Knowing the Basics

When working on a pump system of any size, basics in hydraulics and sizing always apply.

By Scott O’Brien

A 15 hp submersible pump is installed to be used in a pond near Lake Geneva, Wisconsin.

The past 22 years working for a pump manufacturer have provided me with a vast amount of experience and visibility to different pumping systems and territory changes, which proves a wide diversity of how a system changes based on geography.

I have traveled from Wyoming to Michigan and the Gulf of Mexico at different points in time. I have also traveled to South Texas where a pressure tank sits outside the house by the central air conditioning unit on a pad. Currently, I reside in Wisconsin where we have water lines buried just 6 feet deep. There is an amazing difference between pitless units to submersibles hanging on well seals.

But basic pump hydraulics and sizing apply to all of them.

Sizing Issues

The most rewarding part of my job is working towards a long-term resolution on a troubled install with multiple failures over time.

The most significant change I have seen over the years has been the introduction of constant pressure systems for residential and commercial use. This has been a positive change for the industry but generates a lot of calls, system start-ups, and issues that need attention on the system setup upon completion.

The same pump performance and sizing apply to a conventional system with a storage tank and pressure switch, compared to a pump/variable frequency drive installation.

The most problematic occurrence that manufacturers deal with on pump failures is the misapplication of a pump or one that is not sized correctly for the system that it is trying to operate.

The VFD installs are a little more finicky than a conventional system due to the VFD controller monitoring the psi, motor amps, speed of the pump, and so on.

The basic settings of most drives are the pump/motor has a minimum speed of 30Hz or half speed to lubricate the lower thrust bearing in any submersible motor. I have had a few calls where the pump was oversized so much that at 30Hz the pump would still build over 80 psi and shut the drive off, or in severe cases, damage the water lines.

A 40 hp submersible pump is installed at 600 feet on 4-inch pipe for a residential well system in Illinois.

The only way to resolve this is to pull the pump and install a smaller pump end with fewer stages so it will build less pressure. The contractor can use the same motor as it only loads the motor to the horsepower or amp requirements of the pump end.

I had one case where the new install was an 80-foot setting with a 1.5 hp, 20 gpm pump. The static water level was 4 feet, so the VFD could not slow the pump enough to not spike at 80 psi and would shut the system down. And as you know, this typically happens when a wife is in the shower.

Another situation I saw was an installation with a 3 hp, deep-set 7 gpm pump in a granite well that usually doesn’t produce much flow. This pump of any brand has a lot of stages or impellers that build pressure.

The well was not test pumped, so the flow estimate was based on prior wells in the area. This well had a static water level of 40 feet when starting the pump but only had about 20 feet of drawdown, so a pumping level of 60 feet on a flat lot with no elevation.

This would only require a 3/4 hp or 1 hp pump to perform adequately, but a 3 hp was installed based on the 600-foot water level that was estimated. This pump also tripped the VFD on overpressure as it couldn’t slow down enough to not make very high pressure. The pump was pulled and replaced with a smaller unit and is still operating today.

Speed Issues

A very interesting jobsite visit was after three pump failures on a 50 gpm, 10 hp install for a factory.

The installer called after the third pump failed prematurely and had a competitor’s pump on site and wanted a witness present to look for anything that could be causing the failures. The installation was in the middle of a factory that was built around the well and the walls were 30 feet tall. The crane used to pull the pump was massive to say the least.

We pulled the 120 feet of 2-inch galvanized drop pipe out of the well without breaking one joint or taking a coupling apart. The new pump was mounted to the drop pipe, cable spliced, and the pump returned to setting depth.

The water had a high iron content, so they wanted to pump the well clean for a bit, which is highly recommended on any installation before placing the well back into service. We set the pump on the well seal and put a 2-inch hose on the discharge to pump the water outside a door about 50 feet away.

Submersible pumps that have been pulled and replaced from coal bed methane wells. All photos courtesy Scott O’Brien.

I had an amp meter on the wire and told the maintenance manager to start the pump via the VFD that was not supplied by the contractor. He said it was running with no water, so he waited 30 seconds and then reversed the motor leads to change rotation, thinking the pump was running backward. There was still no water and fewer amps.

I had them stop the pump. I went around the corner where the motor control center was, started the pump, and saw that the controller was set for a two-minute ramp-up time. They thought slower was better to eliminate water hammer, but this was not getting the motor to one-half speed or 30 Hz in less than one second as required, let alone 15 seconds.

