I just bought one a couple weeks ago, also a noob to sandblasting. I haven't tried walnut shell; I've been using aluminum oxide. With those caveats, here is what I've learned so far:
1.) The instructions it came with are wrong. They tell you to open the sand valve (on the bottom of the pot) all the way and regulate mix with the valve on the air bypass hose (I forget what they call it). Instead you need to regulate mix with the sand valve on the bottom, and open the bypass valve all the way or nearly all the way. See this youtube video:
2.) The nozzles that come with it are too small and wear out too quickly. I plan to get a new 'gun' for it that will accept heavier duty nozzles
3.) You will need a moisture trap. I added a pressure regulator with built-in moisture trap followed by a second trap. I had to drain the first one every 5 minutes or so as it would fill up.
4.) I plumbed two compressors to it for a combined 10 cfm. This was just enough to run it almost continuously at 40 psi, which is the minimum usable pressure. I just bought a 240v compressor to add to the mix for 22 total cfm running all three in parallel. I will look at the charts online when I buy the new gun and nozzles to see what size nozzle this will support at ~90 psi. I'm thinking probably an 1/8th inch nozzle based on one chart I saw, but I need to dig further. There is probably a minimum nozzle size you'll need to run walnut shell.
Hope this helps!
