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Elephant

Insufficient air flow problems

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Having some trouble getting adequate airflow to the diffusers in my deep water culture beds. I have three DWC's 1.2M X  18M, with 17 diffusers each for a total of 51 spaced roughly every meter down the length of the DWC's. The water depth in the DWC's is a constant 20cm (8"). I am running two 60 M3/hr ring blowers. Appropriately sized PVC pipe connects the centrally located blowers with a length of PVC that runs down the side of each DWC. Each diffuser is connected to the PVC pipe via a one meter length of 1/8" airline tubbing. The diffusers are 10" long by 1/2" wide, encased in plastic, but open on one side.

I was barely getting any airflow from the diffusers with one ring blower, so I recently added a second. There is some improvement with the second blower but the performance is still disappointing. I have confirmed the air filters are clean and the airflow from the blowers feels appropriate in terms of strength or volume.

I understand the ring blowers are not suited to develop very much pressure but I would have thought 20cm of water would be acceptable.

I am wondering if it's an issue with the diffusers? They are about six months old but don't seem to be any less effective than they were originally.

I am reluctant to add another blower as my electricity allotment is already reaching it's maximum. Especially without evidence that this is the problem.

I understand a diffuser consumes roughly 0.3 cfm. So, if I am calculating correctly,  0.3 cfm X 51 diffusers = 15.3 cfm required, and my two blowers produce 60 M3/hr, (1 cubic foot = 0.0283168 cubic meter). This works out to 0.43 cubic meters per minute, or 26 cubic meters per hour required for 51 diffusers. Considering each blower is providing 60 M3/hr in theory, I should have over four times the airflow required. So what gives? Is 20cm of water too deep for a ring blower, are my diffusers cheap Chinese junk, or is it something else?

Edited by Elephant (see edit history)

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It might be that the static head & hydraulic head combined is close to the max head of the blower. Single stage ring blowers are design to move a lot of air with very little back pressure. Do you have the pumpcurve (head vs flow) for the blower?

Also do you have any restrictions in the suction line? such as air filters/non return valves etc as they can reduce performance substantial.

Try to run the blowers in series: one blower outlet connected to the inlet of the next one (you create a 2-stage blower). But be careful that the blowers get enough cooling as the airtemperature will go up. 

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