We bought several of these so that we would never again get beer up our gas lines. But they performed poorly. Seemed like gas didn't flow very easily, they were very difficult to remove from the gas posts, and they leak if the gas line is a bit taut. The leaking is what eventually caused us to throw them all into a box and we went back to the old standards.
The design entails a two stage check valve. Each stage is comprised of a spring loaded steel ball that ipresses into an o-ring orifice. Without pressure, the spring holds it closed. Positive pressure from the gas line pushes against the ball and spring allowing gas to enter the keg. When the pressure equalizes, the spring pushes the ball against the o-ring orifice. If the pressure in the keg is higher than the gas line, this pushes the ball even harder into the orifice to keep it closed. This a much better design than the check valves in most gas manifolds. In addition, unlike the check valves in the gas manifolds that I’ve seen, it actually works. I tested it with a keg a Star San. However, in the event that some beer makes its way to the first check valve, it will be harder to clean and sanitize. Be very careful if you decide to disassemble it. Make sure to take notes so that you understand how to reassemble it. I bought 8 and will buy three more in the future to replace all of my standard gas ball connectors.
Not cheap, but replacing a regulator because of backed up fluid is MUCH more expensive! Just get this for every gas-line keg connection and enjoy having one less thing to worry about. It is cheap insurance.
There has been many times when shaking to carbonate, the liquid would flow into the co2 line. This necessitated taking the co2 line apart and PBW and Star Sanning it. RPITA. I also have a small 5lb tank I use to carbonate 1 lt test batches. It too, upon occasion, would back up the gas line. In my 6 product line kegerator, when I connected a new corny keg, unequal pressure between keyg and co2 would cause the same thing. This hopefully would prevent that. So far so good. The 3 star rating is for the 9 kegs in my temp controlled freezer. After I depressurized the kegs and replaced the with this item on the kegs no beer was moved the 14' above to the faucets . 14 psi worked to get a good flow before but the gas wasn't going into the kegs at 14 psi. I gradually increased the gas till i heard in flowing into the kegs, 19 psi was the point that the gas flowed. I let it flow for a while, then reduced it back to 14. We'll see if I don't get enough pressure after I dispense and need to turn it back up. I hope this isn't the case.