Check Valve or otherwise known as a Demand Valve has an inlet of 3/8" or 9.5mm John Guest and a 1/2" or 12.5mm Barb Tail outlet. The Check Valve should be positioned just behind a standard hand pull, the check valve performs an important job it stops the beer flowing through the standard hand pull and out the dispense tap when there is no demand (pump not being pulled). To allow the beer to flow you need to pull the handle to dispense beer which causes a vacuum and allows the beer to flow into the unit.
This unit has a working pressure of between 0 - 45 PSI with no judder (rattle).
This means, if required and using gas assisted pumps, the gas pumps can be run at beer cellar ring-main pressure (38PSI) without any performance variation across your beer engine range. This will create a great advantage when using 1/2pt pull beer engines which require a higher feed pressure.
If you are going to use this valve to stop siphoning in a none pressurised system in PVC hose you will most probably require the adaptor fitting for the inlet to make this into a barbed tail.