The primary purpose of delivering air into a pond is to increase the level of saturated oxygen. Aquarium type diaphram pumps usually stop making bubbles at a water depth of 1 or 2 feet. The longer that a bubble is in contact with the pond water, the more beneficial is it's effect.
Our piston pumps are constant displacement types. They deliver their full output to deep Koi Ponds. This is a used, factory rebuilt, piston type air pump with a 30 day warrantee.
These were originally very expensive pumps used for medical applications. .
We've tested these and they will drive two 12 inch long air stones at a seven foot or greater depth.

That is a lot of air, sufficient for Koi Ponds to 10,000 gallons or more.
We don't always have these available. Quantities are limited. Please ask us to confirm stock before ordering.
Normally stocked in two configurations, open and cased. They both use the same pumps, but the cased units are enclosed in plastic boxes that will protect them from the weather. The open style are the pumps with a three leg cushion mount and open switch and cord. These are used where they will be installed within an existing weatherproof housing.
Pumps run cooler this way, with larger space for cooling air circulation.
These pumps are fan cooled and use replaceable piston rings and reed type valves.