I checked mine today. I didn't get any fuel from the return line when I took it off. Then I pulled off the 90deg ell (which had no signs of fuel in it) and then pulled out the check valve. It looks like it's glass or something. I didn't see any particles in it. I tried to blow through it and could barely get any air through it. Tried both ways, obviously with one way not being able to get air through it.
... Ok that was my video on YOUTUBE .... hence the atlashayco ID ...
Anyhow. Yes the check valve. That does seem to be a piece glass, but what you didn't probably notice is the spring on the side further from the IP when mounted.
The valve's spring is set for pressure, but if there is "gunk" layed into the spring coils it does NOT retract there for not allowing fuel to pass into the return system.
I have figured in my experiences now that if the return system does not have fuel fed to it the IP "overloads" and gives you white smoke. WORSE YET this, in my mind, would harm the IP - one of the pumps in the IP - THERE IS MORE THAN ONE LEVEL OF PRESSURE IN THE IP.
I have now replaced my IP, Injectors, forward and return lines, a fusible link, tank seal for the sender, Fuel water seperator, returns, seals in the forward connections, and lets see what else .... nothing else other than filters comes to mind now.
NO MORE WHITE SMOKE.
OK you may be able to clean the CHECK VALVE and reach good results. In my case there was a constant build up of black specks. I dont know if I was having algae or IP flex ring. PROBABLY some of both, but the IP was original and when I recieved the new one - hand turning both showed me differences in operation (sound, smoothness), and the shaft was a bit loose on the old one.
TRY CLEANING THE CHECK VALVE with a small pick or two, compressed air, and the tapping method. I had pretty good results when "flicking" the spring that you can barely make out!