Sandblasting: Pressure Pot Set Up

I've sandblasted since 1982. In the beginning I build a reclaiming box and did syphon blasting. After the internet I learned about pressure pots. I got a pressure pot in 2005. I have used it with okay results. (It will sometimes have flow issues.) I have two desiccant filters (to remove moisture in the line) between the compressor (Sears 150 PSI, 60 Gal, 7HP upright) and my pressure pot (Harbor Freight special). I don't know what has happened. I've physically emptied the pot to check for debris (when I recycle the aluminum oxide I screen it as I refill the pot. I am careful to not get foreign debris in the pot.) I've taken apart the lines to check for obstructions and found a few tiny bits near the tip. I have several ball valves that I've checked and all seem to work fine. But I have no pressure to speak of nor sand coming out. I've read on this forum and the Pro Contractor's form about even pressure. I don't quite understand that.

Generally I have my compressor set high and my pressure pot set lower. I have worked under the impression that a pressure pot needs less pressure to work than a syphon. When I did syphon blasting I used about 40-60 psi. With the pot about 15. Now I have it set higher and see poor results and it is not working. This is driving me nuts. I have jobs that hang in the balance and I need this to work. (My last job I had to borrow a friends set up.) What have I set up wrong?

Does anyone have PSI settings for using a pressure pot?
Pressure in the compressor:
Pressure in the pressure pot:
Which valves are opened:
Which valves are partially opened:

I need this tool to work well. It is how I earn my money. I am an artist and this needs to deliver pressure and media when required. I have a large job coming up this week and I need this all to come together. ANY help will earn you my blessings and prayers. Thank you.