it in the opposite direction. Shoving a garden hose down the vent pipe and snaking it thru the drain pipe (we used sweeps instead of 90's right?) it very effective. There are a couple of gizmos made to go onto a garden hose to create a very powerful jet just for the purpose of cleaning clogs. After that we break out the drain snake, same device used to the world over to clear household clogs. Works great.
So that's why diagram #2 is effective in
not draining your pond and why the design shouldn't be "fixed".
This has been exhausting. It always seems to be exhausting to try and explain the simplest of pond building techniques in any forum these days. Back 20 years ago it was more fun, no one knew anything about pond because the backyard pond concept was new. There were tons of things to discuss, new ideas everyday. In any one forum there might be 5 ongoing threads about new filters like vortex, TT, settlement. I remember when I was designing the Muck Mop in a forum there were like 3 other people designing their own vacuums. We could discuss and discuss what changes we made that day, discuss improvement and even disagree. It was very exciting and creative.
I miss those days. When I post today I fantasize I'm back there. Maybe that's just getting old. I always hope to find that again but I think the web has changed. Back then there weren't any advertisements, forums were mainly for just for sharing ideas. Today it's all about getting as many eyeballs as possible. Getting as many eyeballs as possible and serious discussion seem to be at cross purposes.
