Pond Boss Forums INTRO Questions & Observations Pond Aeration - Pipeline Considerations

2.) Pipeline Diameter and Fittings

One of the fundamental aspects of engineering is determining the trade-offs. There are pipeline engineers that can calculate all aspects of the pipeline characteristics to create the optimal design. Unfortunately, we cannot feasibly do that on our basic aeration pipelines. Therefore, I can only give out some basic principles, and then you must compare that to any trade-offs in your specific pipeline system.

Trade Off #1: In my recent research, electrical cable is significantly more expensive than polyethylene flexible coil pipe. Further, the voltage drop over a long electrical run is a much greater percentage than the drop in air pressure over a long pipeline run. There is literally no "trade off" to running more air pipeline in your aeration system compared to electrical line. The initial installation cost is lower AND the long-term operating cost is lower due to the higher efficiency.

Safety is a further bonus. Cutting an electrical line with an implement can be a safety risk. Cutting a low-pressure air pipeline is typically not a safety risk, you just need to repair your "oops".

Finally, this consideration is even MORE important for solar systems. The voltage drop is even greater as a percentage loss in low voltage systems. Therefore, for solar aeration systems, you need your air pump as close as possible to your solar panels, and then use your air pipelines to more efficiently transfer the air to the diffusers in the pond.

Trade Off #2: When you pump a fluid through a horizontal pipeline, the pressure at the outlet is always lower than the pressure at the pump discharge. This is due to something called "frictional line losses". This problem is much worse for "incompressible" fluids. The people that have observed the behavior of pumping water through long pipelines, hydraulic fluid through hoses on their tractor, etc. will have some feel for these pressure losses.

The frictional pressure losses (at low pressure) for a "compressible" fluid like air are much less than for the fluids described above, but they still do occur.

When I have priced polyethylene pipe for the long run to the pond, I have frequently been a bit shocked about how SMALL the price increase is moving from 1/2" to 3/4" to 1" piping. The pressure losses on your aeration system will be dependent on the air volume, the pressure, and the pipeline length and diameter. If you look at the pump chart for your compressor, you should be able to observe how much your flow rate goes down for each additional psi of "back pressure". It may turn out to be a good trade off to pay a little bit more on your initial cost for a larger diameter pipe for your main run to get a little more flow rate at your diffusers AND save on some wear and electrical costs since your pump compressor works less in a system where it does not always have to overcome an additional 1 psi in pipeline pressure losses.

Frictional pressure losses in pipelines for compressible fluids (air) become MUCH more significant as the pipeline diameter decreases relative to the volume of gas being transported. For example, for a typical aeration system pressure and volume, you would probably barely see the difference at your gauge on the outlet end over a 200' pipe run if you moved from 1" pipe up to 2" pipe.

However, the small-diameter weighted lines in the pond are a different matter. The price difference for larger diameters can be significant. (But the differential has seemed to come down to me over the last few years. Our installers on the forum would know better.) You MUST work with a proper design person at this stage to get the correct volume of air to the diffusers to operate your system! Even if the smaller diameter weighted line gets up to within the design spec window for your diffusers, you still might be better off to pay a little more for the installation to increase your diameter by one size traded against higher pressure losses created in the smaller ID line over the entire lifetime of your system.

Trade Off #3: Every time you add a 90 degree elbow in your pipeline system, you cause a tiny bit of pressure loss. Other fittings, such as internal barb pipe connectors cause even greater losses. You can usually have some trade offs to minimize these losses.

For example, instead of installing an elbow in your system, you can trench the line in a gentle curve to get back on the same route. A little bit of extra length on your pipe is less of a pressure drop than adding an elbow. Further, every fitting you add is another possible leak point. [Low pressure (100 psi rated) polyethylene pipe does have a tendency to kink. Any turns in the pipeline MUST be gentle enough to avoid kinks.]

If you are installing a 280' air pipeline, then it is best to buy a 300' coil rather than make up the distance with your scraps from previous projects. Some types of piping have external connectors that do not reduce the interior diameter (ID) of the pipe. However, most piping is connected using some type of internal barb connectors and exterior clamps. This will cause a pressure drop in your pipe.

Personally, I believe this is a trade off to avoid. Always use the connectors recommended by the manufacturer. The worst pressure loss you can suffer is a leak in your pipeline connectors!

Finally, I like having "extra" valves in my pipeline systems. They give you more control of your system outputs. For example, if you install a tee off your main pipeline to run a diffuser in the pond at that location, and then there is an additional 500' of pipeline to your second diffuser, that diffuser may not have enough pressure and/or volume to operate properly. A valve installed just beyond the tee to the first diffuser would give you the option to pinch the valve a bit and tune the two diffusers to optimal operating conditions.

The trade off in that situation is to pay a little extra for your valves to get the "full opening" variety. That type of valve will have a little bit less pressure drop in your system when in the "full open" or mostly full open position.


[Please feel free to make any additions, clarifications, or corrections as needed.]