Will a pressure tank function well with direct water flow into it. Pump->1000 gal. Cistern->Pressure Tank-- water leaves Cistern at 28lb. Pressure into pressure tank for upper floors. Cistern has float in it for pump to turn on after 18 inch draw down. Pressure tank will trigger nothing.

How is the cistern generating pressure... elevation?

I don't think you will be wildly happy with 28# pressure, but to answer your question, the pressure tank doesn't care how water gets to it under pressure. If you stick water under 28# of pressure in it, it will put out water at 28#. However, I would think that most systems such as you are describing would employ two pumps: pump>cistern>pump>checkvalve>pressure tank.

How is the cistern generating pressure...elevation?

I don't think you will be wildly happy with 28# pressure, but to answer your question, the pressure tank doesn't care how water gets to it under pressure. If you stick water under 28# of pressure in it, it will put out water at 28#. However, I would think that most systems such as you are describing would employ two pumps: pump>cistern>pump>checkvalve>pressure tank.

Elevation. In line pump of some sort? I'm off grid so any use of electricity is a concern. Another pump is what I figured also, thanks.

It must be elevation. You would need about 70' of elevation to produce the 28# of pressure. If you don't plan on using a second pump, there is no reason to have the pressure tank. Pressure tanks cannot generate pressure. The elevation of the cistern will do that. So the pressure tank would serve no purpose.

Centrifugal Pump? Will this work with pressure flow into it, instead of it pumping up flow. Positive Displacement Pump? Either way, I still have downward pressure of water into unit, instead of up, to have water pressured up into house. Doesn't sound right.

A booster pump is designed to take water under pressure and increase the pressure. If you have 28# out of the cistern, and you say it is due to the elevation of the tank (which, again, would have to be 70' or so), then a pressure tank would do no good at all. It would be 28# in, and 28# out.

Take a look at this. Water Pressure Booster Tankless Well Jet Pump 3/4 HP on eBay! (http://compare.ebay.com/like/290354367569?ltyp=AllFixedPriceItemTypes)

Let me add one more thought. I'm not sure what you mean about downward or upward pressure. Pressure is pressure. 28# of pressure will move water up or down. It moves down more efficiently, but it still moves. I'm just saying that a pressure tank, of itself, will not increase your pressure.