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Article 09: Pond Basics - Pumps, by Jeff Richardson

Posted by Jeff Richardson on

Pond Basics - Pumps (Article 9)

Depending on the how much water volume your pond or water feature will have, and how much flow you want or need, or how much elevation changes you have envisioned for the system, a proper pump will be needed to meet all these aspects.  The pump needs to be efficient and reliable above all else!

Anatomy of a Pond Pump: Most pumps have an electric motor which turns a shaft which is connected to a housing containing the impeller.  The housing will have a water inlet and discharge.  When the impeller spins, it produces suction on one side and pressure on the other.  Many pumps can be damaged if the impellers spin backwards from the direction the motor turns OR if the pump runs dry.  Submersibles usually cool themselves by exchanging heat with the water they are submerged in.  External pumps usually have large finned bodies and exchange the heat with the surrounding air.  Many submersible pumps are asynchronous.  This is a fancy term meaning they will spin the impellers faster or slower depending on the amount of power they are fed.  Therefore, a motor rheostat can be installed to control the flow of power to speed up or slow down the pumping action.  Many external pumps are centrifugal in nature.  This means if the water backpressure on the intake or discharge side slows the pumping action down, the pump will use less power – very efficient!   As pumps are designed to move water, most need to be filled with liquid before switching on (priming).  Some pumps will self-prime given some water.  Others may need you to fill them with water first.  Attaching a primer pot to the intake side of the pump helps in this endeavor.  This is nothing more than a sealed cylinder with lid that you can open and fill with water.

Choosing a pump: This is not simple as it depends greatly on your water feature.  A submersible may be just fine for running a fountain, small stream or pondless waterfall with the pump residing in the cistern at the end of those features.  A large external pump may be needed to move large quantities of water in a system which has a large volume in order for it to turn over the entire contents of that pond once an hour.   But no matter what type and how many, you want to buy a RELIABLE pump that comes with a good multi-year warranty by a reputable company.  Also read reviews from pump owners.  They can tell you what their experiences were when they had something go wrong and how easy or much of a hassle it was to get corrected.  Look for pumps that are for continuous operation as well.  Read online instruction manuals for the pumps you are considering.  For instance, submersibles may need to be cleaned out on occasion.  Read on how difficult it is to do.  I have seen some pumps come apart without the need for tools while others you need many to perform a very tricky maintenance procedure.  Do you homework! 

Head Charts: Most pumps come with a head chart.  What this tells you is how many gallons of water an hour (GPH) or a minute (GPM) the pump can flow at maximum (little or no head height).  Head height refers to the height above the pond you are moving the water.  If you are raising the water one foot, the head height is one foot.  As you increase the head height, the amount of GPH or GPM reduces.  The size, length, smoothness and number of turns in the plumbing all reduce flow as well beyond this head height.  As a rule of thumb, every ten feet of tubing add 1’ of head height, every 90° fitting (or four 45° fittings) add 1’ of head height, and every check valve adds 1’ of head height.  Even the size of the plumbing will cause backpressure as well (larger is better).  Round-up and find a pump (or combination of pumps) that will move the entire volume of the pond once an hour (one and a half times or twice an hour is better).  When looking at different pump models, try and target a pump with your total head sum, and moving enough volume of water (target 1-1/2 to 2 times) somewhere in the middle of the chart.  You want the pump to comfortably move the water (not push it to the extreme top-end of what the pump can do). 

Previous Article: 08: Pond Planning – Sizing Components

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