This inline wort aerator is intended for low pressure supply situations. This device also relies on even lower pressures on the downstream side of the aerator. The low pressure on the downstream side is assured by the 10 inch length of hose lower than the body of the aerater. If not enough air is entering the wort during usage, the supply side flow will need to be restricted further.
I used this aerater on my last batch when I filled my primary. By the time the primary was full I had a good 2 inches of foam on top of the wort. I didn't even use the 10" piece of hose downstream of the aerator. Needless to say that this was the first batch I ever needed a blowoff tube for. I had a 5 gal batch in a 6.5 gal glass carboy and the foam went up clogged the airlock, blew it off, and proceded to flow down the outside of the carboy. Made a mess. I used exactly the same recipe and process as a previous batch just used the aerater instead of shaking the carboy. Still need to taste the beer.
Building your aerator
Use a piece of 1/4" soft copper tubing and cut it to a length of 4-5 inches. Using a tubing cutter that works by a non powered cutting wheel and rollers, compress rings into the tubing to act as supply side flow restrictors. Work the tubing cutter as if you were going to cut through the tubing, but don't. Next drill through the tubing with a 1/16 inch drill bit twice with the direction changed by 90 degrees. This should produce 4 1/16 inch holes. Now clean up the copper tube and attach the vinyl tubing to each end and try it out.
If you wish me to produce one for you, just email me and we can work out the details.