Mentioning this for poops and lolzs, but the gas powered water pump from harbor freight pumps a reasonably small amount of water at low RPM. It could provide a low flow with some pressure.
i used one to set up a prototype "mixer" of sorts on ag equipment. It worked amazingly well at low rpm.
also you can throttle it up and it goes full friggin firehose. Folks in the wooded windy areas like Wyoming use them with a fire nozzle, ready to drain a swimming pool of other reservoir in case of fire.
edit:this one is smaller than the one i used. This may work even easier?
Something like this.
Home Depot: 94520 1/2 HP Convertible Jet Tank System with 24L Tank
Home Depot: Standard Whole House Water Filtration System Two of these, the first with a 5 micron sediment fiber filter and the second with a 5 micron carbon filter.
Back when we lived like Little House on the Prairie at our primitive lake cabin, I buried a 1500 gal. tank in an insulated railroad tie box and filled it with lake water that I treated with 1/3 to 1/2 cup of Clorox bleach. More in the summer and less in the winter. I can't find the ppm ratio offhand but when I was figuring it out, I called the local health district department and their official told me the correct answer. We never used it for cooking or drinking. Just the right amount and you could barely smell it, too much and you could feel it on your skin and it would bleach your hair. Not enough and it would stink from the water heater. I had it tested for bacterial coliforms just to make sure in the beginning.
It was fun walking out onto the ice and drilling a hole with the ice auger and dropping down a submersible pump in -10F weather. The 1" poly pipe would never freeze up as long as I was pumping, but the second I turned off the pump, the entire line would freeze up since at the end of the hour it took to fill, it was only pumping through a 3/8" hole in the otherwise frozen line. I would have to drag the 100's of feet of hose and coil it inside the cabin until it thawed and then drag it back outside to drain and be ready 2 weeks later to do all over again. Family of 5 with laundry.
Nowadays, I have a 300 gallon pickup tank and drive 12 mile both ways and haul rural water from the towns rural water system. Bulk water cost $4 per 300 gallons. Plus we don't live there year round anymore.
So I worked in a pump factory for 10 years. Project management and a little bit of engineering. Big suckers for power plants and refineries.
I think this is a fairly simple application. For water, pressure is .4435 psi per foot. So, for a 20' lift and no need for pressure at the top, you need a pump that can generate 20 x .4435 = 8.9 psi at the pump outlet (which is near the bottom of your tank), at your desired flow rate. That's pretty low. You'll select a slightly higher pressure than that to account for losses and "other stuff". You'll set the pump at the bottom of your tank (I'd use a submersible pump for this application) and measure to the highest point that the water needs to flow, do the math above, that look for a pump with that pressure rating at your desired flow rate. I know I wrote some of that twice.
Let's talk about submergence. With the pump placed at the bottom of the tank, you will need a minimum height of water covering the impeller, to provide enough pressure at the impeller to prime the pump and avoid cavitation. Pump manufacturers / sellers should provide this submergence value in their technical data. If you go with a simple sump pump, which will probably be fine, it should have a float switch that will keep it from running if the water level is too low. Submergence is related to Net Positive Suction Head (NPSH), which is more complicated. Just mentioning that in case you run across the term as you learn about what you need. Just focus on submergence.
If I was sizing a pump for a industrial application, the most important things I'd want to know are flow rate and pressure. Then I'd select a pump that operates at your desired values while running in the middle of its flow/pressure range (I'm simplifying). For your simple application, provide those two values, and maybe an electrical constraint like voltage, and the pump seller should provide suitable options. They'll tell you power requirements, discharge pipe size, submergence required, and maybe pressure at zero flow ("dead head") so that you can select a pressure rating for your discharge pipe.
The above was general and basic and off the top of my head after not having thought about it for 12 years. Feel free to ask specific questions. I'll remember more if you give me specific questions, and I can go look stuff up.
Thanks guys. I think this will be easier than I thought. 10 gpm would mean two 2.5 gpm showers and someone filling stuff in the kitchen at the same time with room to spare.
wake74
Reader
1/9/23 9:42 p.m.
I haven't done these calculations since passing my PE exam many (many) years ago, but David's explanation is excellent above. Just remember that 10 GPM rating is kind of useless without knowing what pressure that is at, back to Davids comment about a pump curve. A cheap 10 GPM pump that pumps 10 GPM with an open outlet is a different pump than one that will pump 10 GPM up 20', through a 50' of 1" pipe with fittings, valves, etc.
While the staff of Piping and Process Engineers on my current team would be insulted by this, you can use an online calculator, to estimate your pressure drop. Something like this: https://www.freecalc.com/fricfram.htm
Here is another one that will let you add in vertical head pressure to get your total head: https://www.pumpfundamentals.com/php_pages/pump/head-1.php
You can pump as high as you want so long as you are pushing water and not pulling. Deep well submersibles use multistage impellers to add vertical. But even a cheap well pump will do a lot of height.
