What is a Valve Check (air suspension system)

I have air-runner for my y33 and my airrunner system does not have a valve check., 

everyone talks about having a "valve check".

what is the purpose of a valve check ?

you dont need it, you have manual valves. its used for the electric valves. its used so the air pretty much wont get pushed back to the elec valves and leak through it. its like a door that opens only one way

You should run check valves anyway.  I've driven a bagged vehicle daily for over 5 years.  I would run a check valve at the tank and check valves before each dump valve.  That way if you lose pressure your car won't just layout by itself.

^^^^he has manual valves. it wont matter. even if he emptied out his tank full of air and his bags top off. the bags wont deflate. its been done to my car at AF while swaping out my old tank

I would put a check valve between your compressor and tank, some compressors have built in check valves but in my own experiences, Viair's inline check valves failed me 3x's.