After owning the Harbor freight sand blast cabinet for 5 years, my daughter has motivated me to put it together with decent parts. So, I picked up the bottom feed metering valve for the sand feed. The simple one with a ****** on it for an air bleed (I bought mine on Ebay). I can't figure out the adjustment on it. No matter how I had the set screw threaded in didn't seem to effect the feed or lack of feed. I could try to start blasting, some sand come out, hold my hand against the nozzle and burp air thru the line, then back to blasting.