Still Thrashing About A Compressor

[OK-944]

OK…so I’m down to two air compressor configurations for soda blasting. One is a 20 gallon, vertical unit - oil free, which maxes out at 175psi, and puts out 4CFM’s at 90psi. The second is a 10 gallon horizontal unit, needs oil, which maxes out at 125psi, but puts out 5.1CFM’s at 90psi.

While most blast units for soda specify “at least 7CFM at 90psi,” I’m coming to understand that this assumes a continuous output. But, I absolutely do not need continuous output! Short pulses are fine, (and I can stop to wait to let things cool off) and thus, from what I can gather from other people’s experiences, either one of the above units should be fine.

I plan to use a gravity fed, hopper incorporated, handheld blaster - which from what I can tell makes sense for the short blasts I’ll be using, also that I can easily shake the blaster if and when it gets clogged.

The blaster I’m considering is designed to operate at a maximum pressure of 125psi - which means that the 175psi, 20 gallon compressor, assuming good regulator adjustment, should give me a bit more time to blast between charges, while the 125psi, 10 gallon compressor will fall off more quickly. But…what about the CFM ratings, which are better (5.1CFM at 90psi) for the 10 gallon, 125psi unit than the 4CFM (at 90psi) for the 20 gallon, 175psi unit?

I just need a bit more clarity on this before I choose a compressor, so if anyone can help clear things up - that would be great!

[91cab]

Nice to think you will stop every once in a while. Soda blasting is like using an eraser to erase a sheet of paper covered solid with pencil markings. It is a very slow and tedious process. You might be able to do a small bracket in one shot. Not using a cabinet will get expensive VERY quickly. If I did my intake manifold with glass and no cabinet it would cost $20 or $30 in materials. To do an intake manifold with the compressors you are mentioning would take hours. Running these "home" compressors continuously will overheat and burn them out fairly quickly (already burnt one out). So you can blast for 2 minutes and then wait for 30 minutes for the unit to cool down.

[OK-944]

So what if, on finding that the 4cfm unit is not enough - I purchase another one and gang them together?

[91cab]

I do not know if you can "gang" them together. You can however use a second one as a reserve storage tank. Maybe you can find a compressor with a burnt motor for $25. When my 33 gal burnt out I got a 30 gal and hooked it up to the 33 gal tank for a total of 66 gal storage. With this storage I can blast as long as I dare to heat up the compressor. Oil lubed compressors are more durable then the teflon compressors. Get the biggest, highest output compressor you can. Air tools use a lot of air. If you use a blast cabinet you will also need a vacuum so you can see. If you do not use a cabinet use a large plastic lined box with clear plastic on top so you can see and recover the media. I did this for parts too big to fit in the cabinet.

[91cab]

To find the volume of a tank devide the gallons by 7.48. On your 10 gallon tank it is 1.34 cf. 14.7psi is one atmosphere so 125 psi is about 8.5. This might get you 2 minutes. However the ratings on the compressor are WRONG. I think my comp says it is 6hp. Not physically possible, it runs off 120 and a 15 amp breaker. It is probably 1hp. The other numbers are "optimistic" also. I would say you have closer to 1 minute the 2 of run time.

[jjeffries]

Ive been following along with your threads.
Buy the biggest one you can.... with the highest output pump.
Years ago i did the extra-tank thing (pulled an air brake tank of a dump truck), doubling the size of my air storage, but it yielded no meaningful help to high air consumption activities (sanding, blasting, etc). The compressor was a 1.5HP, 12 gallon Craftsman, which ultimately was effective for little more than blow gun, tire pressure setting, etc.
Obviously I don't know what money, space or electrical service you have available, but I believe anything less than the following will disappoint: 5HP, 240V, twin cylinder, 60 or 80 gallon tank. Good news: Craigslist will often yield such units in the $500 range. If they have been maintained, they last pretty much forever. John