color me stupid somebody want to edumacate me?

[OzSolar]

Pond or fountain pump? They operate with 1' of water or less.



captive air tanks are used there for a bit of water supply, and in hot water loops to allow expansion.

When your (circulator?) pump moved water, you didn't want a vacuum drawn without pressure to move water in from behind.

This wouldn't work for an un-pressurized open system. But with a closed system not fed by municipal or off-grid pressurized system, you should be able to attach one of these tanks, fill with water/purge air. Then pressurize the tank. That would maintain a moderate pressure as you circulated, and as temperature changed.

Kinda sorta but there's a lot more going on than that, but whatever, it's all good. The OP and I have been talking about an atmospheric system the entire time. See below.

Plan is too run a non pressurized system with two grundfos circulation pumps to move water into the two fan radiators that I got (cheap).

 

[time2roll]

Yeah no plans to pressurize tank.

plan was for 2" pipe from tank to the circulating pumps they each have a 3/4" input, I guess I will have to play with it and see. worse case I replace pump with a positive displacement pump, but they use a lot more power to operate I would bet.
@Hedges thanks for the input. Thanks to all actually, helped clear up some questions I had.

Is this a closed system? If closed consider an expansion tank. Water can expand significantly from chilly to hot and create significant pressure. Easy to adjust the pressure of the expansion tank.

 

[Daddy Tanuki]

Is this a closed system? If closed consider an expansion tank. Water can expand significantly from chilly to hot and create significant pressure. Easy to adjust the pressure of the expansion tank.

no, its an open system due to the tank design. converting it to pressurized would not be cost effective.

 

[time2roll]

Seems like a big enough system that the pump will have no cavitation issues if installed near the low point.
Bottom of a 1700 liter tank has to have plenty of feed pressure into the pump. Not moving water that fast either.

 

[OzSolar]

thanks, i will keep that in mind... thats more power out from the batteries at night, not a deal killer depending upon how much the pump I find uses.

Actually the positive displacement pump uses less wattage that my other Grundfos circulators but they are antiques, as in from the early 80's, that I also salvaged from a solar hot water project I got paid to dismantle.

 

[Daddy Tanuki]

Actually the positive displacement pump uses less wattage that my other Grundfos circulators but they are antiques, as in from the early 80's, that I also salvaged from a solar hot water project I got paid to dismantle.

got a model number? i went to that website and 5 million options... and I am lazy. If you got something that works hook a brother up with the data!

 

[time2roll]

I was using an older version of this Grundfos series: Very low power draw.

https://product-selection.grundfos.com/us/products/alpha-north-america?tab=products

I plan to install similar for my current house on the fresh water system (not space heating)