Hello! Ive just got my new system up and running and your seeing my plumping in the middle of a rework. Before I cut to many pipes and give myself a bigger headache I thought I'd ask the community to help verify what might be going on and ensure I am solving the problem in the right way.
The system can be seen here: http://imgur.com/a/kU75t
Where I am currently at: I Have a sump tank with a single pump in it pumping upwards. This splits in 3 places - about 25% up to a return back into the sump tank, about 75% up it connects over to the plumping that feeds the grow bed. Then at the top it dumps into the fish tank. The fish tank drains from a gravity drain back directly to the sump, keeping the water level in the fish tank constant. The 3 grow beds are all flood/drain systems setup with a bell siphon, all working correctly.
My issue: Over time the water coming out at the top of the pipe, into the fish tank loses power and eventually stops. This means no water making it to the fish and is obviously a bad thing. If I stop/Start the pump, plenty of water making it to the fish, good power, etc. I assume this is because I have bleeds located below this point and over time gravity wins and takes all the flow into this pipes instead.
My idea to fix: I am guessing that I need to run all piping to the maximum high (top of fish tank) then T from there and have it feed down to the grow beds and seperately into the fish tank, that way 100% of the water makes it to the maximum height and is then just forked to its ultimate path.
Anything else that can cause this? Im assuming this is due to the waterlevel fluctuating in the lower sump tank so the head heigh is variable. When the sump is very low (when the top tanks are all about to drain) the pump has to work harder to push another foot or two upwards which results in lower flow to the top? Any way to work around this? Am I misunderstanding the problem?
BTW, even a gravel guard that is too restrictive will also cause problems as will to few holes at the bell bottom. Note that my bells are about 50% open at the bottom.
In doing my own research it seems my problem with the drains not triggering is due to a lack of backpressure. This is a result of me going from 1" to 1.5" on the way down from the standpipe and then draining through a horizontal pipe thats larger (the 1.5"). This prevents enough back pressure and is why I need both beds to drain at the same time. In doing some research online it seems one way to add back pressure is to place the final return point under water in the sump, this creates the required back pressure and works from my testing - I do think there is 1 problem and it might relate to the air gap you mention above. I think what I observe is that if one bed fills first and starts to drain, it creates such a strong siphon that it will "early drain" the other bed before its high enough to actually trigger its own siphon.
Could you explain what you mean by air gap? Are you referring to a T joint with the T part facing up to allow passing air out?
I've attached a picture of my sump with the return line underwater so you can see what Im referring to.
I think in the end I'll have to run totally seperate lines like you suggest. I was trying to make things look a little nicer with a single combined pipe but its turning out to bite me :)
Thanks for all the help!
Blake, any air gap will do. I use a T in the common drain (I have 5 IBC 12" media beds all running into a common drain running below the beds) and I run a 1" pipe over and up the back of the beds at each bell drain entrance but others just run the 1" into an open T of a larger size and get the vent that way. Most people do not understand house plumbing and the fact that EVERY sink, toilet, tub, shower, etc. have a vent in the wall that breaks the siphon of the drain lines. In the case of house plumbing all those vents go out the roof. Just look at the roof of any house. It is called the "stink pipe" and without it all the traps in the house would interfere with each other and empty every time a sink was used or a toilet was flushed and then all the septic gases would be in the house. Plumbing 101. You must separate the drains from one another and all it takes is a vent to do that. I vented every 2 beds as you can see in the picture but I should have done each one. Working fine for 4 years nonetheless.
Thanks for the reply, you have been tremendously helpful in the design and buildout of this system and I greatly appreciate your advice and tips. I'll see about adding an air vent like you suggest, that does make alot of sense now that you've explained it. Things have been running smooth for 24 hours now, which is the best its done in a year :). I think a couple gold fish will be soon.
Next up I think I need to get a solids filter going. I have plumbing to support one just need to get a barrel and create one.
Just to update things here --
I decided rather than figuring out how to get two drains draining at the same time to plumb them separately . This instantly fixed my problems and things are working perfectly. I've added a light screen over my sump tank and fish tank to keep debris out as there is a large oak tree above/nearby that likes to share leaves. I've added 12 goldfish as of late yesterday. This morning I awoke to two that had died - Im going to attribute this to either shock or water temp - its a bit warm. Will monitor and see if I conitnue to have fish problems.
Thanks again for all the help. I'll try to figure out a solids filter in the coming weeks.