I was searching online for this recently, expecting that everybody must be building these things... only to find almost nothing of the sort. My guess is, it's something that all kinds of people would be using, if there was a design out there that actually did the job. So, with some trial and error, I managed to come up with one of my own that works pretty well.
First, the disclaimer: It's not perfect. It requires really good water pressure (but not a huge volume of water), usually won't self-prime, and isn't good at sucking up rocks. It will also drain a pond fast, but I think any pond vac will do that. Priming it is fairly easy -- put the vac line in the pond and cover the exhaust pipe with your hand until it fills with water -- so I'm not too worried about that detail.
As for the positives.. it sucks like a monster, and it chews through mud / leaves / etc. with little effort. It's small, needs no maintenance, and setup / cleanup is quick. Any clogs that might happen, happen right where the hose connects, and just pulling the vac pipe in and out of the pond a couple times (shaking it axially) creates a water-hammer effect that clears anything other than rocks or big sticks. Whatever makes it past the inlet, easily gets through the rest (especially after the jet of water shreds it). I used it to suck out mud, old leaves, bunches of leaves with twigs (from a recent storm), and a big horrible mat of string algae. The pond went from looking neglected, to being able to see the liner again, pretty quick.
I'm not sure if you can tell how to build one just from the pics, but I think it's pretty straight forward. I may post a real drawing / bill of materials in the near future, if that would help. The second pic shows how I made the nozzle, which is the only part that's not off-the-shelf; the basic idea is to take a bit of 3/8" OD copper pipe, and squeeze the end smaller. I did it by drilling a cone-shaped hole into a block of aluminum with a countersink, and then hammering the tubing into it. The only other weird feature is where the two elbows connect at the bottom.. one is 1.25", and the other is 1.5". There's no pipe between -- we want (I think) the pipe to be expanding from here on out. So, the two faces of the elbows are glued together directly.
It does generate fairly good pressure at the outlet (it's a close relative of the jet pump, after all), so you can probably connect a dump hose there. My pond has a storm drain next to it, so I haven't had to try. If you do, it should probably be a big one (2 inches or so), as any back pressure will subtract from your vacuum. Dumping onto the ground would probably make a huge mess...
The design is really sensitive to the exact proportions of the parts. The tip of the nozzle, its exact angle / spray pattern, and the length of the pipe it sprays into, definitely have big effects on its performance. For all I know, mine might work half as well as it could, with one or two small changes! This is why I haven't bothered (yet) to post exact measurements of anything. You will probably want to mock it up first (I used lots of duct tape), and experiment a bit before gluing everything together. It's entirely possible that you'll come up with one that works better than mine.. please post if you do!
[edit] -- I should probably have mentioned, the tip of the nozzle is about flush with the very top of that grey hose connector. It's not extending into the chamber at all.
First, the disclaimer: It's not perfect. It requires really good water pressure (but not a huge volume of water), usually won't self-prime, and isn't good at sucking up rocks. It will also drain a pond fast, but I think any pond vac will do that. Priming it is fairly easy -- put the vac line in the pond and cover the exhaust pipe with your hand until it fills with water -- so I'm not too worried about that detail.
As for the positives.. it sucks like a monster, and it chews through mud / leaves / etc. with little effort. It's small, needs no maintenance, and setup / cleanup is quick. Any clogs that might happen, happen right where the hose connects, and just pulling the vac pipe in and out of the pond a couple times (shaking it axially) creates a water-hammer effect that clears anything other than rocks or big sticks. Whatever makes it past the inlet, easily gets through the rest (especially after the jet of water shreds it). I used it to suck out mud, old leaves, bunches of leaves with twigs (from a recent storm), and a big horrible mat of string algae. The pond went from looking neglected, to being able to see the liner again, pretty quick.
I'm not sure if you can tell how to build one just from the pics, but I think it's pretty straight forward. I may post a real drawing / bill of materials in the near future, if that would help. The second pic shows how I made the nozzle, which is the only part that's not off-the-shelf; the basic idea is to take a bit of 3/8" OD copper pipe, and squeeze the end smaller. I did it by drilling a cone-shaped hole into a block of aluminum with a countersink, and then hammering the tubing into it. The only other weird feature is where the two elbows connect at the bottom.. one is 1.25", and the other is 1.5". There's no pipe between -- we want (I think) the pipe to be expanding from here on out. So, the two faces of the elbows are glued together directly.
It does generate fairly good pressure at the outlet (it's a close relative of the jet pump, after all), so you can probably connect a dump hose there. My pond has a storm drain next to it, so I haven't had to try. If you do, it should probably be a big one (2 inches or so), as any back pressure will subtract from your vacuum. Dumping onto the ground would probably make a huge mess...
The design is really sensitive to the exact proportions of the parts. The tip of the nozzle, its exact angle / spray pattern, and the length of the pipe it sprays into, definitely have big effects on its performance. For all I know, mine might work half as well as it could, with one or two small changes! This is why I haven't bothered (yet) to post exact measurements of anything. You will probably want to mock it up first (I used lots of duct tape), and experiment a bit before gluing everything together. It's entirely possible that you'll come up with one that works better than mine.. please post if you do!
[edit] -- I should probably have mentioned, the tip of the nozzle is about flush with the very top of that grey hose connector. It's not extending into the chamber at all.
