Pumping into and out of tw different sized water tanks piped in series

[turbzero]

Hi

We're constructing a water treatment plant. At the start of the system we're pumping (discharging) via a positive displacement pump into a receiving 10,000 litre round tank (approx 2.1m high x 2.5m diameter). This first tank is connected to a second larger 22,500 litre water tank via a 1.5 metre long 20mm NB pipe at the bottom. The second tank is approx 2.1m high x 3.7m diam. Thence, we're pumping out of this second larger tank (with a centrifugal) and discharging away. The inflow capacity will vary from 25 to 40litres/second and the outflow will match this. Tanks are on the same level.

My question: As the pump pumps from the second tank, will the (gravity fed) 200NB connecting pipe allow enough water to flow from the smaller first tank into the second tank, without the smaller tank overflowing, particulary at the higher end of the envisaged flow rate?

 

[bimr]

Don't know exactly what you are doing, so this addresses just the pipe flow.

The 200 mm pipe would probably work, but you would be better served with a larger pipe of 375 mm. The cost difference for the pipes will be minimal.

The 200 mm pipe will result in a higher velocity which may cause some issues in your process. There will be a velocity jet as the water enters the tank. The 200 mm will cause a slight hydraulic gradient from tank to tank.

 

[turbzero]

Thanks bimr.

The idea of the two tanks is to remove energy and air from the water being delivered by the positive displacement pump (from a ground and surface de-watering area). We did originally want a baffle of some sort in just one tank, but we decided on the second tank to take the initial discharge and the second tank would be a much calmer state for air to escape and maybe also some suspended solids settling. I agree, I think it is better to just bite the bullet and go larger pipes between the tanks.