Hi, I found a thread from 2007 where a fellow had inherited two pressure tanks in series, and was trying to understand what was going on. In my situation, I have no pressure tank and a pump that has been replaced twice in 12 months under warranty. Clearly, time for a pressure tank. One website recommends that the volume of the pressure tank should be equivalent to 1 minutes pumping, to avoid too much start/stop which is apparently the killer for a pump. So maybe two tanks in series were used to provide this capacity. I would appreciate your advice on calculating required pressure tank capacity. Pump is an 800litre/hour submersable Bianco, providing rainwater to a suburban house/garden. Thanks, Edwin

I was with you until the last sentence. Is this pump just for watering a garden, or are you using it for your house water?

If for house, then you would want a pressure tank. I'm amazed it didn't have one. I can only imagine someone hooked up a booster pump which can be used without a tank but is not made to do what you are using one for. At any rate, you can get a tank too small, but it would be hard to get one too large. The larger the tank, the longer the cycles for your pump. This 30 gallon tank http://www.freshwatersystems.com/p-303-wellmate-wm-9-well-pressure-tank-30-gal.aspx?affiliateid=10052&utm_source=shopzilla&utm_medium=Feed&utm_campaign=Product&utm_term=WM-9 has a 9 gallon drawdown, meaning you can pull 9 gallons before the pump has to cut back on again. Personally, I'd go for one a little larger. I wouldn't put them in series. We've had people come on this site with problems doing that. When you are troubleshooting, it's just one more thing to have to consider. I'd rather have one fifty than two thirties.

Thanks for that jlisenbe. Sorry to have been confusing. The 2500 gallon rainwater tank provides water to both house and garden, through an automatic switching device which provides town water as soon as the tank runs dry. http://www.biancorainsaver.com.au/. (havnt figured out how to actually make a link, sorry).The pump is submerged inside the tank. I bought the system new, and a pressure tank wasn't suggested at the time. From what you are saying, I should go for the largest pressure tank I can afford, but there is no general rule-of-thumb for how big one should be?

I don't know of one (rule of thumb). I'm not familiar with that system, but the concept seems straightforward enough. I use, if I remember right, a 40 gallon pressure tank and it is plenty large.

Are we talking about a galvanized pressure tank or a blue bladder tank? Back to you, Tom

I think he would have to use a bladder tank, based on his description of his system above.

I think he would have to use a bladder tank, I keep reading "pressure tank"/ Big difference. You recommended a 30 gallon what? Pressure or bladder? Are you looking to store water or maintain pressure? Cheers. Tom

He's talking about pumping water from some sort of rain storage tank. Since this is not a well, I would think that would rule out the old galvanized tank system.

I actually mentioned a 40 gallon tank.

I'm still not clear how this type of system is supposed to work the way he has it configured now. The pump would have to cutin on demand and cutout when demand stops. That just seems strange. I can see that for watering the lawn, but not for use in a house. So I would think a pressure tank would be not just helpful, but really essential for this person. And as I said above, I don't think a galvanized tank would be practical for him.