Waterfall Scrubber on a 3 Standpipe Return Set Up

I'm currently running a Waterfall Scrubber on a 3 Standpipe Return Set Up, for those not familiar with it the 3 pipes consist of:

Emergency Standpipe
Full Siphon Standpipe
Open Channel Standpipe

Link to an example: http://www.beananimal.com/projects/s...ow-system.aspx

I have the scrubber connected to the Full Siphon Standpipe. This usually works rather well, sometimes though when the return pump has been switched off then on again for feeding etc the Full Siphon Standpipe can take 5 to 20 mins (depending on when the scrubber was cleaned last) to achieve full siphon again. This is due to air ingression via the scrubber's slot, which prevents the siphon effect happening until the pipe then slowly manages to purge all of the remaining air. It doesn't happen all the time & it's not really a huge or long lived problem when it dose, but it just gets on my nerves a bit listening to the open Channel Standpipe noisily sucking away every couple of mins as it starts & stops siphoning while waiting for the Full Siphon Pipe to kick in again.

So I've been thinking of putting a "U" bend on the end of the Full Siphon Standpipe, just before (& bellow) the Scrubber. My thinking is that the siphon would quickly begin at the "U" bend because the air coming in from the scrubber slot will not be able to go down it & therefore allow the siphon to start? Before I waste my time bodging my plumbing I was just wondering if anyone had already done this or knows of this strategy being employed?

If not what do people think, do you reckon it will work or do I need a re-think? Any ideas?

Cheers :-)

If you are describing a trap, that's a big no. The problem is the horizontal run of pipe (scrubber pipe). Putting a "U" trap will just make it worse. You will not get air to purge out from the tank-side of the trap very easily.

If anything, I would say to drill a hole in the end of the slot pipe to allow the air to purge out from the top inside of the pipe. I'm not sure if this would work but in my head, it seems to be a possible solution. The reason is that I'm thinking that the problem with getting the air out of the slot pipe is due to air getting trapped inside the pipe that cannot escape. Water drains down through the slot but it's not that air can get back up into it, it's that the air pocket inside the pipe is trapped and is preventing the pipe from purging.

So drill a hole on the far end of the slot pipe, in the bottom of the pipe, and push an airline hose into the hole until it touches the top of the inside of the pipe. Depending on your setup, it might have to be drilled through the end cap. But don't drill it in the top or end of the pipe, not sure that would work. The idea is to give air a path to escape. Then take that airline hose to the sump and put it under the water level. So once the air purges out, it should run water through it.

The only problem is that this line may clog if you have flow through it 24/7. So maybe put a little airline valve on it or a pinch-off so that you can stop the water flow once the system starts up and purges - only use it when you manually stop/start. If you have a power outage, you know that the system will be noisy, but it will settle on it's own eventually.

Well the original plan wasn't exactly a trap such as the one you would see on say a sink or a bath. I was basically going to lengthen the return pipe which is just flexible hose so that it would naturally curve down & then back up again before connecting to the scrubber.

But I can see what you are saying about the problem probably being getting the air out rather than air getting in, so I'll give that plan a go next time I get chance. Just wondering though, why do you reckon the hole wouldn't work if it was drilled through the top of the pipe and that it will be better to drill either through the end of the slot or end cap then use an airline to the top?

Glad I asked now before I started mucking about anyway :-)
Cheers.

I don't know, I suppose it would work to drill it from the top as well. I just was thinking that if for some reason the airline tube would get pushed out by water pressure or something, better to have it spraying straight down vs up or sideways.

Yes pointing down would be better than up if something did come loose I suppose. Anyway I'll let you know how I get on once I get round to doing it :-)

Well I finally got round to trying out the air tube through the slot idea the other day when I was cleaning the scrubber. I honestly thought it would be a goer but unfortunately it didn't seem to make any difference so it's got me totally baffled now.lol

I did also try giving the air tubing a careful suck & that seemed to help speed things up a little bit. Obviously I wont be getting down into the sump, doing that & risking a gob full of tank water every time the return is switched off though! As I said it's not really that big of a problem waiting a bit for the siphon to kick in, I'm just a bit OCD on having everything running perfect I reckon.

Drat. It seemed good on paper. Back to the drawing board...