Answering Your Water Pump Questions
with RPS Engineer Mike
What are the factors to consider when sizing a pump?
Sizing a submersible pump for your well can sometimes seem like a daunting task as you may not be aware of the different factors to consider when doing research on a pump to purchase. Depending on the situation, some factors may be more important to consider when sizing your well pump, so it is always recommended that you talk to a specialist if you are unsure about what pump is the best fit for your well. But if you are unable to do so, hopefully this article can help clear up what factors are worthy of consideration.
The first big factor is the well depth. This is the biggest factor that will help determine the pump that is the best fit for your well. Usually a deeper well will call for a pump with a higher horsepower so that it will have the power to pump the water up and out of the well. There isn't a hard line rule that wells of certain depths will use certain horsepower pumps, but a deeper well will often use a larger HP pump.
Similarly to the well’s depth, the depth of the well’s static water level is also a very big factor to consider. The static water level of the well is how far down the well you have to go until you first hit water. This is where you start measuring the lift from, not from where the pump is placed. A good way to think about why the lift measurement starts there is to imagine yourself in a pool carrying someone underwater, they aren’t really heavy until you break the level of the water, then you can feel the weight. It’s the same with the pump, it doesn’t have to start fighting against gravity until it pushes that water beyond the static water level. So this is possibly the most important factor to consider after the depth of the well, as it will tell you how much lift you have to overcome in order to pump out of the well.
Speaking of lift, if you are pumping the water into a pressure tank, you will need to factor that into the total lift measurement. That is because you need to be sure your pump will be able to push against the back pressure of a pressure tank on top of pumping out of your well. The way to calculate this is that every 1 PSI = 2.31’ of lift. So a 60 PSI pressure tank will add the equivalent of 138.6’ of lift onto a pump. You need to make sure you factor this into your total lift, if you don’t then it could mean the difference between a pump that works and one that won’t.
The last big factor worth mentioning is the refresh rate of your well, or how many gallons per minute your well is capable of producing. This is important because you want to try and get a pump that will not pump faster than your wells refresh rate. If you pump at a higher rate than your well can produce, you will end up pumping the level of the water down, and if you pump for too long at that rate you will bring the water level down to the level of the pump. You could end up running your pump dry, which is very bad for it and can cause it to overheat, permanently damaging your pump. Sometimes pumping faster than your refresh rate is unavoidable, such as in a situation where your well is only producing 1 GPM. In that case I would highly recommend that you get some sort of low-water protection for your pump so that when the water level reaches your pump, the pump will shut off to protect it. But if you get a pump that pumps slower than your refresh rate, you won’t have to worry about drawing your water level down.
So those are the biggest factors you need to consider when picking out a well pump. There are some other more situation specific factors, but this covers the main ones to keep in mind. If you still have any questions or need clarification on anything, feel free to call one of our pump specialists at 855-560-5670.
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