Myths and Questions
Since you've read this thread, you can see that I was not overly impressed with the venturi units, whether past or your company's unit shown in Louisville at Brad Packard's booth. Your silencing of the unit will certainly be an improvement, but several issues seem to persist; namely CFM and compressor use.
Originally, "vacuum" chucking started with people using shop-vacs with their very high CFM capacity and air velocity ratings to suck the pieces onto the bell and hold even porous woods. People found, however, that running those vacs with the hoses "blocked" soon overheated, then burned out, the non-bypass motors, so enter, stage right, real vacuum pumps.
Outside of the industrial and automotive areas, it seems as though the venturi systems were widely used in the veneering context because they could evacuate a perfectly sealed environment like the heavy poly bags used. Users coupled them with a reservoir tank of several gallons' capacity and ran a small compressor only intermittently to maintain a set pressure of between 10 and 15" of Hg. They were great for applying veneer to curved surfaces, and erased the need to worry about CFM issues because the bags and fittings were all very well sealed against leaks; suck & hold was the short order of the day. You state your unit will work well with a 2 CFM compressor with a 65 PSI feed. Most people don't understand that as PSI goes up, the relative CFM produced actually goes down, but a venturi is the perfect illustration of that situation, as are HVLP spray systems. However, as I understand it, your venturi, while capable of pulling an improved 20" vacuum, cannot "pull" more CFMs than the compressor is delivering, and unless it's 100% efficient, would actually be pulling less than the compressor's CFM output. But a simple vacuum rating is not enough. Again as I understand it, it's the CFM rating that is vital to a vacuum chuck's ability to deal with porous woods and imperfect seals throughout the system, even with the use of a 3-piece vacuum adaptor. Most good small vacuum pumps [Gast, Robinair, DeVilbiss, Thomas] will pull in the 5-6 CFM range which works well for woodturners because they have enough flow capacity to compensate for small leaks, and naturally porous woods or workpieces with unseen micro cracks. So, how much CFM does your system generate with a small shop 2-4 CFM compressor like most here would have, and how does it compensate for "leaky" wood?
Next issue is the cost and noise of running an air compressor to operate a venturi as opposed to running a regular vacuum pump system. The smaller vacuum pumps (actually a compressor using the intake) in use by turners are usually in the 1/3 to 3/4hp motor range, and are rather quiet, especially when run with out-flow filters or mufflers. There have been a number of threads here and elsewhere regarding people seeking to soundproof their air compressors because of the very high noise levels they produce. Seems nobody wants to spend $20K for a silent compressor. People also don't consider the cost to run those 1.5 to 2 hp motors which is much more than running a 1/2hp vacuum pump. Thus far, I've not seen anything about your venturi generator that addresses the compressor noise and net cost of operation when compared with a vacuum pump set up, so other than the initial cost and 1 cu. ft. of space needed for the pump, what advantage does your system have over a vacuum pump set up?
Now, if I've stated something you feel is a myth, feel free to correct me. Accurate and complete information is the only type that has any value, and I certainly don't want to mislead anyone, let alone perpetuate myths.
