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Topic Review (Newest First)
08-25-2005 08:31 AM
oldred A large nozzle will break you up in sand costs as you have already found out. Sounds like you have a water problem and the best way to address this is to work on cooling the air first since wringing moisture from hot air is a major problem. The air should be run through a heat exchanger or some other means of cooling before the water separator and then another water separator located on the blaster itself should do the job. Other than that try to blast when humidity is low since the water produced is what is contained in the air being compressed.
08-25-2005 07:54 AM
66GMC
Damp air or damp Sand?

Quote:
Originally Posted by oldred
dry air, which as you very well know, is a must for sandblasters.
Yup, I can vouch for that!

I was complaining that my borrowed blaster was consuming a LOT of sand when I went in to pick up ANOTHER 6 bags. The fellow at the counter asked what kind of equipment, and what did the nozzle look like? I told him that it was an old diesel-powered IR compressor on wheels with a 100lb tank (see my project journal), and the nozzle had a hole in it the size of a pencil... which he says is a bad thing ... worn out ... then showed and sold me a new one.

I put it on and tried it. It would work great (obviously using less sand) for about 5 mins, but then the sand stopped coming. The nozzle was obviously spraying water mist as well, so I took the nozzle right off, blew out the lines, and drained the traps. Then it would work fine again for another 5 minutes, and I'd have to repeat the whole process!

In frustration I put the old nozzle back on and finished off that bag. The larger nozzle opening must have been keeping the volume of air up and the lines clear? Maybe I had a bag of damp sand? I'll have to try again this weekend with a fresh bag of sand.

Any comments? (I'm a sandblasting newbie)

Don
08-25-2005 07:17 AM
oldred Bob, You also have to wait longer on the recharge cycle so if you use your blaster for more than one cycle you don't gain any time although I am sure you already know that. Sometimes it may be more convenient to have longer use/recharge times than shorter more frequent cycles but over any continuous period that requires more than one cycle the use/wait times will add up to the same amount regardless of tank size. However as I pointed out earlier you need to keep an eye on compressor pump temperature because of those long recharge cycles.(I am assuming you added those tanks and you are not using a large industrial size compressor?) One advantage you do have with those multiple tanks is the fact that they give the air a chance to cool and make really good water traps and dry air, which as you very well know, is a must for sandblasters.
08-25-2005 04:59 AM
jcclark
Quote:
Originally Posted by Festive57
Out of curiosity,is there some way to determine what cfm your compressor has at 90psi
Thanks,
Bill
There are formulas using tank size and time it takes to pump to a certain pressure. I think my Eaton is about 17 cfm at 90, the company checks its
performance by checking the pump up time to 150 psi. On my 60 gallon
it takes 5 minutes, on a 80 gallon it takes 6 minutes. If you time yours
you could probably compare to others and get a good idea of the size.
I think Bondoking has a 12 to 14 cfm at 90 psi and we timed his at
8 minutes (I think?) If you post your time maybe someone here can
compare.
08-24-2005 09:05 PM
baddbob Common sense, tank size equals storage size, compressor cfm equals running capablity, pressure cutoff can effect stored volume. 175 psi is common for many compressors sold today. Tanks are rated and usually stamped or tagged.

Having three tanks allows me to sandblast three times longer before the compressor kicks on because the storage has been increased. My compressor doesn't supply enough cfm to support steady full pressure blasting but the storage size increase allows me to blast at full pressure for a longer period of time. Basic example.
08-24-2005 08:39 PM
Festive57 Out of curiosity,is there some way to determine what cfm your compressor has at 90psi ? I mean some way other than some expensive air flow tool? I bought my compressor some years ago and have long since lost all my literature.

