Set up a siphon with a vacuum pump for my seaweed cultivation tank?

Hi guys, I'm setting up a seaweed farm right now where we're cultivating seaweed in rectangular concrete tanks. The tanks are 1000L each, rectangular with concrete walls at an elevation, about 40' above sea level, and the goal is to drain the seawater to the ocean. Since the tanks are concrete and simply drilling an outlet in the bottom will create issues, I am thinking of setting up a siphon to remove the water to a 200L drum at about 20' elevation that can then fill up and drain to the ocean so we have some control over the exchange.

We want to set up an automatic primer for the siphon since the exchanges aren't continuous but occur 3x/day. I was thinking of using a T junction at the highest point of the siphon, with the inlet entering the 'T' and the vacuum pump hooked up to the 'handle' of the T. Would this work? I'm new to this kind of work so would appreciate all help. Thank you!

Welcome to PF.

seaweedfarmr said:

I was thinking of using a T junction at the highest point of the siphon, with the inlet entering the 'T' and the vacuum pump hooked up to the 'handle' of the T. Would this work?

Yes, it can work if you arrange it correctly.

You will need to keep both ends of the siphon underwater at the start of the transfer. For a short lift siphon, a vacuum is not needed, only a depression is required. A suction pump would only need to lower the pressure by about 10 kPa, or 1.5 psi, to get the siphon running. I would make a small reservoir tank chamber the top of the 'T', with a float valve to turn off the suction pump when the siphon was primed.

You could stop the siphon with a valve, but allowing air to enter the top tank would also stop the siphon. That could happen automatically at the end of the drain cycle when the tank is empty. Opening a valve at the top, or running the priming pump backwards for a short time, might achieve the same thing.

An outlet drain bowl will keep air from entering the siphon during priming. How much water will you remove from the growth tank? The surface in the tank needs to remain above the drain bowl surface at the siphon outlet.

@BillTre

The siphon approach could work but it could also fail as I have seen several do in the past. Of course yours might be better designed.

To me the most straightforward way to do it would be to supply the new water to the system when desired (using a timer controlled valve or pump and have it overflow in a controlled manner. For me that would be through a hole drilled through the side of an aquarium, with a bulkhead fitting installed to fit piping taking the water to a drain.
Drilling glass or cement is not that hard with the right equipment. However, you may have other problems with this approach that are not described here.

There are other ways to do siphons.
@Baluncore was right about putting an outlet drain bowl downstream of the siphon for priming. It would also be possible to use the siphon just to get the water flow out of the main tank and use a timer controlled valve to control water flow out of the downstream valve. Unless you drain too much water and break the siphon (get air into it) the siphon should keep working.

Philosophically I don't like using siphons too much in this way. They are easy to disrupt and fiddly.
These systems can go wrong in many ways. You should examine what could go wrong and the consequences of those wrong goings:
Tank drains completely

• the level in the tank the water could drain down to can be determined by the level the tank outlet is at or the level at which you siphon breaks.

Water goes in the wrong place (floor)
Pump problems
There are mechanical ways to prevent these problems if you think about them ahead of time.