Turboed air compressor

Back to the air compressor- assuming you COULD somehow force-feed alot more air into it(maybe using a belt-driven screw-type supercharger unit?) one bad thing that would happen would be that it would probably overheat things. When air is compressed it gets hot. Feel the output line of your "naturally aspirated" compressor while it's running. It'd dang near burn your fingers. Compressing it even more by the "supercharging" setup would make it tons hotter(yeah, "tons hotter" isn't a real specific temperature measurement). So, what if you took an air-to-air intercooler off one of those little turbocharged foriegn cars....maybe some nitrous oxide.....nah....just like in an internal combustion engine- there's no replacement for displacement. If you want more air, best bet is to get a bigger pump. But in the meantime, have fun and keep thinkin'!!!

Odd name you got there :o). In theory your idea would work. But the numbers don't add up to anything meaningful. Force-feeding a compressor like that would be similar to moving a compressor from a higher elevation to a lower elevation. The throughput (in terms of scfm) would increase a little because the volumetric efficiency would be increased. As I recall, the moving of a compressor from NY City (sea level) to Denver, CO (10,000 ft?) decreases the scfm capacity about 20% due to the decreased barometric pressure, all other things being the same. You'd be attempting to do something similar in reverse. It won't be enough to make any significant difference in sandblasting. Even if you could succeed in getting a 20% boost, going from probably 17 cfm to 20 cfm would not make the whole thing worthwhile, IMO. You wouldn't get a 20% boost anyway with a typical squirrel cage fan, as their discharge pressures are usually measured in inches of water, not psi. For reference, the difference in barometric pressure between sea level and 10,000 ft is 4.6 psi. That's over 120 inches of water, which is too much for most squirrel cage fans, I believe. Forget it. Not worth the effort. Interesting thought however.

Rod

what I am suggesting is that you would not get anywhere near a 20% boost in capacity with a typical fan. The fan you mention will likely only produce a few inches of water pressure at best. It doesn't really matter what the flow (cfm) rating is. Whatever that flow is, it will rapidly decrease as the discharge pressure increases. When the maximum pressure is developed (a few inches) the flow will decrease to zero. All you will have gained is to decrease the inlet losses to your compressor and help, a little, in feeding the first stage cylinder. That will increase the volumetric efficiency a little bit but I suspect any capacity increase will not be noticeable without some precise, calibrated measurements.

As far as feeding the inlet of your two stage unit with another compressor, you may even wind up in a worse condition with the extra "help". Running compressors in series is not unlike multiple stages in a single compressor. What goes in the inlet to the first stage, comes out the outlet of the last stage, albeit at a higher pressure. The capacity of a multistage machine is determined by the first stage only. That being the case, the quantity of air that goes in the inlet of your "helper" compressor is going to determine the volume of air coming out the outlet to your "helped" compressor. It may not be "helped" at all, at least as far as capacity is concerned. It could be starved instead.

In any event, there is no such thing as a free lunch. It takes power to compress air. Even if by some reason, you could significantly increase the throughput of your two stage unit, you would, in all probablility, overload your existing drive motor, at least at the higher end of the discharge pressure. In fact, with marginally rated motors, just feeding a compressor very cold air can overload the motor due to the denser air at the lower temperature. Other than minor tinkering with increasing the volumetric efficiency (such as porting the inlet passages and removing the inlet filter), about the only way to increase the capacity of an existing unit is to increase the speed. That would also require a larger drive motor. If you really need significantly more capacity, the best way to get it is simply with a bigger compressor that has greater displacement and a higher HP motor. A fact of life, I am afraid.

However, good luck with your experiments. I hope you proove me incorrect.

Then again, it's a good way to while away a winter afternoon, so why not?