Air System Check Valve

[Maycinc@cs.com]

I'm thinking of putting a couple of check valves in the air lines.  One right 
after the compressor to keep pressure off of it and one after the oiler so I 
can refill it without loosing all the air in the system.
The question is: What kind of check valve do I use and where can I find one?
Marvin
#1343