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How to kill a well pump

By Steve,

(This is a technical blog, and this article has to do with water pressure and is intended to save you from burning up a well pump and clue you in on the factors surrounding a well pump.)


There's a lot more to know about water wells than meets the eye.

Our well pump got hit by lightning and we took the opportunity to upgrade from a 2 to a 5 HP pump. Researching pumps, I learned that you can get a Chinese pump for as little as $100-150. I suspect there is a lot of branding going on for every actual pump manufacturer as many look the same. But they are not all made the same, indeed the life span are often a hit and miss. The leading quality brand is no doubt Gould (if you ask professionals who install them for a living). Gould have some 2,900 employees in 20 global locations and manufactures a wide variety of pumps.

We made a GREAT deal on one with a retail of over $2,500 that can lift water from as deep as 600 feet, which BTW is called headroom, or just head. A main consideration with pumps is in how high it can lift water (against gravity). There is of course the amount of water in gallons per minute and (gpm) it will pump, and the pressure it can generate measured in pounds per square inch (psi).

One important thing to bare in mind with water is that, unlike air, it does not compress. This is why it can hurt hitting water. You have to push it away since it does not "give".

This means when you push water through a pipe and the pipe size changes, it will still have the same amount of pressure. The amount of water flow will change but, again, since it does not compress it retains the pressure.

As you probably know we have 10 acres of land in which we do irrigation as well as feeding water to the house. These can be wildly different needs in terms of volume of water. So choosing a proper pump can be tricky.

A submersible pump is made out of two distinctly different parts. One is a motor which spins the pump, mounted on top of the motor. The other is the pump which these days have many stages, each one accelerates the water faster and faster. Ours have 22 stages.

Our motor is manufactured by Pentair, the same maker as the top pool pump brand, while the actual pump is made by Gould. It has a five year warranty and are known to last 15-20 years if properly used.

That brings us to our first pump which was installed when we bought the place. It too was a 5 HP pump but it was not being cared for properly at all. What we did not know is that a smaller pump up to 2 HP needs to run for at least 1 minute to cool down after what is a hard start that instantly heats up its coil. Repeated heating up without the cooling will eventually start short circuiting the coil in the motor.

For a 5 HP motor that means a minimum of 2 minutes of run time.

Our original 5 HP pump ran for however long it was needed without any concern about two minute minimum run-time. No doubt it got worn out by not getting the cooling time it needed.

While researching a new pump I poured through a LOT of information to educate myself sufficiently to be able to make educated decisions.

The new pump can produce 135 psi and over 100 gallons/minute - A LOT of water.

To save the pump from starting and stopping with each small use of water a clever design was made called pressure tank. It allow us to draw water from the tank without needing to turn on the pump. Once the tank is empty the pump fills it up and turns off.

So far so good. Remember the 2 minutes minimum running time? We have two pressure tanks that stores 66 gallons of water. The new pump fills them in 28 seconds. Yes, that is less than a quarter of the run-time we need.

It was recommended to us that we should get a Cycle Stop Valve to slow down the filling of the tanks. More research.

It is a $1,100 piece of metal. There are two large competitors one named their model Cycle Stop Valve, which became the common name for the function. The other one is called Cycle Guard Valve, I found a dealer that sold me one for $350 to be rid of the last one (which his clients were too small to use and so it just sat there).

It did slow down the water but, at the expense of putting up the maximum back pressure on the pump each time it came on also causing the pressure relief valve to spit out water for a split second.

On my design I had placed a pressure gauge on each side of it to see how the different the pressures were.

(A simplified layout of the water flow from the well to the house, where O is the gauges):
Well--O--Cycle stop valve--O--Pressure tanks--<to the field/house>

I came out to check on it one time and found that there was zero psi on the pump side while 58 psi on the other side of the Cycle Stop. If you paid attention you should go "-What!?" You cannot have zero pressure on the inside (where the pump is) and 58 psi on the outside (leading out to the field and house). Upon closer inspection the needle in the gauge had gone all the way around the dial and was sitting on the backside of the pin, where the needle rests when there is no pressure.

In other words I was looking at something like 130 psi on the pump side of the Cycle Stop and only 58 on the other side.

The tanks warranty is good up to 75 psi, and they are tested up to 100 psi. Fortunately I only had 58 psi on the side of the tanks.

But, it meant the well pump was running at maximum pressure. Generally that's not what you want to do. So I started looking for a different solution.

We do a fair amount of water catchment with over two thousand gallons total storage capacity across different locations on the farm. For that we use potable IBC totes. Each holds 275 gallons.

My math told me that if I added a tote to the equation it would add enough time to easily pass the minimum two minute run-time. The challenge lied in how to add a non pressurized tank to two that were pressurized? My solution applied a permaculture maxim of re-purposing when applicable. I had an old pool pump. It's a 1 HP pump which is OK with having short run-times and is made to push volumes of water horizontally with minimum of head room (remember that from the top?)

It turns out to be producing 36 psi and a fair amount of water. In fact it delivers as much to the house as the expensive well pump some 86 feet below ground. It does not have to lift water (no head room) and so becomes an efficient solution.

It works so well we are considering replacing the pressure tanks with another IBC tote which will give us the ability to draw 550 gallons without using the well pump.

The well pump can actually run literally for months, but needs those two minutes to cool down the motor coil. The run-time for two totes is estimated at 10 minutes.

This also equates to much fewer starts which will extend the life of the pump.

At some later point I will probably replace the pool pump with a boost pump but for now I have a working solution.

To automate the well pump turning on and off you use a pressure switch. What is not clear is that they generally only support up to 2 HP pumps. A bigger pump will simply wear out the contacts causing it to fail.

That explained the number of broken pressure switches I found in the pool house from the previous owner. When it became clear that switches that can break the 5 HP pump are not readily available I solved it by adding a relay, which is able to break eight times as much. Now the original switch only breaks 1/2 Amp instead of the 30 Amps the well pump draws, greatly extending its life span.

You adjust the pressure switch for the pressures needed to turn on and off. Three most common values are 20 on and 40 off, 30-50 and 40-60 psi. I had adjusted mine to come on at 28 psi and off at 58 psi, a 30 psi spread.

When you have a pressure tank it is set at, for example, 38 psi and the pressure switch is then set to start at two psi above (40).

The pool pump in this configuration is however not operating at a spread like the well pump but is sitting at 30-36 psi. A pressure switch needs 10 psi spread to work and I'm not getting that. So instead I'm putting in a water flow switch will will turn on when water is being used and off when not.

In the end we lift the water to the tanks above ground and then draw water from them as needed.

If you reach out I can fill you in more on the details.