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dewat
04-10-2009, 08:09 PM
I'll be doing a lot of sand blasting soon, my compressor is a 33gal single stage I bought from Sears, it works well but it's noisy and of course can't keep up with the amount of blasting I do, I usually run at 90psi. This would be a little extra work, but I was thinking I'd mount a 5gal bucket above the cabinet and let it gravity feed . So the question is, would the air volume/pressure use be reduced enough to justify this.

TIA

Jim

brian Rupnow
04-10-2009, 08:13 PM
I don't think you will see any difference in pressure/flow requirements. Maybe a little better sand delivery, but no major difference.

bob ward
04-10-2009, 09:23 PM
You are thinking of an overhead gravity sand feed rather than the sand being picked up by the venturi effect?

My thought is that while the energy used to pick up the sand by venturi is not 'free' energy, it is insignificant in the overall air compressor energy being expended in your sand blasting activities.

But as Brian says, the overhead pot may give you better sand delivery.

chipmaker4130
04-10-2009, 09:24 PM
What type of blaster do you have? Siphon feed or pressure feed? You don't mention the hp of your compressor, but with a 33 gal tank I suspect it is less than 3hp. Probably much less if so-called 'running hp' (true hp) is considered. Using a 1/8" nozzle at 90 psi, you'll likely get less than 1 minute of work done before the pressure drops significantly. You need at minimum a 'true' 5hp to run 90psi @ 1/8" and 7.5hp would be ideal.

Gordon

ClintonH
04-10-2009, 09:36 PM
If you don't have the CFM you just don't have it. Mounting a gravity feed wont make any difference as you'll have to add more air to compensate for more sand.

im#2
04-10-2009, 10:25 PM
Jim: I have a home made cabinate with a tapered bottom, and the feed is ok but the 60 gal. 5 hp. compresser just wont quite keep up. So I get to take breaks, some more often then I want to! Think you will be taking more breaks than I have to!

dewat
04-11-2009, 03:34 AM
Thanks guys, I guess I'll have to come up with some other way to beat the system. :D

pgp001
04-11-2009, 05:48 AM
If you dont have a big enough compressor, the only other "half way house" solution is to have a large air receiver in the system to let you blast for longer.

Phil

dewat
04-11-2009, 05:31 PM
Thanks Phil, I'll check into that.

pgp001
04-11-2009, 06:44 PM
I have assumed you are using a suction feed gun by the way.

If the gun is anything like the ones we make, it will have an 'air jet' where the air enters the body.
It may be possible to reduce the size of this a bit so it passes less volume of air at a given pressure. This will make it less powerful but allow you to blast for longer if your air supply is limited.

Just another thought, 90 PSI sounds way too high for most blasting applications, 70 to 80 is usually the max.
If you blast at a very high pressure the speed of work will increase, but you will break down the blast media very quickly and soon lose the advantage.

I design machines for Guyson's by the way.

Phil

radkins
04-11-2009, 07:11 PM
If you dont have a big enough compressor, the only other "half way house" solution is to have a large air receiver in the system to let you blast for longer.Phil


That usually is not worth the effort either because it is a trade off. Sure it will let you blast a bit longer but then the recovery time is proportionally longer too.

For example if you can blast for 1 minute then have to wait 4 minutes for the pressure to recover with the tank you have that would be 6 cycles of 5 minutes each in a 30 minute work period so you will have been able to blast for 6 minutes but had to wait for 24.

If you double the tank capacity you should be able to now blast for 2 minutes but then would have to wait for 8 minutes for the recovery period which would be 3 cycles of 10 minutes each during the same 30 minute work period.

Again you will have worked for the same 6 minutes and waited the same 24 minutes on recovery time so you really don't gain anything. Adding extra tank capacity is a common attempt to increase a compressor's performance but unfortunately it is usually an exercise in futility. Just like ClintonH said if you don't have the CFM then you just don't have it and adding tank capacity will not change that. Of course the numbers I used are just picked for illustration purposes and your compressor would almost certainly have different run/recovery times but the principle is the same and no matter how much tank capacity you add it will not gain any working time.

dewat
04-11-2009, 07:15 PM
Thanks Phil, I'll experiment with the jet size, the blasting I'll be doing is for parkerizing prep. I usually acid etch but blasting gives it a better finish, so more experimenting all around is called for. Come to think of it I'm not sure why I've been using 90psi, something I saw in the instructions ? I'm not sure LOL. It's a HF unit. Yeah, that's the ticket...... I'll blame it on Harbor Freight :D

Thanks
Jim