Air Pumps - What you need to know

When buying an air pump, you want one that is quiet, low in power usage, while continuously delivering enough air to your pond.

To get the reliability, the pump must be able to do the work demanded of it.

When exerting the pump beyond that specified point, it will heat up, shortening its working life from a few years to a few months. It is therefore well worth the effort considering some aspects of using these pumps and air stones for aeration.

Air pumps - What you need to know



To help you choose the right pump for your application, some aspects using the specifications of a Waterfall LP-100 as an example are presented:


Meaning of “Max Pressure: 0.042 MPa”

Pressure is usually quoted in MPa (note 1)

A pressure of 0.042 MPa equals 0.42 bar or 420 mbar equals 6 psi. It also happens to be equal to 4.2 meters of water pressure (mH2O) at standard conditions i.e. the pressure exerted by a column of water 4.2 meters high or exerted on any bubble from an air stone placed at a depth of 4.2 meters in the pond.

That means, if at a depth of 4.2-meters, ZERO air escapes from the air stone, you will have NO aeration. In that condition the air pump will work hardest yet deliver no air. This will cause the pump to heat up while significantly shortening the life of the rubber diaphragm. Once the diaphragms are torn, the pump becomes ineffective. Mechanical damage can very quickly occur thereafter with unpredictable consequences.

Every pump comes with a work curve specification from which you can deduce the pressure and air output relationship. (See the graph below)

For example: At a depth of 1.5 meters (0.015 MPa) the LP-100 should deliver 120 litres per minute. 7200 litres or 7.2 m3 air per hour.


air pump

Rule of thumb is not to operate the pump above 80% of the stated maximum pressure. For continues work operating at a pressure of 20%-60% of maximum pressure is advised. That is theoretically the most economical point of operation. For a more accurate figure you should consult the relationship between work done (air pressure) and electrical power (Watt) used for that specific pump, information normally only available for larger pumps.


Meaning of Max Air Output: 8400L/hr

8400 litre per hour is 140 litre per minute.

This specification is at the other end of the scale. No pressure. No point in running a pump for no reason is there?

You will notice an ‘open’ pump has a different sound. You should not run the pump in this condition for an extended time. It will not last.

Use the curve to determine the flow you will get for your set-up.


How warm is too warm?

The easy answer is when it is too hot to handle. If you cannot pick a pump up with both hands and hold it for 10 seconds, it is too hot.

It is standard for us to employ an adjustable valve to bleed the excess air if the pump is getting hot. It can also be a matter of an under-specified air pump; in which case you must invest in a bigger model.

Since conditions can change, it becomes good practice to also check the temperature of your air pumps whenever you do your weekly or monthly filter maintenance.


Why would conditions change?

Air stones tend to clog up. This is due to environmental dust that passes through the air filter and (blown) into the air stone. Fine pore air stones are more likely to clog, and the low-cost grey or blue mineral sand types are particularly vulnerable. It is recommended that these types of air stones are replaced every 8 to 12 months.

They cannot be cleaned and failing to replace them can lead to damage to air pumps.

Glass bonded air stones are more expensive, have medium sized pores that take longer to clog. The upside is that they can be cleaned and used for many years.

Air stones also clog due to bacterial build-up and must be subjected to the same cleaning treatment from time to time.

For more information on cleaning air stones, please contact us.


These pumps use efficient electromagnetic linear diaphragm technology. Used widely for aeration of aquaculture and garden ponds, natural swimming pools, bubble baths, wastewater treatment, deep water septic tanks and commercial and industrial water treatment. 

Understanding how to get the best pump for your application will be well worth it.


Servaas de Kock

September 2019


  1. MPa, megapascals with a capital while mPa is millipascals which is a unit minute unit 109 times (1 with 9 zero’s) smaller
  2. A work curve of an air pump shows the relationship between the work done (air flow output) for a given load (pressure).