Pool circulation

[Hardbie]

Hi guys,
I'm looking for some input. We are building a scuba training tank using a 7'6" high and 18' diameter corrugated steel water storage tank with liner. I'm planning on using a sand filter system. The tank comes with two take offs which I am planning on using for the drain and return. I am thinking that the drain take off would be about 12 to 18" off the bottom and then the return take off would be a few inches under the water line. Pump will be turned off during use to avoid water movement and potential issues with suction. The tank is going to be indoors. Is there any need for a skimmer or will these two take offs be enough for filtration? I am planning on finding a way to hook up a vacuum hose and brush to the drain so any debris can be sucked up from time to time.

Does any of this make sense? Will this work? Is there anything I need to consider or look out for?

Cheers
Rich

[Denniswiseman]

Hi Rich and welcome
I wouldn't leave the main drain that high as it won't remove any debris in the tank bottom and could injure people. I suspect that this a potable water storage tank and the lower one is designed to not suck out any debris from the tank bottom
A skimmer would be advisable to remove any floating debris (flies, spiders and dust) albiet you won't have any leaf or pollen problem
You could also add another suction line to prevent any one being trapped
There is also the need to check what regulations apply to the type of installation you are proposing as it would be a commercial tank

[Teapot]

Main drains don't do very much anyway unless you push the dirt into them with a brush, that said up the wall as you envisage it will do even less.
As Dennis said a skimmer is a good idea as dirt enters from the top.

I would skim from the top and return through the bottom, that way you won't have any suction issues. dirt on the bottom will get lifted towards the skimmer. Plumb the bottom inlet via a 3 port valve and you can switch it to a drain when required.
Sorry I work in metric but the tank will hold about 50m3 and a 6 hour turnover means you can filter at 8.3m3/hour using v little electricity through a 24" filter. Backwashing at 16-18m3/hour so a variable speed pump would be a good idea or a speed controller for a single speed pump.
What do you think?

[Hardbie]

Thanks for your responses.

Yes this is essentially a potable water storage tank. So to prevent us from having to fabricate plates for an 'in-ground' skimmer unit would we be able to use a floating one (as seen on some above ground pools) and then either have the hose go through the wall of the tank or even over it to the pump and filter and then return through the lower hole in the tank.

Now, thinking about and writing the above. Do I even need holes in the wall of the tank. Could I use PVC pipe and run it down the inside of the tank thus preventing any potential leaks.

Metric is fine for me.

Cheers
Rich

[Teapot]

Hi Rich,
Why would you need to fabricate plates for a wall skimmer, you may need to locally make that part of the tank flatter but all the parts should come with the kit as it would for a standard panel pool. Yes you could use a floating skimmer and bring the pipes up and out but don't rule out the KISS principle! I built a system similar to the description you gave for a customer a couple of years back but their's had to look nice. That works well but when their liner needs changing we will fit a through the wall skimmer.