Backyard Aquaponics
A place to discuss aquaponics

The problem is that you won;t be able to flood all the beds and the pump will either switch off, or run dry. Sure enough there will be a time when all the beds are almost full before the siphons kick in.. Well except that they cant be all full, coz there's not enough water.. The volume is not required in the fish tank, it's required in the sump... What happens when all the beds end up 1/2 - 3/4 full, not enough to kick in any siphons, and the sump is empty, and pump is off... The system will be stopped..

I can see what your suggesting, but I'm not sure that it's going to work as you want it too...

Personally I'd look at doubling the size of the sump, at least. Or swapping it to a two pump system and putting a small t piece into the main pump line out of the fish tank pointing back at the fish tank, so when it pumps it shoots water back into the tank as well, when it stops it sucks air so it won't siphon.

I suppose you can always try it and if it doesn't work add another pump in.

Just try to run it for at least a week or two before you get the trout in.

Good points, especially about refitting with a pump in the FT if needed. I do have the second ebara and was thinking there is no reason I could not run both pumps in the sump at the same time - also gives piece of mind in case of a pump failure, considering lack of daily checks over the weekends we probably should be doing this anyway. Should I run both pumps in series to the same 40mm return line or sun a second parallel line?

I am still lost as to the need for the sump to hold all the water, I know this is traditionally the way but I can see no reason you can't use the volume of the tank above the venturi overflow for additional capacity. In this case the feed line to the GB's would constantly be filled and under pressure (I am actually running a 40mm ring main right around the deck to ensure even pressure at every GB) and flow into the bed would be adjusted via a ball valve. I can actually see positives to this such as that the capacity of the system can be much greater than the GB's need and as such the need to monitor evap and top up over the summer holidays would be less frequent.

Joel, I agree about the water in the system cycling for a couple of weeks prior to the fish arriving and plan on doing this, should be ready to fill by Friday - fingers crossed. Concrete pour is tomorrow morning and then it is full steam ahead. This will also allow time for my hypothesis to be proven wrong and rectified , Two pumps in the sump, that is a good idea that we should do now though .

Thanks for all your comment guys, keep them coming. Really would like to know from others what has happened when they have filled their CHIFT to well above venturi drain height.

If I understand what you are attemping it seems that your potential inflow is going to be greater than your venturi outflow. How do you control this while the pump is running? It seems like you will have to be very careful about how much water you are adding to the fish tank versus what is coming out via the venturi or the tank will overflow. I guess the answer would be to put your venturi at a level that is lower than 500 litres (sump capacity) from the top of the tank.

This still leaves the problem where without staggering your grow bed flooding via a rigid mechanical method then you would never have enough water flowing to all 6 growbeds to fill them and kick of the siphons. With a 500 litre sump you could probably do 2 at a time and leave a little for the pump.

Just my two cents worth.

I think you have what I am attempting grasped with 200mm of water over the venturi we would have around 1000 litres for GB filling before it would stop flowing from the FT and without taking any water in the sump into consideration. I think it is achievable, it is just whether two ebaras could cope with the job of keeping the sump empty, I reckon they could but only time will tell I guess.

More measuremenst and fiddling tomorrow and I should have a definite on which way I will go with it.

Any hydraulic engineers/pump experts want to tell me what The maximum flow I will get from two ebaras feeding into one 40mm line over 1.6m head would be

It sounds like you are going to overfill the system. i.e. have the tank filled up 200mm over the venturi and have the sump filled to capacity as well.

Interesting but it still sounds like there is a potential for the pumps to add too much water for the venturi to handle and the tank will overflow or a potential sump overflow if the grow beds all dump at once.

Good luck and keep us posted.

OK I have been running some more numbers and I think I can do it but I need to check my levels in the morning. Based on 40% water in the GB media I would be looking at around 200 litres per GB by six beds so 1200 litres. If I set my highwater mark in the sump at 300 litres that gives me 1500 litres that could possibly be in the tank above the the venturi drain at any time. 1500 litres equates to approximately 300 mm from the top of the tank so if this level is above my GB height I could be on a winner

Assuming I can relate flow to pipe cross sectional area - the 6 beds will siphon to the sump via 20mm outlet - total area of gravity fed flow per bed is 314mm square. Two ebara pumps via two 40mm pipes with area of pumped flow per pump being 1256mm square. Therefore plenty of pipe capacity within the return line from the sump to cope with the 6 beds dumping at once (not likely to happen often). The test will be in seeing if the pumps can cope, if not then we will be having sump overflow and a HSM pending redesign

Can't really be called CHIFT as I reckon the level will fluctuate around 200mm.

