Using a Slow Pump in a Well, by Tunnel Rabbit

This is a follow-up to my recent  SurvivalBlog article: My Solar-Powered Dankoff Slow Pump System. (See: Part 1 and Part 2.)

In the SurvivalBlog comments section, Homer asked for some details on using a Slow Pump in a Well, and he gets it.  It is good to know just how versatile the Dankoff Slow Pump is.

From the Dankoff literature: It is possible to use the Slow Pump should the well casing be at least 6 inches in diameter.   The filter and foot valve in this situation, should be the Dankoff model, a 30 inch in length filter and foot valve companion, that is attached at the end of the 20 foot inlet pipe.

This is the 30 inch filter and foot valve:


https://www.altestore.com/store/solar-water-pumps/pump-accessories/foot-valves-filters-strainers/30-filter-and-foot-valve-assembly-plus-spare-30-filter-p360/

My Recommendations

I would prime the inlet pipe, or make an accommodation to prime the pump inlet from top side with a flexible line that runs to the top, before lowering the assembly into the well.  The pump is lowered to within 10 to 15 feet, or closer as you may dare, to the static water level.  Within 10 feet, the suction side will prime itself, but the static level may change over time, and we have a built-in a method to deal with that possible change.  Raise or low the pump in the well as needed. The pump is not water proof. If it become wet and blows it’s 7 amp (24 volt), or 15amp (12 volt) ATC fuse, pull it out and dry it out.

Because the pump does its pumping slowly, it may not affect your well’s static level much, and likely not at all.

What model pump should be use?

The depth of the static water level is the bottom measure to include with increase in elevation, and where the water must be delivered.  It’s not easy to figure the actual TDH (Total Dynamic Head), so just figure the total elevation the water will be lifted, and choose the pump with next highest. and maximum elevation number on the Dankoff chart.  This insures that we’ll have a pump installed that will have enough extra capacity to make up for lack of a way to determine the actual TDH, or pressure limit.

The Dankoff Slow Pump chart:

in feet:
http://www.dankoffsolarpumps.com/pdfs/Dankoff_SlowPump.pdf

in meters:
http://www.maskamwater.com/wp-content/uploads/2018/08/Dankoff-Slowpump.pdf

If the well is 250 feet deep, and the static level is, say, 200 feet, and the point at which the water will be pumped to is 100 feet above the well casing, then we need a pump that can easily handle a height of 300 feet.
According to the chart, the 1304-24 can pump to 320 feet, but it is near it’s limit, and there is no margin for error.  The distance, or total length of the pipe in not included in the calculation, and friction in the pipe is accumulated with distance and pipe size.  So the let’s be safe and choose the next pump model lower in number, and with the higher elevation number on the chart.  That would be in this case,  the 1308-24 (400’@ 1gpm)  — (The Model 1308-12 is the one that I happen to have).

Looking at the chart, we find the PV requirement is 250 watts to lift water 400 feet with that pump.  And add 40%, if no pump controller is used = 350 watts. I’d get a bit extra, 400 watts or more. If the water is only lifted to 300 feet, the chart says the #1308 will produce at a maximum, 1.1 gpm.  If the pump is powered by the solar system that runs off batteries, reduce that number by 20%, because of the lower voltages in regulated power.

If the house is run on 12 volts DC, then the pump to get would be the #1308-12, the one I have. (is it a coincidence, no).  If supplied with 12 volts,#1308-24 (24 volt) would only produce half that of the #1308-24 rating (1.1 gpm), or about .5 gpm.  Why? If the 1308-24 is fed 12 volts, it produces half it’s rating, because half of 24 is 12.  Yet the 24 volt motor will not be harmed.  It can be used.

Because the pump is now at least 200 hundred feet below the surface we must choose the size, or gauge of wire to deliver full voltage and amperage.  So we use a voltage drop calculator on line.  

https://www.calculator.net/voltage-drop-calculator.html

We’ll need to push 8 amps with 36 volts for a nominal 24 volt pump, when run directly off the panels.  The calculator says we’ll have a 5% loss (acceptable limit) in voltage if we use 200 feet of 12awg wire.  We can use less expensive 12 awg wire. If we use the 1308-12, a 12 volt pump like mine, we need to use the harder to find, and more expensive 8 awg, or the easier to find 6 awg.  Yet the calculator show that 10 awg has  only a 6% voltage loss instead of 5%.  Close enough for the slow pump. We can also use 10awg.  If the panels are not at the well head, then we need to run the calculator again with the actual length, from the static well level to the sunniest nearby location.

If the photovoltaic panels are located far from the pump head, then the 24 volt model is probably the most practical choice.  If the distance is greater than 800 feet total, then the 48 volt pump is best. Of course the 48 volt pump can be used regardless.  Should the panels be damaged by a CME, or EMP, to supply it with alternative power via a generator, or a vehicle alternator, or regulated tread mill motor, would not be possible unless a voltage converter was used to step up from a 12 volt system to at least 24, 36, or 48 volts.  In an emergency, two 12 volt batteries could be connected in series to create 24 volts that would run the 48 volt pump at half speed.  Of course we could also find four 12 volt batteries to run it at full speed.  It is a bit cumbersome, but it could be done.

And because we are pumping using the #1308, the pressures it can create when lifting water to the maximum 400 feet, the pressure in the line could reach 175 psi.  Note that 175 psi would burst the inexpensive poly pipe rated to only 70 psi, so we need to use a High Density Polyethylene Pipe. This is a manufacturer’s part number, DR11, that handles 200 psi.:

http://www.jmeagle.com/sites/default/files/HDPESpecSheet4710%20.pdf

Or you can just go down the local pumping outfit and pick it up.  To connect this stuff, all you need is a propane touch to soften it up a bit, and hose clamps,and hack saw to cut it.

Addendum:

Some helpful references and manuals in PDF files and other formats, for the Dankoff Slow Pump:
.
http://www.dankoffsolarpumps.com/

http://dankoffsolarpumps.com/pdfs/Intro_to_SWP.pdf

http://www.dankoffsolarpumps.com/pdfs/slowpump_booster_instructs.pdf
https://www.humboldtsolarwaterpump.com/layout-diagram-for-dankoff-solar-slowpump/




2 Comments

    1. Ideally, it is better to use a submersible pump designed for that job, however, it is good to know the options, and to have the ability to adapt. Of course it can be use in shallow and hand dug wells, and those instances with any filtering system available. PVC pipe could easily handle those pressures as well, but it does not handle a freeze, and must be protected. Also, the example applies to pumping longer distances, and to heights the #1308 is capable of, 400 feet. Using larger diameter pipe would help ensure the maximum gpm is delivered, as there is friction. Because the gpm is so low, and the rotor vane type pump will build pressure until it reaches it limit, going up just one size, 3/4″ is likely enough if attempting 400′. And note, do not use a valve on the output line to control the flow. The pump will build pressure until it either bursts the line, or breaks the pump.

      Just got call to go fix the cooling system on a propane fired generator. Hope I have the tools for that. In that vane, I would also make sure to have the tools and spare fittings, extra adapters, and tools to reconfigure, to fix and adapt equipment to changing requirements. Be able to use what ever plumbing might be available, such as garden hose, pvc, poly pipe, 1 inch galvanized well line, and even copper. It can be cobbled together in a pinch. Think like a farmer during the Great Depression.

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