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Llamafish's Auto Siphon Woes
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Author:  Llamafish [ Mar 7th, '07, 09:38 ]
Post subject:  Llamafish's Auto Siphon Woes
Hello Everyone!

I've been lurking for a month or two while slowly gathering materials and am just starting on my first test aquaponics system. My design is basically a grow bed positioned above a fish tank running a flood and drain system using a little pond pump and an auto-siphon.

The first task I'm working on is just getting the auto-siphon working in the garage. After reading over the many threads on siphons, I decided to go with something like dthawk (and Les, I think)'s design of a pipe within a pipe.

To my amazement, my first trial run with everything just hand tightened worked! ... most of the time ...

The problem that I'm having is that sometimes when the siphon is first starting, or when it should be stopping, it instead flows slowly and keeps the water level constant. If I pick up the outer pipe a little to provide more flow, the siphon will kick on (if its starting) and stay strong, even when I put the outer pipe back down, or it'll suck air and stop (if it should be stopping).

I tried widening the crenelations on my outer pipe, but unfortunately I still get this problem intermittently. The outer pipe is presently 1 1/4" PVC, and the standpipe is 1/2" PVC. While the ratio between the standpipe and the outer pipe seems good, the male fitting that I have going into the bottom of the grow bed is significantly wider than the stand pipe.

Am I correct in thinking this is a flow issue inside the siphon?

Should I just make the crenalations taller? (I hesitate to do this because I think it will make the water level in drain mode be even higher).

Or should I just bite the bullet and go out buy a 10 ft length of 1 1/2" or 2" PVC and make a new outer pipe?

Attachments:
File comment: This is the outer pipe that goes over the standpipe, after I modified the crenelations to make them bigger.
outerpipe.jpg
outerpipe.jpg [ 12.52 KiB | Viewed 4643 times ]
File comment: This is the stand pipe inside the grow bed.
standpipe.jpg
standpipe.jpg [ 7.43 KiB | Viewed 4647 times ]
File comment: Black tub on rickety card table over aquarium...this is my siphon testbed =)
siphon_setup.jpg
siphon_setup.jpg [ 27.56 KiB | Viewed 4642 times ]
Author:  GotFish? [ Mar 7th, '07, 09:47 ]
Post subject: 
You have no crenelations in the stand pipe? Oh and welcome to the insanity that is syphons.
Author:  jtjf_1 [ Mar 7th, '07, 10:19 ]
Post subject: 
Drill a hole in the top of the outer pipe for 1/4" or smaller clear tubbing like you woud use on an air pump. Then Run the tubing from the hole on top to the bottom near the level you want the siphon to stop. Thats what i had to do to get it to work.
Author:  Dave Donley [ Mar 7th, '07, 10:27 ]
Post subject: 
Welcome Llamafish!

My guess is that the outer pipe is too wide. Anyone else have what diameters are working for them? Also, how close is the cap on the outer pipe to the top of the inner pipe?
Author:  Dave Donley [ Mar 7th, '07, 10:40 ]
Post subject: 
Hi LF:
I just checked my old autosiphon bucket in the garage (it's cold out there!) - the pipes I had used were 3/4" and 1 1/4"
Author:  Nova [ Mar 7th, '07, 10:45 ]
Post subject: 
Try and have as little air gap inside the outer pipe, between the top of the inner pipe and the top of the outer pipe, as possible. Seems to start easier this way. Maybe also try a smaller diameter outer pipe (1" maybe). If the bottom won't fit over the tank fitting, use a 1 1/2" to 1" reducing fitting.

May help you out, I use the looped syphons as my beds are small and I can get away with less flow.

[edit] What DD said. :) [/edit]

Nova
Author:  dthawk [ Mar 7th, '07, 10:51 ]
Post subject: 
Welcome!

The difference between the outside and the inside pipes should be equal to the diameter of the inside pipe. For example, if you have a 1/2 inch inside pipe, your outside pipe should be 1". The clearance at the top should be 1/2" and I would make the crenelations at least 1" with that big fitting you have. Below the tank your discharge should be at least half as deep as you growbed. It looks like yours is. I hope this all helps.
Author:  EllKayBee [ Mar 7th, '07, 16:57 ]
Post subject: 
hi LF and welcome to the forum.

A few points:
the outer pipe needs to be at least 50% greater than the inner pipe, so the pipe sizes used shouldn't be a problem ( bigger than 50% is not a real issue).

The crenellations need to be a minimum cross sectional area of the stand pipe so water will flow freely (these also seem to be big enough)

The cross sectional area between the top of the stand pipe and the bottom of outer pipe needs to be as big as the area of the standpipe so water can flow easily.

An air tube is needed so that the siphon seal is broken properly and air is sucked into the pipes (jt pointed this out)

....and then there is the pump flow - is it high enough.

If you are unsure of any of what has been said - list the points and I will calculate/explain them for you.

There is a lot written here Auto siphons

This might help also........one inch = 25.4mm

have fun :twisted:
Author:  veggie boy [ Mar 7th, '07, 20:23 ]
Post subject: 
If it helps at all - my bell siphon is 25mm pressure pipe inside 50mm pressure pipe. The height of the outside pipe is 27cm. This is a couple of centimeters longer than the inner pipe. The crenelations are not high - only 1cm - but are very wide (I will take a picture and post). The air pipe is about 7 or 8 mm vinyl pipe I think. I will also take a picture of the positionning of this. As Les has pointed out - the water flow is key to these siphons. Too much inflow into the bed and the siphon will not stop. Too little inflow into the bed and the siphon will not start. The good thing is that anything inbetween will work and this range is large. What you might find though is that when close to the highest inflow that will allow the siphon to stop - the siphon will suck air for a considerable time before it stops - but it will stop all the same. What happens is that when the siphon sucks some air - the outflow will slow - however gradually the level will get lower and lower until enough air is being sucked through the breather hose and the crenelations to stop the siphon. If you start with the flow at the top end of what works - then this is not a bad thing because as the flow reduces with build up of biofilm in the pump pipe - the siphon will continue to work - but will probably stop more quickly than whent he flow was greater. I don't know if any of this makes sense to those that have not already used these siphons.
Author:  PleaseTeachMe [ Mar 7th, '07, 20:29 ]
Post subject: 
Thanks for this info - it hase helped ME at least :)
Author:  monya [ Mar 7th, '07, 20:31 ]
Post subject: 
the pics you have described will really help.
Author:  veggie boy [ Mar 7th, '07, 20:50 ]
Post subject: 
Here they are then - these are just of the outer part of the siphon setup.

Attachments:
File comment: Outer siphon pipe.
DSCF3732 (Medium).JPG
DSCF3732 (Medium).JPG [ 41.26 KiB | Viewed 4567 times ]
File comment: Crenelations.
DSCF3735 (Medium).JPG
DSCF3735 (Medium).JPG [ 42.86 KiB | Viewed 4559 times ]
Author:  Jaymie [ Mar 7th, '07, 20:56 ]
Post subject: 
very neatly done, those crenelations :)
Author:  veggie boy [ Mar 7th, '07, 20:58 ]
Post subject: 
Borrowed Les' chainsaw ;-)
Author:  GotFish? [ Mar 7th, '07, 20:59 ]
Post subject: 
Them wern't done with no wood chisel!
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