This article is in response to a question that I received from another blog reader, that was forwarded to me by the SurvivalBlog staff.
Reader O.S. had written, to ask:
“I would like to ask a question regarding your Aug 4th, Survival Blog article in the water section. You mentioned an “inexpensive Shurflo model number 9325″. I would like to confirm that the model number is exactly the one you are noting. The reason is, the best price I can find online is $895 at this location:
Other dealers have even higher prices. When you noted “inexpensive”, it led me to believe that perhaps the model number is incorrect? Would you mind confirming the model number is correct?”
The photovoltaic-powered water pump that I recommend for large gardens was indeed the Shuflo Model # 9325. It is the model that replaced the original and time-tested Shurflo 9300. That is its pedigree. I had used the term “inexpensive” in the context of the cost of other deep-well water pumps that are considered to be proven. There are less expensive Chinese clones, but I cannot recommend them for deep well applications. Be sure to perform the usual due diligence before purchasing it and understand its design limitations. At a minimum, I would also purchase several rebuilt kits to support the Shurflo 9325 for a decade of operation.
If you have a large garden this would work to irrigate a garden. However, a Dankoff Flowlight pump could be used to charge your current system, or a Dankoff Slow pump could be used for irrigation and for delivery of water to livestock or the house and garden at a distance and where a deep well is much lower in elevation to the destination, and any pump can be used as on-demand pump if it is operated remotely by an electric switch. The Shurflo 9325 could also be used to pump water from surface water sources such as a lake or creek. The Dankoff is a better pump for the purpose, but the price of the Shurflo 9325 at around $850 is hard to beat. That is less than half of the price of the Dankoff Slow pumps that require filtration. The Dankoff Slow pump will however have a service life that is 3 to 4 times longer.
While I will use the Dankoff Slow Pump as an example, the principles and performance of this pump can be applied to other brands of solar-powered pumps as they work similarly. I am using the Dankoff pump as the exemplar as I know that a chart necessary for reference and comparative purposes in this PDF.
As an example, if 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 pump the water to a greater height then a booster pump of some kind could be used. This booster pump could be another type of pump that is best suited to the task, or it could be another Shurflo 9325 pump. As I am not a hydrologist, it can be a bit tricky to estimate the Total Dynamic Head that includes the friction created by the line and the increase in elevation, so it is best to just estimate the head (pressure) or increase in elevation, and use a pump that comfortably exceeds the performance level determined by an estimate.
This rough method of over-engineering may also have another benefit as the pump may produce closer to its full rated potential, and the pump motor will also last longer as well. According chart provided by the new owner of Dankoff Pumps, the Dankoff Slow Pump model #1304-24 can pump to 320 feet, but it is near its design limit, and there is no margin for error. As the height (head or pressure) increases, its ability to pump decreases and it delivers less water per minute or hour. The horizontal distance, or total length of the pipe in not included in the calculation, and friction in the pipe accumulates with distance and varies by pipe size. It is not necessary to figure out the TDH (Total Dynamic Head). So let’s be safe and make it easy by choosing the next size up or the pump model with a greater capacity to pump. That would be in this example, the Dankoff 1308-24, with a maximum 400’ lift @ 1gpm).
Sticking with this example, and looking at the chart, we find the PV requirement is 250 watts to lift water 400 feet with the 1308-24 pump. By adding 40% to increase the size or output of the PV array to compensate for the lack of a pump controller that converts voltage into current during low light conditions, more water might be produced in low light conditions. Because PV power is now inexpensive, I’d get a bit extra for good measure. That is, more than the recommended maximum of 400 watts and evan a bit more if you’d like. Adding an extra panel or two also provides much-welcomed insurance should one or more of the panels in the array become damaged, or fails. At the least, the pump would then produce more in low light conditions and more water in clear sky conditions and throughout the solar day.
If the water is only lifted to 300 feet, the chart says the #1308 will produce at a maximum rated output of 1.1 gpm. If the pump is powered by the solar system that runs off batteries, then reduce the rated output by 20%, because of the lower voltages provided by storage batteries or regulated power. Pump controllers use a Linear Current Booster that utilizes MTTP technology that will produce more voltage and or in low light conditions additional more current and less voltage in low light conditions that are present in morning and evening hours and during periods of cloud cover. Water production is steadier, or less likely to be interrupted during periods of cloud cover if a pump controller is used.
If the house is run on 12 volts DC, then the pump to get would be the #1308-12. If supplied with 12 volts, the #1308-24 (a 24-volt pump) 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 of its rating, because half of 24 is 12. Yet the 24-volt motor will not be harmed. It can be used. This reduction of output is directly correlated with the voltage if the current remains proportionally high enough. To make sure the wire can deliver the increase in current needed use the gauge of the wire that supplies the power is that adequately large enough in diameter. Use an online voltage drop calculator to determine the gauge of wire needed to provide twice as much current or a proportionally greater current given a lower voltage delivered to a pump rated at a higher voltage. Here If it is difficult for you to use, search for another and simpler calculator.
By installing a heavier gauge wire to supply power to a Surflo 9325 that is a 24vdc rated pump, we can use a 12vdc power without reducing the output more than half, thereby getting the most out of the pump when using a lower voltage. This kind of built-in flexibility is engineering in redundancy and that is a good thing as “redundant redundancy is redundant” and that is what we might need in unforeseen and extreme circumstances of an austere setting where there will be no resupply or ability to fix stuff right, and where water is our most important resource.
Remember: No water, no life. Get additional and separate water pumping capability and redundant spare parts supplies, and engineer in redundancy where possible. Pretend that you are headed to Mars and can never return. If you can step up to the more expensive solar power-operated hand pumps then you’ll have a built-in redundant capability for a deep well.
The Shurflo #9325 is the lowest hanging fruit, but it is not necessarily the best choice if you can afford a Grundfoss that works very well to produce lots of water from wells at great depths and with A.C. and D.C power supplies. Look up video demonstrations by Engineer775 on YouTube. I’m not an engineer. I just barely made it out of high school, and the U.S. Army said I was only qualified to be a dishwasher. Of course, I did not buy their B.S. and did not join. But Engineer775 is a civil engineer and has extensive experience with the best systems money can buy. Study up, since this is an important decision. Put more money into water production than you think you can afford.