Fluid bed filter air line below water level

[netvine]

Hello, I am planning on building a fluid bed filter out of a 55 gallon drum to increase biological filtration on my ever expanding little aquaculture system. I am planning on using a hakko 25lpm and 2 cubic feet of alied aqua media. Around 1000gph gravity fed. I plan on using the birdman fluid bed filter diy method of a 3/4” bulkhead on the bottom to a 9” diffuser. My problem is I need to have the air pump in an enclosure close to ground level.

The main pond(s) will be above ground and so the air line will be below water level. I assume I will need a check valve for the 3/4” pvc connecting the Hakka to the elbow under the drum. Is this correct, and will it work, or am I making a critical error? Will. Is a swing check valve needed to reduce head or will any do in this application.

[icu2]

I never could find a 3/4" swing check valve... only spring loaded ones.
One fix would be just to bring the air pvc pipe up to the top of the barrel so it's over water level in the barrel and then
back down to the pump, making a loop above the water level in the barrel. The pond level shouldn't matter since the barrel
and air pipe is isolated to it alone.
Also a diffuser is made of rubber and expands when air inflates it and enlarges the holes in it to allow air bubbles to escape.
When the air is shut off the rubber contracts and closes off the air holes and leaves nearly no room for the water to escape.
I saw this when my pond aerated BD air line broke. I thought the diffuser had just plugged so it sat with no air flowing through it for
about a week. I got in the pond and removed the diffuser to test it and left the diffuser off the pipe overnight. I woke to found
the pond level had dropped by about 8"! It was because the air pipe was leaking and didn't lose water until I took the diffuser
off the pipe and that allowed water to escape the pond.
The loop in the pvc pipe though will give you assurance that water can't reach the air pump.

[cottagefog]

If you do a google search for boat bilge pump check valves, or dishwasher, or spa check valves you should find some SPRINGLESS check valves the size you are looking for.

Not sure if this is without a spring, but at least by the pic it doesnt look spring loaded. Goodluck!

https://www.pvcfittingsonline.com/3-...hoCnyUQAvD_BwE

[BWG]

Putting a loop above the waterline usually works - but not 100%. Never understood how the siphon gets started, but it sometimes does.

As Steve stated some diffusers advertise built in check valve engineered into the design. Also as posted above many no spring or low spring pressure check valves operating at 0.5 or less psi back pressure.

[netvine]

I’m gonna try the bilge pump check valve, if that doesn’t work I’ll run it over the barrel height. I really appreciate the help, Thank you all.

[CharlieQ]

Maxair makes a checkvalve for that application. I just built one last week.

[netvine]

Oh that is perfect thank you

[BWG]

Inline check valves are easy to find and most are not suitable. Valves restricting flow 0.5 psi or less are what's needed for low pressure pond air pumps. If the flow specifications aren't listed - don't buy. Good valves list operating specs.

1 psi back pressure is equal to 2.31 feet of water depth. Substantial reduction for a pond air pump.

FlexAir disc air diffusers advertise high flow triple integral cleck valve to prevent back flow.