Rethink your method to weight down the PVC. Even consider using another type of pipe such as 1/2" or 3/4" polyethylene black irrigation type pipe. Do not overweight your underwater airline. You may need to remove it in 1, 5, 10, 15, 20 yrs. After 10 years the cement blocks could be completely submerged in pond muck. Any excess weight will make the line removal or adjustment job cause a lot of cussing and wishing I would not have done that. For 1/2" black poly and 5/8"ID garden hose (both same ID) it takes 1/2 lb of weight per foot to keep it on the bottom same and 5/8" ID weighted airline -100ft weighs 50 lb. For weights consider stranded cable wrapped around the hose, homemade weights of used galvanized pipe, rebar-rerod, heavy chain, bricks strapped to the pipe, PVC pipe filled with cement. Use just enough weight to hold it on the bottom - no more. Diffusers should be lifted each year and cleaned despite what sales promos tell you.
Airline ID really depends on the amount of air volume you are pusning through the pipe. For up to 5cfm you can use 5/8" no problem for all airline runs up to 500ft. Branches can be 1/2"ID. I operate an equivalent of six 9" membrane diffusers (3 stations) with my 0523 GAST rotary vane pump all with 5/8"ID airline.
One diffuser(tube style) that I remove each winter receives air from a 5/8"ID good quality garden hose with life-time guarantee (consider kink proof style). I use it as a demonstrator. Hose is non-weighted and floats until it has to sink from weight of the diffuser&base. Whenever this floating hose sinks, I know the check valve is sticking-leaking at the diffuser allowing water into the airline. It has been operating very well for 16yrs; still going strong. I install it with a boat and remove it in November by pulling on the hose.
Last edited by Bill Cody; 01/03/17 02:37 PM.
