Downspout Airlift: Rectangular

A 3"x 4" Plastic Downspout as a Rectangular Airlift Riser

I had been chatting via email with a friend in Australia for a few days. His hobby is designing and building hydrofoil surfcraft (for the past 20 years). I mentioned I was working on developing an airlift pump project.

He was very interested in airlift pump technology and wanted to test it in a 5,000 liter “plunge pool” that he just installed. He came up with a simple, off-the-shelf item to make a small prototype rectangular airlift riser for testing purposes – a 3”x4”, plastic downspout.

I calculated he would need about 1.7 cfm airflow injected at 30” (100% airlift submergence) using a 1/2"-3/4" inner diameter (ID) horizontal injector cylinder. The water pumping rate should be 70% higher than a single 3” ID airlift (@ 1.0 cfm air) and the same or slightly more than a single 4” ID airlift (@ 2.0 cfm air).

(Looks like 3”x4”, rectangular vinyl downspouts are available at Lowes in 10’ lengths.)

I came up with a compact horizontal injector configuration for a 3"x4" downspout riser (picture below).  This injector would be connected to two (2), 1/2" ID  air delivery lines branching off a 3/4" ID line.
I used 3/4" npt x 1/2" barbs; 3/4" 90 elbows, S x FPT, Sch. 40 PVC; and 3/4" SDR-21 (thin-wall) PVC pipe.
The 3/4” SDR-21 PVC pipe provides more ID than Schedule 40 pipe, for low resistance air flow.

[The same could be done with 1/2" PVC pipe and fittings (last picture).]

Click the following links for:

Wurts, W.A.  2012,  Rectangular Airlift Pump Design Outperforms Cylindrical Units.  Global Aquaculture Advocate,15(6): 77-78.

3" x 4" Vinyl Downspout

https://www.lowes.com/pd/Amerimax-Tr...out/1000244803  

Alternate 1/2" ID horizontal injector configuration requiring 3/4" ID air delivery line.

Airlift Pump T-injector with 3-Hole Air Injector Disk

Airlift Pump with Air T-injector Modified to include a 3-Hole, Plastic Injector Disk

I am not convinced water pumping/circulating performance will be substantially improved by an air injector disk with multiple injector holes, instead of a simple T-injector.  But it might.

The following is the concept I would build if I wanted to use a plastic air-injector disk in a 4-inch diameter airlift pump (figure below).

- Injector disk would have three (3), 3/8” air holes rather than seven (7) smaller holes – to minimize fouling and calcium deposits (0.688 cfm air-flow per hole).
- Injector disk would be inserted into the air T-Injector rather than the water intake Tee.
- A threaded clean-out cap would be used on the bottom of the air T-injector to allow access to the injector disk holes for cleaning.

(Click figure for full-size image.)