Pond Boss Forums Thread Like Summary - Pond Aeration - Pipeline Considerations

I am not an aeration expert, and have no knowledge to add compared to the excellent advice our experts do give out on that topic.

However, I have "pipeline" experience, and there are several "best practices" for pipeline design that can significantly impact the efficiency of your aeration system.

1.) Water Build-up in the Pipeline

Consider your air pump early on a summer morning - pulling in air from near ground level. You have walked around many times and observed all of the dew on the grass. At that point your pump may be pulling in air with 70-90% relative humidity. That is a lot of water vapor going through your pump.

That air will be hot coming out of the air pump compressor so all of the water will be in the vapor phase. However, that air will cool significantly travelling down your air pipeline. (The soil temperature at depth at any location is close to the average temperature of your climate, so the ground will be "cool" relative to the summer air temperatures.)

Typically, the interior wall will start to "sweat" as the water vapor cools and condenses. These tiny droplets will continue to move along in the direction of the air flow. This is NOT a problem for a properly sloped pipeline.

However, this is a potentially large problem for a pipeline that contains any significant dips where the line goes down and then back up.

If there is a dip or sag in the pipeline, then those water droplets will move to that point and then begin to accumulate in the line. Over time, that entire dip will become filled with water! In a freezing climate and a pipeline not buried below the frost line, then that section of pipe will freeze. This is bad for two reasons. First, it will stop air flow to your pond diffusers. Secondly, your pump will be working at its highest possible pressure to try and clear the blockage. It usually will not be able to clear the blockage, so you will be creating severe wear on your air pump unless you have a high-pressure cut off switch.

Even if you are in a warm climate, the water-filled dip in the pipeline will steal efficiency from your aeration system. Typically, the pressure on the pump side will build up until it can push through the water and send the air on down the line. However, at typical aeration system flow rates and pressures, it does NOT push through at the full diameter of the pipeline. For example, in a 1" diameter pipeline it may be able to push through a stream of air only about a 1/4" thick at the upper boundary of the pipeline. For a twenty foot long dip, this is the equivalent of running a 20' section of 1/4" diameter pipe in the middle of your system. That always causes frictional pressure losses in the pipeline and a gauge at the pond end of the pipeline would now read a significantly lower pressure compared to the gauge at the air pump.

Solution #1: Always build your pipelines to have a gentle downward slope to the edge of the pond. You only need 1-2 degrees to keep those water droplets moving down to the diffusers so that they are blown out with the air.

If you have a gentle rise in the land at some point between your air pump station and your pond, then do NOT trench the whole route to be X inches below ground level. When you hit the rise in the ground level, trench that section deeper (relative to ground level) so that your pipeline run sustains a gentle downward slope.

Likewise, if you hit a soft spot while trenching or excavating, then check it with your longest level. If you did create a dip, then back-fill to ensure the proper slope through that section.

Solution #2: There are some situations that force you to have a dip in the line. Sometimes it may be a deep draw on your property, or it could even be due to man-made objects that cannot be moved. In that situation, pipelines use something called a blow-off valve to enable fluids to be removed from the dip in the line.

Basically a tee is installed in the pipeline at the very lowest point. A riser is then brought above the ground surface and a valve is installed. It works much better if a valve is also installed at the pond end of the pipeline. To operate, close the valve at the pond, and let the air pump pressure the whole pipeline up to the maximum "safe" pressure. You then throw the blow off valve wide open. This should create a big slug-flow of water, which should then turn to a mist as your hear the pipeline pressure drop to near 0 psi. Close the valve and repeat as many times as you are able to kick out fluid.

In summary, a gently downward slope on your pipeline is your best solution. However, a blow-off valve can help if you are forced to deviate from the optimal slope design.

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.]

"Normal" operating pressure will vary with diffuser depth placement and restrictions in the line/diffusers. Figure 0.5 psi back pressure for every foot of water depth the diffuser is placed. For Vertex diffusers/air stations, I SWAG at adding 1 psi to the open line back pressure. So, if you have one air station placed at 15 foot water depth and another placed at 5 foot water depth, you have to restrict the flow of air to the 5' deep air station to get air flowing through the deeper air station. I would expect to see 8 to 9 psi showing on the pressure gauge by the compressor providing your airline doesn't add to the restriction.

Rocking Piston Compressors are rated to work up to 30 psi, but the DIY'er will need to look at the specs and pressure/volume curve to see if the volume of air needed is available at the pressure that the system will run at.

Rotary Vane Compressors have a rated working load of 10 psi, but again, the DIY'er will need to look at the specs and pressure/volume curve to see if the volume of air needed is available at the pressure that the system will operate at.

Diaphragm Compressors that I am familiar with are rated to work up to 30 psi but the volume of air produced is the lowest of these 3 types of compressors.

In my experience, the easiest compressor type to rebuild is the Rotary Vane Compressor, followed by about a tossup between the Diaphragm and Rocking Piston types.

ALL compressors will die a quick death if they are not in an open area, or if in an enclosed area they need to have an added cooling fan pushing ambient air over them to keep the heat that they generate from cooking the bearings and electric motor.

Another thing that is overlooked by DIY'ers is intake air filtration and outlet pipe size. While many companies sell systems with 3/8" supply hose, I have found that the smaller hose increases back pressure and is a LOT more susceptible to building up water or condensation in the air line and freezing solid during the winter. Intake air filtration and regular cleaning of the air filter will increase the life of the compressor and will minimize volumetric loss. The deeper the air stations are placed, the harder the compressor has to work and the more stress is on the compressor if the intake air filter is restricting the incoming air.

Think of sitting down watching TV and breathing through a straw while you do it. Now imagine running while breathing through the same straw. The air compressor, just like you, has to work a LOT harder to get air through it.