I am trying to areting my pond but air pump cost too much. I have an extra water pump available if I make two intake opening, one for water the other for air, would it work? or will it blow up the pump and kill all of my koi because it is made for pump water.
If you use a fountain spray you can add air by spraying water up in the air and letting it fall back into the pond. The best solution is to buy a pond aerator. They are available on line and at some garden centers. .
The only difference between a water pump and an air pump is the pressure difference between the two ends and hence across the longitude of the pipe. Air requires less pressure difference, it will pass across anyways. Now, if the pressure difference is too high (i.e. its a water pump perhaps) then the air will go past quite quickly and there is danger of actual overheating, as the kinetic energy of the air molecules will go very high. (Kinetic energy is proportional to temperature). Overheating results in possible hazards for the pond and also fluctuations in the pipe, whereas it COULD possibly (haven't done exact calculations) burst.
Here's is several reasons why it is bad idea to pump air with water-pump. There are differences in design of an air-pump and a water-pump due to a simple fact that air is compressible, and water is not. Water pumps are very poor at pumping air, so if the intake tube is not filled with water the pump won't be able to suck hard enough to bring it in. You can very easily damage your water pump, if you run it dry (meaning just pumping air), because without the resistance of the water, the motor turns too fast and also many pump designs rely on the water for its own cooling or lubrication. Pumps can temporarily work with some small air bubbles in them, as long as water is still flowing. This happens when running new-installed pump for the first time and it is normal unless it lasts for more than a minute or two. But even this small bubbles cause micro-strokes on shaft and bearings, shown through excess vibrations and audible gurgling or growling. In a long-terms, this causes so-called material fatigue and shortens the lifetime of a water-pump.
In general an air pump a water pump are two different types of pump though if your pump is a fixed displacement type, say a diaphragm or piston type pump it could possibly be used to pump air. If your pump is a gear or centrifugal type it will not pump air as it is designed for liquids only. It might tolerate a small volume of air in it but you could end up with cavitation damage to the components the air could cause the pump to lose it's prime that is the air in the casing could make the pump lose suction. What you might be able to try is using a venturi on the pumps outlet. That way you could use your water pump to pump water use the venturi to draw air into the water flow. Without getting too scientific a venturi is a smooth restriction in the pipe that speeds up the fluid (in your case water) flow in doing so it reduces the pressure energy of the fluid turns it into velocity energy. If the restriction is sized right it can drop the pressure of the fluid below atmospheric it will draw air or some other fluid into the flow. Perhaps the easiest way you could do it would be to use a round piece of stainless steel or brass (it won't rust) that is small enough to fit into the pump outlet (I'm guessing you're using hoses) bore a hole along the centre of it then bore a very small hole at right angles to it fit it into the line. It might take a bit of experimentation to get the sizes right but it should suck a bit of air into the line at the same time recirculate the pond water. Make sure there are no restrictions downstream of the venturi as the water will come out of it rather than the air being drawn it. Hope this helps.
