mounting check valve...

i have a 3/8" SMC check valve on a compressor leader hose that will work most of the time, but sometimes let air come back through the compressor. does it matter if it is lying horizontal (which mine is) or vertical? does one way keep water from building up inside it and make it not work? could that be why mine fails occasionally?

i dont think it matters. its possible you have a bad check valve.