Aquarium Setup #5 – April 1993

Air Pumps

 by Dr. Steven J. Schiff

 

            If you had to rate aquarium hardware by its sex appeal, the lowly air pump would be near the bottom of the list.  It wouldn’t be as far down as, say, feeding rings or tank dividers, but it’s safe to say that most aquarists don’t get totally turned on by an air pump.  I’m sure that if Porsche designed air pumps, this would be different, but unfortunately they don’t, so try to remain calm.

            Air pumps, despite their relative absence of sex appeal, are one of the most ubiquitous accessories utilized by aquarists.  What they lack in physical attractiveness, they more than make up in aquacultural usefulness.  They can be found lurking near almost every fish tank in the world.  All too often, though, they are purchased as an afterthought or without much advance planning.  As is the case with almost all aquarium equipment, careful selection and setup of the air pump will result in maximum performance, longer life, and lowest-cost operation.

            There are three major categories of air-pumping devices used in the majority of home aquarium setups.  For the largest installations involving multiple tanks and lots of air, there are rotary air blowers.  These provide the greatest volume of air and can serve dozens of tanks simultaneously.  They are noisy and consume a fair amount of electricity, so they are used only when the sheer number of tanks and amount of air required warrants it.

            Piston pumps form the second category.  These were very popular several decades ago, when their pumping volume and pressure could not be matched by the noisy and underpowered vibrator pumps that were their chief alternative.  Piston pumps are still available in both one and two cylinder models, but they have largely been superseded by the vastly improved vibrator pumps which form the third category.  No longer noisy or underpowered, vibrator pumps are available in a wide variety of models, sizes, and designs.  Their high performance and (generally) low cost makes them the overwhelming choice for home aquarium use.

            In selecting a pump for your particular setup, you should choose one that can provide enough air to run all the air-driven accessories in all the tanks it will be servicing, and then some.  It is better to buy a pump that’s too big for a given application than one that’s too small.  The output of a larger pump can always be reduced to a lower level if necessary, but an underpowered pump will never give satisfactory performance and will have to be replaced.

            One problem in choosing an air pump is that there are no uniform standards for rating them.  Some manufacturers rate their pumps by the pressure delivered; others by the volume of air.  A few indicate what size tank or how many accessories can be served by a particular model.  This latter system would be very useful if it were uniformly applied, but different manufacturers have different ideas of how much air is required by a given tank, or how many accessories will be used in a tank.  Unfortunately, all too many manufacturers give no idea at all about the output of their pumps.

            Ideally, the output of an air pump would be rated by both volume and pressure.  A high-volume pump is useless if it cannot deliver its air against the pressure produced by the water in the aquarium.  Similarly, a pump that cannot deliver a sufficient volume of air is inadequate, even if it produces high pressure.  With your specific setup in mind, you can decide on a pump by enlisting the aid of your aquarium dealer, who can help you decide how much air you need, and which pumps will provide it.

            Two factors affect the back pressure which must be overcome by an air pump which is forcing air through an air-line tube and into an underwater accessory (such as an airstone.)  The first is the water depth, i.e., how far underwater is the accessory?  This determines the water pressure that must be overcome by the pump in order to force air through the tube.  It is independent of the accessory.  In a 10 gallon tank, the water depth is 12 inches, and the water pressure at the bottom of the tank is 0.45 lb. per square inch.  In a 55 gallon tank that is 18 inches deep, the water pressure is 0.68 lb. per square inch.  Even at a depth of four feet, the water pressure is less than two pounds per square inch.  These pressures are easily overcome by aquarium air pumps.  A typical high-output vibrator pump, for example, can exert 7.5 pounds per square inch.  Smaller pumps develop less pressure, of course, but should have no trouble pumping air to the bottom of any home aquarium.

            The other factor, of course, is the accessory itself: how hard is it to force air through the airstone?  This varies from accessory to accessory and is more difficult to quantify.  In general, though, the smaller the opening through which air must be forced, the greater the pressure required.  In addition, the pressure required to run the accessory usually increases with time, as the air passages become clogged and dirty.  Not only does this reduce the air flow and decrease water movement, it can actually damage the pump!  The diaphragm of many vibrator pumps can tear if the back pressure becomes excessive.  For this reason, it is important to keep your air-driven accessories clean, and change the disposable ones when the airflow becomes visibly reduced.  (One common test: change an airstone when you can no longer blow through it by mouth.  However, I suspect that pump damage can occur even before airflow resistance becomes this high.  So change your airstones before you think you need to.)

