Backyard Aquaponics
A place to discuss aquaponics

Yeah, dont you hate it when there is one more page in the thread

Your shroud needs to be at least 1 inch higher than the top of the drain pipe to start the siphon properly. Dont know why, it just is.
If the bed still overflows, just cut down the inner pipe some more.

An angle grinder works well for cutting pvc.

How high above the top of the bell cover was it rising before in the test setup?
Is water flowing out of the U-bend?

The U-bend depth may be too much for the siphon to kick in before it overflows the GB, this can be adjusted by decreasing the length of the inner pipe and the shroud pipe...if the GB has a larger volume to the test setup, then the water is going to rise slower and take a little longer to kick in

a) decrease the U-Bend air trap height, if this is easier to do - make sure that it still traps air tho

b) decrease the height of inner/shroud pipes

Fixed it by lowering the height of the drain pipe - thanks for your help

Ok, so I finally connected all 4 GBs today to the drainage system. I'm yet to get them filling at equal rates, but with a bit of tweaking I'll sort that out. After tinkering with overflow heights to get them to correct levels, i'm now having an issue with how the siphons are kicking in.

Note that all drains are 20mm coming out of the GBs, into 1 x 20mm drain pipe back to the FT (basically 4 x 20mm into 1 x 20mm drain). As the GBs fill, only 1 will start siphoning, and eventually another will kick in. Meanwhile, the other 2 seem to be trickling out the overflow at the same rate as they're filling. Only 2 will ever siphon at the same time. As one finishes draining, another starts.

I assume this is due to the main drain pipe being the same diameter as the GB drains. I'm thinking if I have each 20mm GB drain empty into a 50mm or 100mm main drain, they should all start siphoning as soon as they're respective overflow is reached. Is this correct?

Yep

Been there tried that.

The siphons need to drain into open space, iff the pipe is already full from the other bed siphoning - the next beds will not start.

I would use 90mm DWV (the green stuff) as a drain. It can handle 8 x 19mm siphons all at once...just.

Thanks mate - glad I least understood what the problem was. Fluid dynamics was never something I've bothered with before!

I'll change the drain pipe tomorrow, and hopefully have it all sorted so I can get going on the GB media. Not looking foward to wheelbarrowing it from the front yard to the back though

Also, could I get away with 4 x 20mm siphons into 1 x 50mm drain, or should I go to 1 x 90mm or 2 x 50mm drains?

Depends on the angle of the drain pipe. If you can set it up to be pretty steep, the 1 x 50mm will do probably, but if the angle is not available either 2 x 50mm or 1 x 90mm would be good.

Probably one advantage of running 2 x 50mm is more aeration upon return to the tank. Two x splashes instead of one.

I've now connected each GB to it's own 20mm drain pipe. I thought about merging them into 2 x 50mm or 1 x 90mm, but it was actually cheaper getting 3 x 20mm pipe than it was 1 x 90mm!

This has the added benefit of being able to monitor by site which GB is draining.

However, I still have some issues. I'm struggling to get the siphons tweaked to my liking. Currently, they seem to be draining once they hit the overflow, at almost the same speed as they're being irrigated. After a couple of minutes of this dribbling out, they eventually start to siphon properly. Is this due to the irrigation flow rate being to low? Is it even a problem? I thought/hoped that pretty quickly after hitting the overflow they would have started siphoning.

This causes a problem with different GBs taking different amounts of time to drain once they reach the overflow. Whilst I can eventually tweak the fill rate to be about the same, different drainage rates will make it difficult to set my timer. I was hoping for the last GB to start siphoninh before the first one had finished. Perfectly, it would be good to have all beds fully drained when the pump turns off, before they start filling again (or am I being pedantic?)

FWIW, I've noticed that the heights (in mm) of my drain pipes (20mm) and siphon pipes(50mm) are slightly different, as follows:

• 1: 205 - 222
• 2: 195 - 222
• 3: 201 - 220
• 4: 199 - 222

Hopefully Les the siphon master can review them to see if they're good

In theory, if they're all identical heights, with identical flow rates, should they fill and drain at the same time?

Hi Ryan
No matter how hard you try the syphons wont act in harmony, they will gradually swing out of sync. Its quite normal for the syphon to trickle for a while before it kicks in fully.

You have a choice of auto syphons and no timer, or a timer plus standpipes with a hole drilled near the bottom to drain the water out during the pumps "off" cycle.
If you use auto syphons with a timer you run the risk of leaving the beds flooded during the pumps off cycle due to the sync issue.

I see. This explains my headaches trying to get them to all be in sync.

Using the autosiphons takes about 10-15 minutes to fill, and 5 minutes to drain. Is this cycle suitable for continuous pumping?

On the other hand, if I go to with the drilled standpipes, I assume they will take a fair bit longer to both fill and drain. Would this require a larger pump?

Timings sound about right Ryan... and yep ... just run it continuously...

Yeah, don't even bother trying to sync them - too many variables

Size of media will be different hence less/more water required
roots will take up more/less space in each GB
Pumps maybe rated the same, but could be out by a couple of litres (that is if you are using more than one pump)
depth of water in the U-bend if it differs by about 1mm could mean a few more litres added to the GB to kick in the siphon
...and the list goes on

You saw my dual bell siphon connection - one GB fills in over 5 minutes, the other GB does it in 4 1/2 mins

thanks guys.

Whilst I've finally got my siphons working fine (as much learning/experimenting as anything), I'm still tossing up whether I should keep them, or use the drainhole in the standpipe method.

I need to suss out the pros and cons of each. The drainhole method would allow me to put the pump on a timer, and proably save a bit of electricity. Also, it would ensure the GBs could never overlflow, which they almost have a couple of times with the siphons.

On the other hand, I'd need to use quite a small drainhole due the slow irrigation rate, and I'm concerned a smalll drain might get blocked.

Anyone care to comment on the pros and cons of drain holes in standpipes vs siphons?

You could use fair sized holes if the pump can fill the bed in under 15 mins and has excess capacity. The drain holes can be sized to take any excess pump capacity.
For example, a 30,000 Lph pump would put 7,500L into a 1000L bed in 15 mins, allowing you to use pretty big holes in the standpipe. I doubt anyone would use this sort of ratio but you never know