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How Do Garden Pond, Fountain & Waterfall Pumps Work?

Probably all pond pumps whether used for fountains, waterfalls or filters are what are generally called centrifugal pumps. All centrifugal pumps behave in the same kind of way ...

  • Electric power to the pump motor turns an impellor at high speed

  • The pump impellor has a series of small chambers separated by vanes and the vanes are designed in such a way that they almost scrape the circumferential pump body in which they are turning.

  • On each revolution of the impellor water contained in each small chamber is discharged by centrifugal force through a "gap" in the body of the pump and a pipe is attached to this gap so that the water can be directed to the falls, filter or fountain arrangement.

  • Because the vanes are rotating at high speed the water flow through the "gap" appears continuous

  • Water flows into the small chambers through a central aperture called the pump suction .... this central point must be kept clear at all times for the pump to perform efficiently and effectively. To prevent blockages the suction is almost always inside a type of slotted cage or body and in many cases there is a foam sponge inside the body cage which prevents even small particles getting into the vanes of the rapidly circulating pump impellor to prevent possibly breaking the impellors.

What Makes The Pump Impellor Turn?

Electricity flows through wires totally enclosed in a block of resin to insulate the wires totally from any possible contact with water and thus make the pump safe for immersion in the pond water .... safety is of critical importance and is why a complete waterproof design is essential. This need for absolute safety means that if the pump electrics fail then the pump cannot be repaired.

Electric current that flows in wires surrounding a magnet creates a turning force so the body of most fountain or waterfall pump impellors consist of a cylindrical magnet through which a ceramic or stainless steel shaft runs. As soon as the power is switched on the magnet turns around the shaft (which remains stationery) and the impellor which is permanently attached to the rotating magnet then also turns at the same speed as the magnet.

The vanes of the pump impellor in small fountain pumps tend to be straight while larger pumps have curved vanes ... the curvature increases the efficiency of the pump meaning more water can be delivered to a greater height using less or equal power.

If you remove the impellor always be very careful especially if the shaft is ceramic ... a pump shaft made from ceramic material is very hard and allows the life of a pump to be extended greatly BUT the shaft is brittle so handle with care. Most shafts sit inside rubber or plastic bushes to hold the shaft rigid and in a central position. These bushes are small and can be easily lost.

While holding the impellor gently turn the vanes and generally you'll find they only turn in one direction (especially if vanes are curved) and trying to turn them in the opposite direction the vanes come up against a stop. The reason for this is that electric current is oscillating and in practice therefore a rotor could go clockwise or anti-clockwise depending upon phase position. If the vanes initially start to rotate in the wrong direction the "stop" forces them to turn back in the opposite direction.

What Can Go Wrong With My Garden Pond Pumps?

Modern UK pond pumps from companies like Hozelock, FishMate, Blagdon, and Oase are almost perfect. These pumps run day in and day out if looked after and will last for many years ... most pumps these days have 3 years guarantee and this is indicative of reliability. However there are occasional problems that can be summarised as follows ...

  • The impellor shaft breaks during handling ... replace impellor shaft only.

  • The vanes become detached from the magnet ... buy new impellor (the test here is if the impellor rotates in both directions fully and pump flow is greatly reduced or zero).

  • Suction becomes blocked ... remove restriction. If pump has sponge this blocks with algae and after a while it blocks every day. At this stage replace sponge. Our suggestion is always get a modern pump without sponge or one that will probably run happily without the sponge in place.

  • If the pump does not deliver any water flow and the impellor is fine and correctly seated in the bushes then the motor is probably burned out and as such the whole pump would have to be replaced.

  • You can safely close a valve on the delivery side of a pond pump but always make sure the suction remains completely open and free of restrictions. Any restriction on the delivery side will reduce pump flow ... e.g. kinked pipes, bends, too many connectors and too small a diameter tubing or pipe will all restrict water flow. Always minimise the length of tubing or pipe used between the pump and the filter or waterfall. Excessive pipe length will lower flow rate (measured in gph or gallons or litres per hour, lph).

How to choose the right pond pump

An important article has been written in this regard. In essence you decide the right pond pump by considering 5 things ... We suggest you read the pump comparison article here and also remember using 2 pumps is often cheaper and always better than running 1 if you have fish especially

  1. Determine the optimum pump flow rate

  2. Optimize pump head (pressure) by removing any obstructions to flow and minimising actual height to which you want to pump water

  3. Purchase price of the selected pump

  4. Running cost of the selected pump which is mainly the cost of electric power

  5. Guarantee period and value of the pump guarantee (read the instructions)



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