Oil catch can and check valves

[OffTheWall503]

I just recently purchased a Mishimoto oil catch can and I've been doing research and noticing people add check valves to the front silicone line. Is it a necessity? What is the benefit and if it helps, why haven't manufacturers started including these in their kits?

 

[KKaWing]

To keep the catch can from getting pressurized from boost. Most cans should be able to handle it but it's more of a safeguard to keep stuff from leaking out the can and such.

 

[MOFiST]

Another reason to use a check valve is for the can that Damond Motorsports uses which features crank case VTA when on boost.
http://www.fiestastforum.com/forum/threads/6374-Damond-Motorsports-Fiesta-ST-Oil-Catch-Can-kits?p=113216&viewfull=1#post113216
This alleviates high crank case pressures when on boost and this is can I'd buy if I was buying another.
I'm actually considering upgrading to it although I'd need to keep my custom pipes for my RHD 3dr.
It's not needed but it is better to have. Even if just to prevent boost pressure on the can.
The seals on your can if no check valve need to be perfect or else it could be a source for a boost leak etc.