More thinking - oh no................ If I was to put a timer switched 40mm reticulation solinoid on the venturi line I could do away with siphons (probably a good idea with little fingers around) and just use trickle drain like Joel uses in his setups, one return pump line from the sump would more than cope with that flow. Anyone know if basic retic controllers will allow for switching every hour?

Can you use a standpipe system (pump in tank, standpipe in growbed, pump in sump) and have an airlock on the growbed side? easiest way I can think of is a larger pipe diameter, see pic:

My advice is keep it simple, get a bigger sump tank. Or connect more containers together to add capacity to your sump. Running pumps dry isn't good for them even if they have safety cut offs to stop the immediate burn out.

Mini sumps are only useful as intermediate drain stages that require extra pumps in the system, ya might as well put on pump in the sump and another in the fish tank and deal with the extra cleaning of the fish tank pump.

Remember that the most precise math on the capacity of plumbing now will be all thrown off once bio-slime gets involved.

Lots of forward movement today and we have decided to go with the FT overfilled, draining via a venturi drain located about 250mm from the top of the tank into the grow beds via a 40mm ring main that drops down to 25mm for each bed. The main off take from the tank will be controlled via a solenoid on a timer - 15 mintes on 45 minutes off or similar, same as a pump but no pump. Beds will drain via 6mm drain holes as per Joels systems (no bell siphons ).

The sump will have two ebaras in it plumbed into a manifold that runs into one 40mm return line, each ebara will have a non return valve in line before the manifold.

Will post some pictures of the days progress shortly.

A single Ebara would fill a 40mm pipe... squeeze two into a manifold, then a 40mm line...

Don't see the point...

Perhaps I've missed sometrhing in your design.

Pics or drawing please... tomorrow...

The two ebaras are not for pumping capacity, without bell siphons dumping rapidly into the sump we have got rid of that problem, the second pump is just insurance.

Being at a school the system will not be attended to over weekends and during some extended periods during holidays so if one pump fails the other one will do the job until it is next inspected. We have tried to design the system with this fact in mind and it has also been considered when we decided on stocking densities. Although this increases the cost and it is not what most would do at home, the design of the system has had to take into account many things that the average BYAP system would not consider.

Anyone know of the easiest way to switch a solenoid from a 24 hour 240 volt mechanical pin timer? Standard retic timers do not have enough start points each day for what we need. Any other suggestions for getting a solenoid to switch for 15 or 30 minutes in the hour would be appreciated.

Thanks for all the comments guys, you are keeping me on my toes and making sure I consider all possibilities.

Cheers,
Mike

The b store have 2 timers hpm for 10 bucks that can switch every 15 min if you like i have been useing one of these for 2 1/2 years no problem

I have been looking at the 240 volt HPM mechanical pin timers that will switch in 15 minute intervals but need to find something that I can plug into it that I can wire up to a solenoid. Don't know yet whether it will be as simple as using something like an old phone charger or similar plugged in and wired directly to the solenoid? I need to find out more about solenoid input voltage and amps.

Still having trouble visualising things... earlier post suggested two ebaras, each with a 40mm pipe...

Have you changed this to be both pumps having a 40mm take-off pumping to a common manifold?

And earlier you said you intended to return to the sump from the growbeds via 20mm pipe???

Even allowing for the rare occurance of six beds draining at once... even three beds might have difficulty....

I'm wondering if all six beds will drain in the 45 min off time... even if staggered...

Need a diagram to get my head around it.... I'm not good at visualizing such things...

There was talk about each pump having a separate return line when I was considering using bell siphons that would dump the beds quickly. We are now planning on using Joels drain method which is the standpipe with two holes in the base that drain the GB during the no inflow time - 15 minutes on 45 minutes off seems to be the standard that works for draining the BYAP GB's using this method. I mentioned 20mm outflow from the GB as that is the diameter of the reducer that is used in the standpipe construction, this actually feeds into 40mm pipe but all water from the GB's must first pass through the 20mm aperture.

In essence we are using Joel's typical system setup but trying to do it using a venturi drain as the feed from the FT that is regulated (timed) using a low pressure solenoid valve. It is increasingly looking (as I do further research) like this won't be viable due to the cost of the low pressure solenoid valves and the possibility that 40mm pipe won't provide enough flow pressure to the GB's. If this ends up being the case then a Tornado or similar pump in the FT will be run off a timer. We were just hoping to be able to not run a pump in the FT as no pump would mean one less thing that can fail over weekends and holidays when no-one is around.

The current plan for two pumps in the sump is purely safeguarding against sump overflow if one pump should fail over a weekend.

Thanks all,
Mike