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Answering Your Water Pump Questions

with RPS Engineer Mike

How do I choose HP for my pump?

Choosing a HP of pump isn’t as easy as saying “If your well is 200’ deep then you need a 1HP pump”, as there are a few factors that go into choosing what horsepower pump you need. Although total well depth is a big factor to consider, let’s highlight a couple of other important factors to consider. 


One of the other things, besides the total well depth, that you will want to consider is the amount of gallons per minute (GPM) that you want from your pump. With submersible well pumps you have two main parts to the pump, the pump motor and the pump end. The motor is what powers the pump end, and the pump end is what will determine how many gallons per minute you will get from the pump, as well as how many vertical feet of lift the pump is capable of pushing water. RPS carries one motor for every horsepower rating, but we have lots of different pump ends to choose from that will pump a range of gallons per minute. Keep in mind, a pump end that will push more GPM will always have a lower vertical lift than one that pushes less GPM. So a 10GPM pump end will have less vertical lift than a 5GPM pump end on the same 1HP motor. You’ll sacrifice vertical lift for a higher flow rate between. 


What if I want a higher flow rate?

Let’s take the example of a 1HP pump that does 5GPM. If you want a pump that has a higher flow rate than 5GPM, you will oftentimes have to size up to a larger HP pump in order to get a higher flow rate with the same vertical lift. Using our own RPS pumps as an example, the 05RPS20 is a 2HP motor with a 5GPM pump end that can push water a max of 1000’ vertically. In order to get the same 1000’ of required lift while increasing the GPM rate, you’ll need to jump to a 10RPS50, which is a 10gpm pump end with a 5hp motor. 



In a similar vein to how many GPM you want to get from your well pump, another factor to consider in choosing your pump’s HP is how many GPM your well is capable of putting out. Often called the well’s “refresh rate”, its the rate at which you well is capable of producing a certain GPM consistently. This will often be something noted on a well report after the well has been dug, as well drillers will often test the well and let you know how many GPM it is capable of producing. You will want to factor this number into your choice of well pump also, because if you have a pump that can pump 30GPM but your well is only capable of producing 3GPM, you will be pumping that well dry very quickly and could possibly damage your pump in the process. In certain cases you can make a system work if you have a pump that pumps more water than the well can produce, but you’ll want a controller with run dry protection and our RPS engineers suggest placing the pump deeper in the well if possible. Most of the time you will want to either pump slower than or match your wells refresh rate. For example, if you have a 300’ deep well with a 5GPM refresh rate, you would likely be better off with a 1/2HP pump with a 5GPM pump end, instead of a 1HP pump with a 10GPM pump end. So the refresh rate can play a factor in what HP pump to choose as well. 


All in all, the main things to consider when choosing what HP pump to pick will be your wells depth, refresh rate, and how many GPM you want to get from your pump. Be sure to always look at the pump curves to see if the pump you are looking at will work for your intended lift. But if you are still confused you can always call us and we can help you get sized for the best pump for your needs!

Previous article How do you match a pump to a motor?
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