Pressure tanks in series: different capacities

[Roam]

Hey all,
I have a fairly large system on which I am looking to install multiple pressure tanks (air bladder type). There are currently two 80L tanks hooked up and I am looking at adding a 300L as a third.

Question: if I install pressure tanks of different capacities in series on the same system, will I be able to use all the volume available? Or will my draw down be limited to the smaller 80L, essentially leaving 220L in the large tank unused? Will the pressure switch trigger prior to using the full capacity available in the 300L tank?

Thanks in advance for all the advice

 

[Reach4]

Pressure tanks are not an efficient way to store water to carry you thru occasional water pressure loss. It can work, but the storage capacity is only about 25% of the nominal size. It does have a significant advantage over a big atmospheric tank in that no extra pump etc is needed.

If you do this, have a check valve feeding the tanks.

But in answer to your question, yes, adding more tanks will add more capacity. I would set the air precharge in each tank to about 24 psi lower than the normal water pressure. Semantically you could say the tanks are in parallel, or you could say in series. No big deal. We know what you mean, whatever word you use. The tanks don't have separate input and output pipes.

My choice of 24 was fairly arbitrary. Lower would stretch the diaphragms more, but would add more capacity. 30 psi below the normal water pressure might be OK, but it would worry me that I was maybe shortening the tank life.

Note that I said diaphragms rather than bladders. Diaphragm pressure tanks are normally more durable than pressure tanks with bladders.