PART 3: Circulation

In the last installment we discussed circulation a great deal. The reason circulation is an important topic is that everything that lives in the pond depends upon circulation or lack of circulation. Water circulation takes place both in the pond and outside the pond. To circulate water outside the pond it requires a force on the water to get it to move. This force commonly is either gravity, a pump or air.

Gravity and pumps are commonly used to circulate water outside a pond and are usually used in conjunction with each other. A pump is used to either lift water above the level of the pond so that gravity can be used to move it back to the pond. Or a pump sucks water out of a container attached to the pond, such as a skimmer or vortex settling chamber, and gravity returns water to the container to replace the water that has been removed.

Now I would like to discuss pumps. Pumps are usually classified as one of two types; submersible and external. Submersible pumps are designed to run submersed in water. If they run out of water, they will over heat. They are usually located in the skimmer or in the pond. Most submersible pumps are filled with oil to transfer the heat from the motor to the water. They usually have a life span of less than four years if used in a pond. It is usually not recommended to rebuild submersible pumps. Submersible pumps are easier to install and less costly. For these reasons, submersible pumps are used in ponds.

External pumps are located outside the pond and are cooled by the air. If an external pump is submersed in water it will short out the motor. External pumps use air for cooling. They usually have a life span of 7 to 10 years and normally can be rebuilt with no problem. External pumps are generally more energy efficient.

Regardless of the pump used, it should be matched to the application. Another concern is the amount of energy consumed as the typical pond in this area runs about 8 months a year, 24 hours a day and seven days per week. What sounds like a good deal when you buy the pump could end up not being the case.

How do you determine what is the best pump for your application? This is not a simple matter. First you must determine exactly what the application is and how much water will be required. Then the static and dynamic head pressure the system will have must be calculated. This can then be matched to the pump curve and that will determine which pump will work in your application.

Another means of circulating water is the use of gravity. Gravity is a constant force that pulls toward the center of the earth. Since water is a fluid, gravity is always going to try and pull the water to the lowest point it can flow to until it is contained. Once water is higher than the pond, as long as there is a path for the water to flow back to the pond, it will flow there. This is how a skimmer works or how a waterfall works. If you are using gravity to move water through a pipe, the sizing of the pipe becomes critical. In this case you should consult with an expert to make sure the diameter of the pipe is the correct size. Gravity is the cheapest way to move water but may not be the most efficient.

Using air to move water is a very efficient method if moving the water to a very limited height. The devices used are called air lift tubes. An air stone is placed in a body of water and then a pipe is placed over the air stone. The air going up the pipe moves water with the air out of the pipe. This can move a lot of water.

Why would water be circulated outside the pond? Some possible reasons could be to run a waterfall, stream, or filter.

I have discussed water circulation and equipment extensively for one reason; the better the circulation, the better the pond is going to operate. The poorer the circulation, the more problems there will be with the pond.

In the next installment I will discuss filtration.

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