Pond Boss Forums AERATION Systems questions Reduce or Enlarge pipe size for aeration?

Here is my puzzle. I am running a GAST 1/4 hp (model 0523) pump to a 1/2 acre pond. My run is about 400'. I am temporarily using my 1 1/2" PVC water line for 300' then reduce to 1" PVC for the remaining 100' then distribute into the pond through 1/2" poly tubing running 3 diffusers (4', 6' & 8' deep). Works great but I can't keep using the 1 1/2" water line, so...

My question:
Does the order of pipe size from the compressor make any difference? Run 100' of 1" PVC reduce to 300' run of 3/4" PVC to 1/2" poly line distribution points OR reversed - 300' of 3/4" to 100' of 1" then to the 1/2" poly tubing?

I was told 3/4" PVC should be ok for my 400' run but I would like to use up the 100' of 1" PVC.

Based on a middle-aged EE who was forced to take two ME classes 25 years ago:

If you are going to use 300' of 3/4" and 100' of 1" - it shouldn't make any difference which size you feed through first. The resistances/frictions created by each separate section are additive, regardless of order.

Theo has it correct. You can make the run of 400' with 3/4". Any larger pipe in the 400' distance is okay too. We just ran a total of 750' for a 3/4 hp rotary pump. System has 450' of 3/4" with 3 laterals of 1/2" and then 300' of 1/2" to last diffuser. System is operating 4 membrane diffusers and all working good.

Friction Loss in 400' of 3/4" is 0.12 psi. In 1" the friction loss is 0.08 psi. If you have enough 1" line, I would use that and reduce it to your 100' of 1/2 poly pipe.

At 8' of depth, your pressure is 3.5 psi. Adding the 0.08 psi (400' of 1") + 0.16 (100' of 1/2") to the depth psi of 3.5 you will have a total of 3.795 psi. I do not know what the back pressure of the type of diffusers you are using so you may see even a little bit higher number on the pressure gauge as a result from the diffuser back pressure.

A Gast 0523 is designed to operate at a continuous pressure of 10 psi. You should have more than enough pressure for your system. Happy ponding!

The air guage that tecman is using would not even probably register the combined pressure loss (0.2-0.4 psi) of the piping he is using. As Cary said, considering the pond depth, long airline and diffusers he should have plenty of psi available from the Gast 0523.

Thanks to Theo, Bill and Cary for your input.

I finished the install. From the pump I ran 325' of 3/4" then 3' of 1" to first valve, 60' to second, then 60' to last one. From each valve I ran 1/2" PVC or poly to the diffusers. My first diffuser puts out the most air and declines as it moves down the line. My diffusers are DIY so it's tough to say how much cfm each is putting out. The guage at the end of the line shows 3 psi with all valves open and 5 psi with the first one half closed. The guage at the pump shows 10 psi. I also added a fourth diffuser to a small pond about 30' from the pump.

I don't know what these numbers mean so my fine-tuning will have to be done by sight. First impression is there seems to be some good action, especially from the first diffuser.

Should the most powerful diffuser be in the deepest (8') or shallowest (4') part of the pond?

Thank you again for your assistance.

Tecman,

The deepest diffuser should have the valve open all the way. Use the remaining two valves to even the "Boil" size for all three. The shallowest run would require the least amount of pressure.

Again, having different type of diffusers on the same line may take some time to even out the flow.