Sandblast cabinet pressure
- Thread starter albaran
- Start date
John in OH
Well-known member
Not knowing the specifics of your installation, I would have to say, "Yeah, that may be normal".
As you know, as soon as air starts flowing in a pipe or air line the frictional pressure drop in the piping will eat up a lot of your working pressure between compressor and nozzle. Also, consider that when you pull the trigger you are essentially opening a 1/8" to 1/4" hole in you air line with little restriction. The air rushes out and down goes your pressure. Lastly, a 6hp compressor (I assume it's single stage since you say it is an old CH machine) will have to work pretty hard to maintain any decent sandblasting pressure. And sandblasting uses a LOT of air.
As you know, as soon as air starts flowing in a pipe or air line the frictional pressure drop in the piping will eat up a lot of your working pressure between compressor and nozzle. Also, consider that when you pull the trigger you are essentially opening a 1/8" to 1/4" hole in you air line with little restriction. The air rushes out and down goes your pressure. Lastly, a 6hp compressor (I assume it's single stage since you say it is an old CH machine) will have to work pretty hard to maintain any decent sandblasting pressure. And sandblasting uses a LOT of air.
FredWanaker
Well-known member
I have two 5 hp compressors in parallel and it takes that to do a decent diy job. We used a big 3 phase industrial compressor in the shop for blast cabinet work. What usually happens is that the regulator needs to be turned all the way in to get that 70 - 90 psi and then the pressure falls off to 45 - 50 psi after a few minutes and you have to take a 5 minute break before it recovers. Better have a good fan blowing air on that compressor too because the built in fan on the wheel won't be able to keep up with the heat from 100% use.
Jswain
Well-known member
If you're choking everything running it through those 1/4" lines that is likely your problem. Post pictures of your entire setup, including the entire compressor and lines from it to the blast cabinet.
3/8" is ok for blasting under 25ft but 1/2" would be better. Since you're only starting with 90psi you will want the least amount of pressure drop possible in your setup.
3/8" is ok for blasting under 25ft but 1/2" would be better. Since you're only starting with 90psi you will want the least amount of pressure drop possible in your setup.
firebirdparts
Well-known member
Pressure drop will happen, yes. You can change the system (bigger lines) to make it do what you want.
metalmagpie
Well-known member
Do you understand electricity? In a circuit, if current flows through a resistor there is a voltage drop across the resistor. Well, the mechanical analog with air is that pressure is like voltage, flow is like current, and resistance can be small pipes or anything. With no air flowing your pressure is 100 psig. If when you start the air flowing the pressure drops to 50 psi then that always means there is resistance between the tank and the gauge.
For air, resistance can be hose size or pipe size or other.
You should be able to do very light sandblasting with an actual 6hp 2-stage air pump. However, for most of the last 40 years compressors have been sold with enormously inflated horsepower ratings. It used to be common for a compressor to claim 5 horsepower but the motor be rated for max current of 12 amps at 240 volts AC. This means it's really a 2 hp motor. Campbell Hausfeld was one of the chief perpetrators of this hoaxing. So it's possible your 6hp compressor may not be what you think it is. Look at the current rating on the motor and it will tell all.
metalmagpie
For air, resistance can be hose size or pipe size or other.
You should be able to do very light sandblasting with an actual 6hp 2-stage air pump. However, for most of the last 40 years compressors have been sold with enormously inflated horsepower ratings. It used to be common for a compressor to claim 5 horsepower but the motor be rated for max current of 12 amps at 240 volts AC. This means it's really a 2 hp motor. Campbell Hausfeld was one of the chief perpetrators of this hoaxing. So it's possible your 6hp compressor may not be what you think it is. Look at the current rating on the motor and it will tell all.
metalmagpie
FredWanaker
Well-known member
what metal magpie said is true. My 2 compressors are "5 1/2" hp each but if one does the actual calculations they are about 2 - 2 1/2 hp each. Even with 2 of these with the tanks in parallel, they run about 75% of the time when I am glass beading. One thing that will really help is get an good industrial pickup. The ones that come with the typical small blast cabinet are junk.
Your line going to the sandblast cabinet are too small. My bet is you have a 1/4" or maybe a 3/8" hose. Is it that yellow coiled poly air hose in the background in one of your pictures? Definately too small! What size is the line on the wall from the tank to the yellow hose?
I would run 1/2" all the way from the compressor to the sand blaster.
I have done a lot of sandblasting with a 3HP unit, but it was too small. 5HP would be a lot better, but you will need to run a smaller nozzle on the blaster.
My guess is his 6HP compresser is really just 3HP. One of those "liar" HP ratings!
To the OP, what is the voltage and amp rating on you compressor motor? My bet is 240 volt and around 15 amps.
Success! Thanks to all of you for your input. I replaced the 3/8 line with a shorter one from the compressor to the blaster and changed over the quick diconnects to ones that allow a large volume of air to flow through. As you can see from the picture, the nozzle pressure is now about 110 and the pressure with a pressed trigger is about 95.
Attachments
CraigStu
Well-known member
Wow, that worked out just fine for little $ spent. I was going to ask why you only have 90# but that is a moot point now. Good job.
Tinkering_hobbyist
Member
- Joined
- Feb 10, 2022
- Messages
- 5
Had a quick question little more to do with using a smaller compressor. I have an older compressor about 5ish cfm at 90psi. I realize it’s under powered but I’m doing small jobs. I can hook up an extra air tank as well but I’m just looking to blast tools. Biggest tool is a Ridgid 2a pipe cutter. Most of the blasting will honestly be like the rollers, or the inside of the parts as I can get the outside with my bench grinder easily. I just would like the ability to get the smaller detailed stuff. So even if it’s a smaller compressor, I add in an additional tank, can j get away with really small projects for cleaning tools with a #2 or 3 nozzle? I also have an airbrush blaster, I was thinking of trying that as well as I’m not blasting sheet metal or massive surface area. Sorry to hijack but thank you very much.