            Assuming you don’t have an enormous fishroom that requires the services of a rotary blower or similar specialized air supply, your choice is essentially going to be between a vibrator and a piston pump.  Although the vibrator type is the overwhelming choice today, let’s not dismiss the piston out of hand, but carefully evaluate the advantages and disadvantages of each.

            1.) Noise.  No air pump is completely silent, but some of the better-made vibrator pumps (especially in the smaller sizes) are very quiet.  Piston pumps have very quiet motors, but the operation of the piston produces a bit more noise.  Overall, a properly operating piston pump should not be any more noticeable than the low hum of a vibrator pump of comparable output.  Modern air pumps of either type are not particularly noisy.

            2.) Cost.  Because there is such a wide variety of vibrator pumps available, it is difficult to generalize (since when has that stopped me?)  The price of these pumps varies with size, quality of construction, and reputation of manufacturer.  In general (see?), a vibrator pump will cost somewhat less than a piston pump of comparable output.

            3.) Ease of repair and maintenance.  Normal maintenance (which I will discuss shortly) of both types of pumps is easy to perform and can be done by most aquarists, even those who are not mechanically inclined.  This is also true of the most common types of repairs required on vibrator pumps..  If the motor of a piston pump requires repair, however, it is no simple task.  (Fortunately, these motors are very durable.)

            4.) Availability of spare parts.  While this is usually not a problem for any brand of pump still in production, the widespread availability and enormous popularity of vibrator pumps gives them an advantage in this area: many pet shops keep frequently-used parts and repair kits in stock.

            5.) Vibration.  As their name implies, vibrator pumps vibrate.   While it usually doesn’t lead to excessive noise, this vibration can cause the pump to “walk” or gradually creep across the surface on which it rests.  These pumps usually have flexible “feet” on their bases which are intended to dampen the vibration and minimize this problem, with varying degrees of effectiveness.  Piston pumps usually don’t suffer from this.

            6.) Electrical consumption.  The motor of a vibrator pump has but a single moving part and is very efficient.  A typical medium-to-high output vibrator pump consumes 5 watts of power; a typical piston pump of comparable output consumes about 11 watts.  In addition, the more complex motor of the piston pump produces a significant amount of heat — enough so that good ventilation is a consideration when installing such a pump.

7.) Output.  The piston pumps that are currently available all have a fairly hefty output, both in terms of pressure and volume.  To run a small aquarium – one or two airstones, a box or sponge filter, etc. – they are overkill.  There are many small vibrator pumps that will perform this task efficiently, quietly, and at low cost.  When a higher output is needed, of course, a piston pump is a viable alternative to a vibrator, and the two should be compared according to the features that most affect your own situation.

            As with most mechanical equipment, proper maintenance of your air pump will enable it to last longer and operate more efficiently.  There are simple maintenance procedures that are required for each type of pump.  The motor of a piston pump should be oiled regularly and kept free of dust.  Keep it away from flammable substances because it can get hot.  The leather washer that caps the piston should be changed occasionally to maintain an airtight seal.  The external drive belt wears and may periodically require replacement.

            In a vibrator pump, the diaphragm wears and eventually tears, whereupon it must be replaced.  Excessive back pressure (as from failure to change airstones) can hasten this process.  The valves wear out and must occasionally be replaced.  If the pump has an air filter, the filter should be replaced when it becomes dirty.  All of these operations can be performed without a high degree of mechanical aptitude.

            Some vibrator pumps have a rotary control that regulates the output.  These make it very easy to control air flow and deliver precisely what you need to your system.  If your pump lacks such a control, you may still regulate the air flow by inserting a valve in the air line that bleeds off as much air as necessary.

            Unlike much aquarium equipment (such as heaters, filters, lights, etc.), the location of an air pump is not terribly critical.  You can put it anywhere nearby the tank (as long as it is not in the tank).  Very long runs of airline tubing may reduce the output somewhat, but this is rarely a problem.  If the pump is located below water level, however, it is a good idea to install a check valve in the air line.  This is a valve that allows air to pass one way in the line, but closes if the direction of flow becomes reversed.  If a pump located below water level should fail, an somehow water finds its way to the highest point of the tube, a siphon can start which will allow water to run out of the tank until the siphon is broken.  If your accessory (an airstone, for example) is located near the bottom of the tank (the most efficient placement for an airstone), the tank can be nearly emptied in this way.  This is not conducive to fish health, and a check valve is effective, inexpensive insurance against it.