An external pond pump offer several advantages over their submersible counterparts. They are much easier to access for routine preventive maintenance or repairs. They are generally more durable than submersible pumps and have a longer useful life cycle. External pumps are also available in more powerful sizes than in-pond pumps. They are especially appropriate for high-flow water features, such as waterfalls, and filters that are pressurized that may need a powerful amount of water for a good backwash and not to forget to mention they are also good for ponds with a large volume of water to circulate.
The best benefit of an external pump is ease of access. There is no need to worry that leaking oil will contaminate a pond and kill fish. External pumps are easily hidden from view with standard landscaping techniques and do not mar the scenic beauty of a pond setting. Water is usually drawn to the pump in large diameter piping, and leaves and twigs are caught in a filter basket placed just prior to the pump. It is extremely easy to monitor and empty an external filter basket. Prior to the priming basket and it will depend on your application a pre-filter should be used in your installation to keep fish and other objects from entering the piping to your basket. When using a pond skimmer no pre-filter would be necessary.
While submerged
pond pumps are less expensive, external pond pumps have longer useful life cycles. This usually equalizes the cost when figured over the useful life of the pump. In-pond pump motors are sealed away from water, and most are considered disposable. When they stop working, they are replaced. External pump motors may be able to be repaired by the mfg.
Larger flow capacity is often equated to higher operating cost, but energy use should not be the only consideration. Larger pumps are typically fitted with larger piping. Larger piping moves larger volumes of water with less frictional loss. In practical terms, this means that the pump moves larger volumes of water by doing less work. It is quite feasible to run a large external pond pump and use less energy than a smaller pump that must work harder to move the same volume of water. This can make external pumps the more economical choice for circulating large ponds.
External pumps for ponds also have some disadvantages. The most significant disadvantage is the priming requirement. Unlike water, air is compressible. Any air gap in the flow of water can cause the pump to lose suction. To avoid this possibility, external pumps usually require a self-priming device and or a check valve below the surface of the water. They may also be placed at a grade below the surface level of the pond to facilitate priming.
