How Do Magnetic Impellor Driven Pumps Function?

About magnetic impellor driven pumps

Magnetic impellor-driven pumps are completely sealed submersible water pumps. All are water-cooled and should never be run without water. Most need to be fully submerged for proper cooling. Overheating will cause the coils inside the motor to burn out; these cannot be serviced or replaced.

How it works

The current passing from the mains through the fixed copper coils generates a magnetic field. This causes the magnetic impellor (which is separated from the coils by a layer of plastic and held in place by a shaft) to rotate. The fan attached to the impellor also rotates and forces water out of the outlet, sucking water in the intake as it does so.

The impellor & shaft

The impellor consists of a magnet and fan. The fan should be firmly attatched to the magnet, but note that some fans are designed so that they can turn a short way independently of the magnet. This is to reduce the stress on the fan when the impellor starts or stops spinning. Impellors wll generally last longest if the pump is run continuously, stopping and starting cause the greatest wear. The fan can be broken however if foreign matter in sucked into the intake and causes the fan to jam while the impellor still spins. Impellors are replaceable, but usually only as a whole; fans and magnets are not available separately in most cases.

The role of the shaft is to hold the impeller in place so that it spins on its axis rather than moving laterally. There are two types of shafts. Set shafts are permanently affixed to the motor. These are commonly made of stainless steel. Removable shafts (as shown right) are not fixed but are held firmly in place, usually by snug-fitting rubber stoppers. Removable shafts may be ceramic or stainless steel. Steel shafts will eventually wear, although set shafts generally wear less than removable shafts. Removable shafts can be replaced, whereas set shafts cannot. If buying a pump with a set shaft, look for one with a thick steel shaft, since this will last longer. Ceramic shafts will not wear and can last indefinitely, but they are more expensive. Also, they must be handled with care, as they can snap if dropped or bent. For marine applications, ceramic is generally best since steel shafts may rust, although some pumps use high-grade stainless steel to prevent this. Always check whether a pump is recommended for marine use.

Servicing your pump

Magnetic impellor driven pumps require very little maintenance. However, you should inspect the impellor and shaft assembly for signs of wear once every few months, or whenever pump performance is suspect. At the same time, clean any accumulated mulm or debris out from the impellor well (the cavity in which the impellor sits), and from water intake and outlets.

Common problems

The most common problems involve the impellor, and are usually easily solved.

Problem: Pump does not run, ie. impellor is not turning

Possible causes & remedies:

  1. Check power supply, make sure filter is plugged in and turned on at the power
  2. Impellor may be jammed: gentle shaking will sometimes start the filter, but the impellor or impellor well may need to be cleaned.
  3. Faulty/worn impellor or broken shaft: check the condition of the impellor and shaft and replace if needed.
  4. Burnt-out motor or broken wiring: these cannot be repaired, you will need to replace the filter.

Problem: Impellor turns but little or no water movement occurs

Possible causes & remedies:

  1. Restriction of water intake strainer or prefilter: clean any debris from the strainer and/or prefilter sponge
  2. Faulty/worn impellor: Check the impellor, ensure the fan is fixed to the impellor (some spin and click, but should only have about a quarter turn free play), replace impellor if needed.
  3. Lift height too high for pump capacity: the higher up the water must be pumped, the greater the decrease in flow rate. Check the maximum head height, this should be at least twice the height to which you wish to pump.
  4. Restriction of flow by outlet hose or attachments: if the pump is attached to a hose make sure it is of adequate diameter as a narrow hose can restrict flow. Clean debris from the hose or other attachments with a flexible brush or pipe cleaner if clogged.

Problem: Pump produces excessive noise

Possible causes & remedies:

  1. Faulty/worn impellor or shaft: check the condition of the impellor and shaft and replace if needed.
  2. Restriction of water intake strainer or prefilter: clean any debris from the strainer and/or prefilter sponge.

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