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Awesome. Thanks for the fast reply too

So I either apply a valve in the Bottom drain where it levels out above the ST or adjust the height to get the desired effect.

you mentioned that the bottom drain can go higher than the overflow I see how that would then effect output but is it true that I can not go higher than the water level in the FT?
I also drew my overflow incorrectly as it needs to go below ground then up to allow easier access. From my understanding of your water properties that wont matter

At least I can now add filter to the bottom drain return only using the extra height

Thanks again Your effort in these forums is priceless.... I couldn't count how many mistakes I would have made not haing read the type of information posted in here

Cheers

(In very general terms) Gravity won't "allow" you to lift water higher than where it started!

Are you moving water and waste from the FT to a sump?

Another simple way to reduce flow in the bottom drain is simply use a long length of pipe and/or a narrower pipe.

Cheers Bunson

I am filtering the bottom drain only before returning to the ST.

I have about 400 mm to play with between the water level and the top of the sump.
I will play with the length of the bottom drain pipe to get the less than 20% return through that.

I believe I also need to add an anti siphon like a T piece in that as a precaution

Thanks to you both..

As you have drawn it the bottom drain is lower than the side drain. Raising the bottom drain outlet above the side drain outlet will reduce the flow through the bottom outlet relative to the side drain. Lift it up until it is level with the FT water level will really reduce the flow because it will stop

Actually looking at how water levels change as you change the height of two drain outlets from the same tank can really illustrate why making small changes in an AP system can suddenly cause things to stop working reliably particularly in the case of siphons.

If you raise one drain outlet you reduce the fall through that drain.

This reduces gravity's ability to draw water through the pipe.

This means that the water is not as free to leave the tank.

This means that it takes more head (higher water level) to push the water through the drains.

This means that more water will start flowing through the other drain but as the volume of water going through the other drain increases the velocity increases hence the friction losses increase which means that more head is required to push the water through the drain.

However, as the water level in the tank increase the static head at which the pump has to work increase which reduce the flow.

I could go on but you get the idea. Every time you make a change it causes a bunch of other changes and these are not apparent straight away the opposing forces take a while to reach equilibrium so another thing to remember is that when you make a change go away and have a coffee before you make another.

The engineering calculations in this and other threads I've done are to get you in the ball park and then you make adjustments until its good enough. Then...

DONT CHANGE A THING

Note I said "good enough" not just right. I can't cound the times I've said to myself...


In your case once you lift or lower the bottom drain it will take time for the water level in the tank to stop changing. If you raise the drain the flow will decrease. If you measure it straight away it will be less than if you measure it half an hour later. So make a change go and have a coffee.

Note I said coffee although tea would be fine. I cant count the times I've substituted beer instead and ....DOH!

Should have just gone strait to the rum...

This thread started out great with water flow. I even had to lookup a couple words (spargers being one). LOL

Though I'm not in the same size category as many of you, this thread made me realize that my 378 liter tank has NO proper water flow. The input line simply points at the bottom of the tank and is only 20 cm off the bottom. I'll see if I can add in a T and a 90 degree to create a make-shift spargers. I'm not sure how my venturi bubbles will act, but it'll be fun no mater what.

Thanks for making us new AP guys think differently. I never thought I'd be reading papers from different universities on water flow and nitrification processes, to mention just a few.

I would put a true union ball valve on the bottom drain pipe before it joins the other pipe or goes to separate filtration areas. You can open it and flush the bottom line every week or two and eliminate major drain cleanings.

Also works great for harvesting b/c you can actually drain the tank (put in a T where the valve is )

Thanks Ryan

That is another great idea Between the FT and ST have a T which would support a vertical pipe with valve to use as a flush and could be used to drain ....

I think I understand you fully

I lost sleep last night pondering configuration of all this (im sure I am not the first lol)
Would it be better to have the upright closest to the ST on this bottom drain pipe go from the 50mm (underground) to 25mm (vertical feeding the ST). I am assuming the flow will be faster therefore more likely to purge debris from the pipe?



Cheers

What size to use depends on your flow but yes the smaller the pipe the faster the flow but consequently the more pressure/friction losses so you need a greater fall. If you get the pipe size right you shouldn't have any settlement in your drain but having said that having a drain point below the FT is handy for flushing and draining the tank should/when it proves necessary.

I did another thread on drain sizing here:

viewtopic.php?f=14&t=21129&hilit=xtutex

which you may or may not find useful.

Hi Stuart.

mmm!

I have read your threads on Pumps and Drains awhile ago. I still have fear running through my veins.
I keep thinking 'what have I gotten myself into'
My math IV brain fried looking at the vowels and consonants in the calculations

If you lived in Perth I seriously would have you over in a heart beat (Paid) to tute me, I am a visual person so my venture from here on is try and see what happens but before making decisions read read read these threads. This way I may glean something simple to implement which overcomes potential issue later


I have taken a number of pieces of advice from you which include

Pump should be one of the last things considered
Bottom drains assist with self cleaning (had one installed in the tank I purchased)
All pump efficiency questions can be answered with a NO! Which tells me not to stress atm.

I will definitely be back when it comes to the pump purchase later. That really screws with my head....
My only guide for making that decision is something I made up
- tank size plus grow bed volume per hr + 10% for pipe velocity fittings (all the stuff you speak of)

Dont any one take that as gospel, its just my ostrich in the sand approach to dealing with that aspect of AP

My try and test approach may kill me yet.
Its still early days in my project

You could always pop into Cheidys (the shop formerly known as BYAP) in Jandakot... lots of good advice available there.

It took me a while to get my head around the concepts too.


That is a valid way of going about things. As would be learning how to do the calculations as would copying someone else's design as is getting someone to design it for you. Horses for courses.

The only negative thing I would say about the test and try approach is the increased environmental footprint from the waste (fittings and such). Plus some things are hard to change later. My BYAP system is a good example of that and the problems I had with it 5 years ago are what drove me to understand the engineering thoroughly.

Hey Stu, what's the name of your thread, would love to go thru it!


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