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Frequently Asked Questions About Submersible Pumps

Quick Answers

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    • A submersible pump is a pump that is designed to be immersed in fluid. The motor on a submersible pump is attached directly to the pump body, allowing the whole assembly to be submerged.

    • A submersible pump has a system of mechanical seals that prevent fluid from getting into the motor, resulting in short circuits.

    • A submersible pump typically has the shape of a cylinder. The sealed motor of a submersible pump makes up the lower half which is connected to an above ground power source, controlled by wires. The upper half is the actual pump which is comprised of a series of impellers, each separated by a diffuser, that force fluid up a hose or pipe.

    • A submersible pump may fail for the following reasons: Tank size is too small, Short cycling, Running dry, Lightning strikes, Improper selection of high head pumps in low head applications.

    • A submersible pump is used in many applications. A single stage submersible pump is used for sewage pumping, slurry pumping, drainage, and general industrial pumping. A multiple stage submersible pump is lowered down a borehole and used for water extraction or in water wells.

    • A submersible pump has the reputation of being exceptionally reliable. The technology of submersibles is well developed, resulting in few problems and difficulties. It is not uncommon for a submersible pump to function well for 25 years before requiring service.

    • A submersible pump is best serviced by a professional, in that the whole unit must be extracted from beneath the ground for inspection.

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Why use a submersible pump for your garden project?How to choose the best submersible pump

A submersible pump is ideal for outdoor water projects such as fountains, waterfalls, spouting ornaments, ponds, and water gardens.  Corrosion resistant pumps are available for use in salt water.  Using a submersible pump in a Koi or other fish pond allows you to retain more fish, and maximizes the health of your aquatic plants.  Also, a submersible pump is the most economical way to circulate water in your pond or other water feature.  It is placed directly in the pond and usually must remain underwater in order to operate.  An important feature of a submersible pump is that it is quiet and virtually free of distracting noise.  It can also be used to drain your pond when necessary.

Be careful to read and follow the instructions of the manufacturer if you install the submersible pump yourself, because there are many variables to be considered. A regular outdoor electric outlet using an all weather extension cord is satisfactory to power the pump, or a submersible pump can work off a generator when plugging in is impractical.  A magnetic drive pump, which avoids the use of coolants, eliminates the possibility of pump seals rupturing and spilling oil coolant into the water.

There are numerous sizes and types of pumps, therefore it is advisable to seek some guidance in choosing a submersible pump for your project.  Some factors to consider are:

  • How high will the pump have to lift water?
  • Will there be filters?
  • How often can you clean the submersible pump?
  • How many years do you want the submersible pump to last?

For help in choosing the best submersible pump for your water feature, feel free to contact us.

Choosing the best submersible pump for your unique needs will save significant time and money in energy costs and down time.  It is prudent to consider future needs when determining your usage requirements.  Do you need a submersible pump because you are going to install a pond on your property or purchase a herd of dairy cows?  Maybe you work in the wastewater industry and need to select a submersible pump suitable for that particular application.  Installing a pump that is larger than you need is a waste, since the life of a pump is determined as much by starts and stops as it is run time.

It is important to understand how the motor works on a submersible pump to properly evaluate its effectiveness.  The best pump is equipped with a motor that works below its load limit.  You never want your submersible pump to do more work than its motor can handle.  The full load amperage or FLA rating of the pump is vital.  This rating is one of the best indicators of the amount of work the motor shaft is able to accomplish.  The type of impeller used on a submersible pump must also be taken into consideration.

It is important to know the pump head correctly.  The head is a measure of how much pressure a submersible pump can develop.  Head is measured from the surface of the water or other material to be pumped.  Usually a submersible pump box will provide the maximum head information, but often pump flow rates at different heads or heights is not indicated.  A centrifugal submersible pump usually pumps less water as the head is increased.  At maximum head, the flow from any pump is zero.

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How to install a submersible pump in your wellHow to size a submersible pump

Before installing a submersible pump, the pump should be wired, immersed in a container of water and operated.  Taking these measures insures that the pump is in proper running order.  The type and the size of drop pipe used for submersible pump installation is dependent upon a number of factors:  The depth to the water and pumping level, the amount of pressure that the submersible pump can attain, the allowable friction loss in the drop pipe, and the weight of the submersible pump.

Follow the steps listed below to install your submersible pump:

  1. Warm the pipe with hot water (less than 65 degrees C) before making adaptor connections for the drop pipe. Do not use a torch to heat plastic pipe because the polyethylene will crystallize.
  2. Double clamp all connections of the submersible pump with 100 percent stainless steel clamps. Screw heads should face in opposite directions.
  3. Use a nylon safety rope with a bowline knot to install the submersible pump. After it is in place, the rope can be tightened and tied securely at the top of the well casing. Doing this minimizes the free fall distance in the case of a pitless unit or pipe failure.
  4. Insert the electric cable to the pump into a 3/4 inch plastic pipe to prevent the cable from rubbing the well casing.
  5. Protect your submersible pump from power surges or lightning strikes. Pumps with one horsepower motor or less usually have built-in protection. If your pump does not have this protection, you need to wire a lightning arrestor to the line conductor and back to the electrical grounding system. Consult an electrical inspector for electrical grounding details necessary for your submersible pump.
  6. Close the restrictor valve nearly all the way before starting the pump. Start the pump and slowly open the restrictor valve until the unit is pumping at full well yield, at rated capacity, or begins pumping sandy water. A submersible pump will wear out rapidly if it pumps sandy water. Sometimes, using the restrictor valve is all that is needed to prevent sand from being lifted up into the pump. The pump should never be shut off while pumping water mixed with sand. Instead, the submersible pump should be restricted until the water is clear.

Every submersible pump is manufactured and designed to operate within certain parameters.  As the pump works against rising pressure, which is converted into feet of head, the pumping capacity falls.  Alternately, as head falls, pumping capacity rises.  The pumping capacity versus the total head form the engineering curve of a submersible pump.

If a submersible pump is operating to the left of its curve or is undersized, there is too much head against the pump.  Conversely, if a submersible pump is operating to the right of its curve or is oversized, there is too little head against the pump.  It is, therefore, very important to achieve balance in order to secure optimal functioning of a pump.  Listed below are some recommendations to follow when sizing a submersible pump:

  • Demand requirements for the system should be ascertained. If the well capacity is determined to be insufficient, modifications to the submersible pump system are indicated.

  • Testing procedures should be performed to acquire the draw down and pumping level.

  • Expected flow rates, pipe sizes, and total piping runs should be evaluated to calculate the friction loss of the submersible pump.

  • The maximum and minimum total dynamic head or TDH should be discovered.

  • The submersible pump should be sized to function within the optimal efficiency specifications of the manufacturers' performance curve.

  • The velocity of water flowing past the motor should be determined. If the flow is not sufficient to meet manufacturers' cooling regulations, a flow inducer should be installed.

  • Water temperature does not affect verify motor horsepower on a submersible pump, but a rated motor horsepower is necessary if pumping water at elevated temperatures.