FrankChong
Koi Lover
Aug 20, 2000, 3:45 PM
Post #2 of 3
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submersible versus external pumps
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Hi Benjamin,
External pump is more efficient and it last very much longer. In the water pump construction, there are 2 key components. The impeller and pump housing for delivery of water, and the electric motor which drives the impeller. The impeller is mounted on a shaft which needs to penetrate through the pump housing so that the motor shaft could connect to the impeller shaft. To prevent water from leaking out through the pump housing where the impeller shaft exit, mechanical seal is used.
In the external pump, when the seal is worn out, water could be seen to leak from the pump. New seal could be fitted and pump could still function. In a submersible pump, when the seal leaks, water would go straight into the motor, shorting the coil. When this happen, the submersible must be replaced.
External pump, especially the centrifugal type is more energy efficient than the submersible. However, swimming pool pump is known to be low in efficiency. Centrifugal pump has the advantage that the impeller could be trimmed to the exact diameter to deliver the flow rate you want for a given height of lift.
External pump discharge all its heat to the atmosphere via the motor fan. Whereas the submersible cools itself inside the pond raising the water temperature slightly.
However, the biggest draw back of external pump is the noise. I started with a 3/4 HP swimming pool pump on my 40 ton pond. The pond and filter chamber is adjacent to my house. The pump is so noisy at night I could not sleep. I had to replace it with 2 units of Omni-U which I found to be more energy efficient and delivers higher flow rate. I had shopped around but so far could not find one more efficient than Omni-U.
Please bear in mind that Omni-U is a low head pump. It works best when you do not lift the water higher than 4 meters. Over 6 meters no water would flow.
Where to install the pump ?
It depends on your design of filter chamber. If the elevation of your filter chamber is higher than pond you may have to install it in the first chamber. If filter and pond is at same elevation, the last chamber. Ideally you should design your system so that the pump would sit in the last chamber.
Flow rate.
For a 20 ton pond 200 liter per minute flow rate would be ideal, giving you water circulation of once every 100 minutes.
Water fall pump.
You should have a separate pump located at the last chamber of the filter so that only filtered water is pump back to the pond. You also need to connect the water fall pump to a timer so you could sleep at night and more importantly save electricity.
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