I recently purchased a new sandblast cabinet for my workshop. Finally I’ll be able to strip paint and remove rust from small parts. I have never used a cabinet before and I am hoping that my current air compressor will be powerful enough to run the cabinet. The cabinet and gun documentation recommend a compressor that can provide 7-14 CFM at 90psi, with the higher number being much more desirable. My compressor sits near the lower end of the scale, providing A modest 9 CFM at 90 psi.
I am hoping that it will be enough, but have started looking at replacement compressors so I can get an idea of what a new one will cost. What I am finding is if you need a compressor capable of more than 11 CFM it is going to be expensive! But I am really not sure if what is more important in determining CFM numbers. Its it more important to have a larger tank or a higher horsepower compressor motor? If it is the former, are tanks available that I can move my current motor over to? Or if its the motor, would it be better to use my current 25 gal tank and replace the motor?
For a full replacement the best compromise I have found is a $600 unit that provides 12.5 CFM. Am I worried too much about the CFM numbers? Will my current 9 CFM do the job, just slower? I am finding the wonderful world of compressors very confusing.
If it makes any difference I have purchased a Rapid Air System that lets me put pipe in my walks and had two outlets, one for the cabinet and one for a 50’ reel. There is a water filter where the compressor connects to three pipe system and another at the connection point for the blast cabinet. Both the cabinet and reel have their own pressure regulator. Also, the unit isn’t being used in a shop and won’t be use every day.
Your small cabinet sand blast system will work the best with your air pressure at 90 psi. Your compressor will supply adequate supply for short cycles of cleaning, and you say you are cleaning small parts and not everyday, well I would just not get too pumped up and just give it a try and if you are not satisfied then look to a larger output compressor. Putting a larger capacity receiver(air tank) will give you an increase in flow time but will also result in your compressor running much longer to bring receiver up to cut out pressure. If you are satisfied with your compressor so far, leave it alone.
DO NOT ADD PIPING! Air (or any fluid) moving through any tube will experience “friction loss” - the longer the hose/pipe, the more friction, meaning less pressure and/or flow rate.
Same with filters and regulators - unless absolutely necessary, they reduce efficiency of your compressor.
Since you are at the low end of usability, don’t add to the problem - get the compressor as close to the cabinet as possible, and use no more hose than absolutely necessary.
The motor/tank on a compressor is analogous to the burner and tank on a water heater - if you mix a small motor with a large tank, you may get a longer spray burst, but it will take longer to recover.
The plus side is that compressors (WATCH THE VOLTAGE REQUIREMENTS) is that they are built to last pretty much forever - if it has a cast-iron compressor unit and a motor made by a motor making company (the data plated on the motor should list a company different than the name on the compressor) , they can be rebuilt (about every 50 years of commercial use) forever.
IOW: nothing wrong with used. I have a tiny Campbell-Hausfeld from the 1980’s which was used commercially until 1996 - it takes a bit longer to get there, but a change of seals would put it back into new condition.
Too late at this point, the air delivery system is already in the walls and necessary. The system I used is this one http://rapidairproducts.com/rapidair.asp My workshop is 30’ long, so moving the compressor around would be quite a chore. The water filters are really only a concern with the cabinet at this point as I want to be sure to keep the abrasive material as dry as possible to avoid clumping. The regulators are at the end point of each “line”, so they shouldn’t have a multiplying effect in each other. I thought about only using a single at the compressor, but the convenience of being able to adjust pressure at the tool being used should be worth any small sacrifice in performance. My current compressor has done a great job in the past keeping up with the demands of ratchets, impact drivers and sanders so perhaps it will run the cabinet without issue. I started reading the blast cabinet manual and guess I got my head wrapped around the specs. Only way to find out if I have enough CFM is to try it out.
From what I am gathering, the lower CFM will translate into longer wait times for pressure and perhaps a reduction in stripping power the media. It doesn’t look like it will make the cabinet unusable, but rather increase the time it takes to finish a project. Since I am not using this in a professional setting, the longer completion times might not justify the expense of a new compressor. Hell, the cabinet is rated between 7&14 CFM so it should work.
I am still not clear however on what plays a greater factor in determining usable CFM, tank size or compressor HP. I am leaning towards tank size, figuring the larger the tank the more volume it can provide. I am thinking the HP rating would be more relevant to time it takes to fill the tank and not so much factoring into CFM figures. Thanks for the information.
You didn’t mention it in your OP, but if yours isn’t already first and foremost in terms of upgrading get a compressor that has a 220V motor (dryer/electric range plug). They cost more initially but actually use about half the electricity to do the same amount of work, and will be mated to an appropriately sized compressor. Even if you’ll need to run a new electrical line to it (the motor’s cord will be very short) it’s worth it. The next big step compressor wise is going from a single to a 2-stage model.
Easiest thing to do is use the setup you have now for a while and find out if it will keep up with the amount of work you need to do. You’ll find out pretty quickly if the compressor is running nearly constantly and/or if you’re spending too much time having to stop and wait for the pressure to build back up.
I have a cabinet that I run with an 11 CFM compressor sitting on a 60-gallon tank. It’s barely adequate. The tank will maintain supply pressure (and therefore CFM) long enough to get me through brief blasting jobs, but if I’m blasting for more than maybe 5 minutes, the tank pressure will fall off, the air pump will start running, and now I’m engaged in a battle: at the time the pump starts running, my gun’s CFM exceeds the pump’s CFM, and the tank pressure will continue to fall off until my gun’s CFM falls to where it matches that of the pump. For me, that happens at about 70 psi. Nozzle velocity falls off, which means fewer particles of sand per second, and they’re also moving more slowly, so I get a much reduced blasting efficacy.
TL;DR:
for short jobs, a big tank will see you through. For longer jobs, you need a pump with high CFM, ideally one that exceeds the CFM of the gun.
If you’re concerned about clumping of your sand (and you should be), you’ll need to dry the air before it reaches the gun. Start with a coalescing filter to remove the already-condensed liquid droplets. I use this one; After that, you’ve still got air that’s at something close to 100% relative humidity, and when it leaves the gun nozzle, it’ll expand and cool, causing that remaining water vapor to condense. So you’ll want a desiccant air dryer; I use item #5163K21 from McMaster, but you might find other options elsewhere.
In simple terms, your tank(receiver) is a storage unit and is not needed if you have a compressor with a CFM displacement high enough for the work needed to be done. Take a construction sight with jack hammers used, there will be a screw compressor screaming away constantly with a 2,3,4,…8> hundred CFM output. Your tank gives you a supply to use until you need to rebuild, it also performs a very important service and that is to cool the compressed air. Hot air holds way more water than cold air some contaminants. The tank needs the drain valve operated often to get rid of moisture and contaminants often and an automatic drain valve is commonly used.