If the motor is not up to 30 Hz quickly, the thrust bearing in the motor gets ground up by the thrust pads with no water lubrication, drops the impeller stack, and destroys the pump end. I reset the VFD to 30 Hz minimum in one second and all has worked well. In fact, the installation has been in for more than five years now.

I told the maintenance manager that the factory owed the installer for three pumps/motors and three labor bills.

I loaded my equipment and left with a competitor’s pump in the installation. But now I have a loyal customer and one who looks at the entire system vs. just the pump.

Training is sometimes an expensive lesson. We all make mistakes but doing the same thing over and over and expecting different results is the definition of insanity.

Longevity Issues

My most interesting time in the field was probably covering Wyoming in the late 1990s and early 2000s when the coal bed methane gas market was developing in the state. I was a young salesman just starting for a manufacturer and was excited to see the country as well as something different from the normal 0.5 hp through 1.5 hp submersibles used in the residential market.

The same pump performance and sizing apply to a conventional system with a storage tank and pressure switch, compared to a pump/variable frequency drive installation.

The basic well construction was a 7-inch steel-cased well that was pressure cemented into the coal formation that varied from 600 feet to more than 2000 feet. After the casing was cemented, the driller under-reamed a 15-inch-diameter bore through the coal and left a couple of feet of undisturbed formation in the bottom of the well.

The coal was typically fractured and flooded with water, so submersible well pumps were installed in various ways to dewater the formation. The methane gas would rise to the wellhead under pressure and then was discharged through piping to a pod house where 30 wells merged. There, the gas was dumped into a pipeline for distribution.

The typical installs were 5 hp through 10 hp submersibles although some areas had 40-60 gpm, 25 hp deep sets for the same application.

The landowners were allowed to have a well every 40 acres, and their standard contract for these oil and gas leases featured a 1/8th royalty. After a few years, some of the ranches that had sections of land and a few hundred cattle suddenly had some serious income beyond their expectations.

New welded pipe fencing, new pickup trucks—the F-350 King Ranch Editions were the most popular choice—and paved driveways a mile long were suddenly common.

I got invited by one production company to travel with the pump installation crews for a week. They were hired labor and performed all the new and replacement wells. The production company supervisor wanted a report on how the crews performed and ideas on how to make pump failures less frequent.

We traveled to one jobsite where we pulled a 40 gpm, 10 hp submersible that was 883 feet deep and replaced the pump, motor, wire, etc. The pump was controlled on a VFD with a transducer to keep a certain water level in the well.

The crew told me they had replaced this pump/motor combination “every other day” for a year and a half! I thought, “Excuse me?” The pump failure was repetitive because after the well was pumped off at 40 gpm, the formation slowed, and the VFD slowed the pump to only 8 gpm.

The coal formation continually sloughed off small particles of coal, so with the pump installed on 2⅜-inch tubing, there was not enough velocity to pump the particles out. This eventually bridged off the flow, dead-headed the pump, and another failure would occur.

After the week and witnessing dozens of installs, I had a meeting with the supervisor. I suggested that for this one well in particular, we should try a 2 hp, 10 gpm pump, and install it on a 1¼-inch drop pipe to get the velocity up.

He looked at the pumping foreman and asked if they were making money doing it the way they had been doing it all year. With methane gas going for $8000 to $9000 per day out of one well at the time, the foreman said of course, so they continued to install 10 hp pumps in that well as well as many others.

There was no thought as to system requirements, longevity, or anything other than pumping water as fast as they could to produce all the gas they could in a short period of time. I was selling the pumps and motors, so I didn’t argue the point.

But after gas prices were reduced to $2 or less per sales unit, installation costs started getting scrutinized heavily, and more efficient and properly sized pumps were installed. The market, like any petroleum boom, had a bust and most of the wells now sit vacant or are used for livestock water. It was an amazing time while it lasted and a great experience I will remember forever.


I was told by an elderly gentleman when I was a pup in the industry that I may never see a time when water is cost-prohibitive to pump but will probably see a time when it will be cost-prohibitive to treat. At times, I feel we are headed in that direction with contaminants like PFAS and others in the news today.

The regulations have tightened over the years on well construction, grouting, plugging, and production. It is all for protecting the groundwater that so many take for granted, that we make our living from, and that we must educate to all that it is our most precious resource.

Scott O’Brien is the senior area sales manager at Pentair Flow Technologies. His sales include water well submersibles, jets, large centrifugal, sub and lineshaft turbines, VFDs, and wastewater products. He has worked in the water well service industry since 1982 and began by working in the field for a pump installer and water well driller. O’Brien can be reached at scott.o’