A Guide to Submersible Pumps

Tue April 23, 2019 - National Edition
Joe Moser, Chicago Pneumatic Power Technique


Choosing the correct pump for the job at hand will eliminate the biggest and most common missteps during the pump selection process.
Choosing the correct pump for the job at hand will eliminate the biggest and most common missteps during the pump selection process.
Choosing the correct pump for the job at hand will eliminate the biggest and most common missteps during the pump selection process. Dewatering pumps pump fresh water with minimal folic, such as sand.

What are you pumping? This is a key first question to ask when it comes to electric submersible pumps. It seems simple, but too often it is left unanswered while the wrong pump is purchased or rented. Ultimately, one wrong decision could lead to an even bigger mess to clean up.

It is a crucial factor for the contractor to understand the type of application in which the pump will be used. Just as important is taking the time to see what elevation, distance and flow are needed on the job. Otherwise, they will likely choose the wrong unit to perform the work.

Answering these questions correctly will eliminate the biggest and most common missteps during the pump selection process. To avoid costly mistakes, below is a guide for buying, maintaining and using submersible pumps.

Buying and Renting Decisions

Applications

Electric submersible pumps are best utilized in deep ground water. There are a few varieties of these pumps and it is important to select the correct one:

  • Dewatering pumps: pumps fresh water with minimal folic, such as sand
  • Slurry pumps: pumps a heavy mud
  • Sewer pumps: handles everything in a sewer

The operator will know instantaneously should they choose the incorrect pump. It can create a host of issues including: clogging the pump, snapping the shaft, breaking the impeller and completely wearing the webbing down.

Once the user knows the correct pump style per their application, they should determine the following: amount of flow needed, elevation change and desired distance for moving the water.

Elevation change determines the pump strength necessary to overcome gravity resistance. It is important to know both the suction elevation from the water to the eye of the impeller, in addition to the discharge elevation from the eye of the impeller to the water's destination. By adding these two numbers, the user will have the sum total elevation (gravity resistance).

The distance determines if the line size should be increased to reduce friction loss because of friction resistance. Friction occurs in all pipe and hose when liquid travels through it. Two things impacting friction are the velocity of the water traveling through the pipe or hose and the overall distance of the pipe or hose to the delivery point.

By understanding how far and to where the water is going determines the flow required. The distance an operator needs to move the water and the elevation change both make a difference due to friction losses.

Knowing these three variables make it fairly easy to select the correct pump.

Features

Identifying the variables will also impact the submersible pump's features, such as horsepower (hp) and type of impeller.

  • Size and Power: Incorrectly sizing the pump for the application is often one of the biggest mistakes on the job site. This includes having too much horsepower (hp) and not enough flow. Selecting the wrong size can lead to seal, impeller and shaft failures
  • Type of Impeller: The user will want to know the metallurgical makeup of the impeller — stainless steel, hard chrome or cast iron. The impeller type is crucial. For instance, if the operator is pumping something with solids in it; they would want a solid handling impeller style and a submersible that can pass the solid
  • Pump Casing: The outer material of the pump casing, aluminum or stainless steel, can be beneficial depending on the material being pumped

pH Levels on a Scale of 1-10

The casing and metallurgical make are important for chemical compatibility. If the water has a low pH, which can be acidic and corrosive, the operator will want a metallurgical material based on what is being pumped. In this case, stainless steel is a good choice for lower pH levels. Additionally, aluminum handles a pH level between five to seven, but pumping low pH will eat the casing to its death.

Maintenance

Dewatering pumps pump fresh water with minimal folic, such as sand.

A little proactive maintenance goes a long way, and this is especially true for submersible pumps.

For starters, it is always important to consult the original manufacturer's guidelines. This in turn will help the operator create a proactive schedule of daily tasks and specific-hour intervals.

For daily use, the most important thing is to make sure the submersible pump is not clogged. By doing so, check to see if there is anything against the screen and clean when needed. Also, inspect the cable cord for cuts.

The nice thing about submersibles is they are not equipped for engine oil, which drastically reduces maintenance on the pump compared to other pumps. However, we recommend periodically checking to ensure the seal has an appropriate amount of oil.

Lastly, by simply running the submersible, an operator can observe the unit and make note of leaks, abnormal sounds or smells.

Safety Precautions

Electricity is always dangerous. By sticking something electrical in the water, it is imperative to provide safety for the pump and for the people around it. So, it should always be the operator's first priority.

First, it is important to always properly shutdown the pump before performing any maintenance and system checks. Another safety measure includes making sure the pump does not rotate in the wrong direction.

One of the biggest dangers operators face with electrical pumps is an exposed cable. When a stray current in a motor uses a bearing as its path to ground, the resulting damage is known as electric arcing. This develops if there is a difference in potential between the shaft and the bearing housing.

For instance, if an operator runs a three phase submersible pump, they would have a L1, L2, L3 and ground. An arc could occur anywhere between L1 and L3, creating an electrical surge or a fry situation back towards the electrical motor.

Successfully matching the pump to the job starts with some upfront work. Finding answers to the application, elevation change and distance questions will ensure it flows smoothly without any hiccups.