Deep Well Pumps

Choosing the right submersible pump for your water well

“Hmm, which of these pumps should I buy? This 1 HP FPS well pump or this 1 HP Goulds well pump?” Many folks are scratching their heads about purchasing a well pump while searching at the hardware store or online. There are many variables involved when selecting the appropriate submersible well pump for your home. Some water wells are over 800 feet (250m) deep while other wells are 80 feet (25m) deep. Water demands vary from just a few gallons per minute to hundreds of gallons per minute depending on if you are supplying water for a small cottage or a large estate. In this overview we are going to explore the factors affecting the selection of the correct submersible well pump for your water well. If you are interested in where to buy quality submersible well pump equipment, check out this article before you buy equipment online or at a hardware store!
Aren’t Pumps sized by Horsepower?

Don’t fall into the trap of thinking you need a certain horsepower of pump. You’ll notice the two amazon links to the right for 1/2 HP pumps. One of these pumps flows 5 GPM and the other flows 10 Gallons Per Minute! Is this just a mistake or oversight in the description? No! These pumps have different impellers and create different flow and pressures! A 1/2 HP 5 GPM pump creates more pressure and less flow than a 1/2 HP 10 GPM pump. In the pump industry we typically designate pumps by both the flow rate and horsepower required. Another, more precise, way to designate a pump is by what is called the “design point” of the pump. The design point includes the flow rate needed and the amount of pressure (head) that the pump needs to produce. When specifying the correct pump, it is more important to specify the amount of pressure and flow required than the horsepower required for the motor. Some pumps may be extremely efficient and be able to provide the flow and pressure with less power and thus require a lower horsepower motor than their cheaper competitors. While a more efficient pump may cost more, remember that it is working for several hours each day. The cumulative power savings over the next 7-10 years will more than pay for the more expensive & efficient pump when you factor in the decreased energy consumption. The cheap pump may be much more expensive in the long run.

Now, you’re probably asking. OK, I get it, choosing a pump by simply looking at horsepower can be very problematic, so what do I do? How do I know how much pressure or flow is required? We’re glad you asked! Hang on because now we’re going to help you understand how to calculate the design point and then choose a pump based on the design point, then we’ll finish up by giving some examples of pumps available online that seem confusing and help give you some of the tools you’ll need to make sense of it.
The optimal pump is the one that delivers the water and pressure needed while keeping the pump operating in the optimal efficiency zone.
If you look at the 2 HP pump curve you notice this pump will struggle to keep up with both pressure and flow demands and it is highly likely it will work outside of the “optimal efficiency zone” shown in the blue background of the pump curve chart.

Now let’s look at the 5 HP pump curve. While this pump can meet the flow and pressure demands, its expected area of operation also falls outside of the blue efficiency zone on the right hand side. Another significant factor is that larger pumps cost more money! This large pump also requires larger wire and larger pipe to hold the increased weight of this size pump, pipe, water & wire. When you add up the larger pump, wire, & pipe you may have more than doubled the installation costs. A bigger, higher horsepower pump is definitely not “better” in this case as it will hurt your wallet for the initial purchase and keep your wallet skinny with unnecessarily low efficiency/high energy consumption in the future. In addition, if the well cannot provide 20 gallons per minute, the pump could over-pump the well and start to suck air! This could damage the pump and it would then need to have a special controller installed to turn it off when it runs out of water. The “bigger is better” mentality creates lots of problems and expense down the road and should be avoided! When in doubt, BIGGER IS NOT BETTER when it comes to submersible pumps.