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Answering Your Water Pump Questions

with RPS Engineer Mike

What size pump do I need for my well?

In order to choose the right size pump for your well, you will need to know some information about your well first. You will use these pieces of info about your well and your intended setup to narrow down the field of pumps to ones that will best fit your needs. The main things you will need to know are well depth, how many gallons per minute you would like to get, and what you will be pumping the water into. Once you have these pieces of info, you can get a good idea of what size pump you will need for your well. 


Unfortunately, there isn’t a clear cut range of depths where you can say “if your well is between X and Y feet deep, you need a Z horsepower pump”. Of course, deeper wells will usually use higher horsepower pumps, but there just isn't a hard rule to follow. The reason for this is because different pump ends that push more or less gallons per minute will have different depths where they are able to perform at their best. Let's take a 200’ deep well as an example, if you wanted a pump that will pump into a storage tank and get you 5 GPM, you would use one of our ½ HP pumps. But if you wanted to get 25 GPM out of that same well, you would need to use a 1.5 HP pump. When you want to get more GPM from a pump, you will sacrifice vertical lift in order to get a higher flow rate (given that the motor is the same HP rating). In order to get higher flow rates from the same depth well, you will have to go to a higher horsepower to be able to maintain the same lift. 


You also need to take into account where the water is being pumped to. If you are pumping into a pressure tank, you need to make sure to factor that into the total lift that the pump would experience, as having to push against the back pressure of the pressure tank will add additional lift. The equation you need to know is that 1 PSI = 2.31’ of lift. So if your pressure tank is a 60 PSI pressure tank, then you will have to add 138.6’ of lift onto the lift the pump has out of the well. So if we take the previous example of a 200’ deep well and pump into a pressure tank instead of a storage tank, now the pump is experiencing the 200’ out of the well, and the 138.6’ from pumping into the pressure tank, making the total lift that the pump is experiencing 338.6’. This is very important to factor in, as a pump that can do 200’ of lift may not be able to do 338.6’ of lift. Oftentimes people will buy a pump they think will work in their well, only to hook it up to their pressure tank and have the pump burn out as it is trying to pump water but just doesn’t have enough power. 


Hopefully you found this page useful. If you still have any questions or need any clarification, feel free to reach out to one of our pump specialists at 855-560-5670.

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