Thanks,
Bill
08-24-2005 02:01 PM
oldred Rick, That is EXACTLY what I have been saying. I did not mean those guys at the mine were doing the right thing and I have warned repeatedly about the folly of overpressure but some people just will not listen. I see it all the time, someone will come into the shop and say "my compressor will not keep up with my 1" drive impact how much will you charge for a bigger TANK!" or "do you have a regulator that will allow me to run 200 lbs" . It seems too many people want to believe that more STORAGE translates into more compressor CFM and I have trouble making them understand that storage will not make up for insufficient pump CFM. In this case we were discussing extra tank pressure being used as extra tank volume not extra pressure at the tool and my point is that TANK volume no matter how it is obtained is not going to make up for a compressor that is too small, at least not after running more than one recharge cycle. If the pump CFM is low it is a small compressor and will perform like a small compressor even if you do up the pressure or add extra tanks. As for running 150 PSI on large tools like 1" drive impacts that much pressure will make a difference just not as much as most want to believe but running that high above the recommended pressure is common practice here,right or wrong, has been for years and I assume it will remain so. The efficiency drops off dramatically above a tool's designed operating pressure so a huge increase in pressure only amounts to a small increase in performance but this is often enough to make it worth it to some so as I said they will continue to do this. Also 175 PSI cut-off pressure is commonly found,from the factory, on two stage compressors with 60-80 gal tanks and 15-20 CFM range that are sold for small shops although some are less than that and I think what started this discussion was if raising the designed cut-off pressure would be beneficial or not and I think that at this point everyone understands that volume and pressure are two different things but getting more VOLUME to run tools was the original subject not more pressure at the tool. I don't see where anyone even suguested running more pressure at the tool and the examples I gave were to show how common it is for some to misunderstand the problem and the extremes they will go to.
08-24-2005 01:22 PM
jcclark I thought that too, all the tools I've seen said 90 psi.
08-24-2005 12:48 PM
Rick WI Holy crap, there is a ton of misinformation on here about pressure and tools. I do tons of work in the commercial and industrial market with compessor manufacturers analyzing compressed air SYSTEMS for more efficient operation. Never have I been in an installation that REQUIRED more than 100 to 110 setpoint at the compressor to operate any equipment you would normally see in an industrial application downstream of it. Never have I been in an installation where they would even consider operating the compressor at 175 to 200 PSI, that would be absurd, and extremely expensive.

I have worked and evaluated systems from 10 HP to 2500 HP, at companies like J Deere, Alcoa, Charter Steel, Briggs, GM and others. If you can build a car, tractor, forge wheels and make steel with 100 to 110 PSI air I suspect we should be able to tinker with our cars at home with the same, which you can.

What you need is volume to run tools. If you can run a DA for 25 minutes without a problem I'd say your in pretty good shape. After that period the line is probably spitting water and you'd want to stop anyway. The only thing a comressor does better than compress air is make water.

Air tools only need 90 PSI at the tailstock to operate properly and a peak efficiency. Therefore, if you have your compressor set 150 to 175 and it won't run the tools, it's not a compressor pressure problem. It's volume or a pressure drop in the line. I see this ALL THE time.

Unless you have some whoop de whoop super duper odd ball one of a kind tool 90 PSI tailstock pressure should be more than enough.
08-24-2005 12:21 PM
oldred Festive,
08-24-2005 11:45 AM
Festive57 Guy's, I thought I would pipe in for a moment... as I was reading this tread I was surprised at the large number of folks considering or suggesting upping the pressure on your stock air compressor. As others that have replied to this thread have pointed out, some compressor company's are not as "high grade" as others, so this means their tanks are not either. As oldRed stated about the tank bursting, this could happen very easily... I have a Sanborn 6HP, 80gal tank, single stage, my compressor kicks on at 90psi and shuts off a 120psi. I would like more cfm as well as pressure, but the tag on the side of the tank states very clearly max tank pressure is 150psi. so I really can not mess with it. Of course there is some safety factor built in but my point is, you should check to see what the rating of your tank is first before you up the pressure. Some tanks may not be able to handle it and you really do not want to be standing beside it when it does burst... Where I work, we pressure test housings that we build, these housing can be built from any number of thicknesses of materials, from #10ga. to 2" pl. our standard criteria is to pressure test up to 138in-H2O (which equates to approx. 5 psi... yes only 5psi.) anything over that pressure get Hydrostatic pressure tested. (they fill housing with water, water absorbs the energy, so the housing just splits at the weld seams or somewhere in the middle of a panel, usually where there was a flaw in the material) this is all for safety. All I'm saying is, be careful, if some young fella logs on and reads this thread and chooses to pump his pressure to 250!!! well it could be fatal...

Sorry, I was just concerned... thought I would throw my 2 cents in...
Bill
08-24-2005 11:12 AM
BondoKing Dang and here I thought it would lengthen the life since you are reomving the moisture and allowing air to flow both ways through the valve.... Red you are the man!!

BK
08-24-2005 10:56 AM
oldred JC, Actually I didn't think to mention it earlier but completely discharging a tank every day will theoretically shorten the life of it due to metal fatigue from excessive expansion/contraction. A tank will expand slightly each time it recharges and contract upon discharge but regular cycles are not as drastic as complete discharge.
08-24-2005 09:44 AM
oldred No it won't help it will just add unnecessary wear to the pump/motor. Might I suggest an automatic drain? I have one that came from Harbor Freight on my Ingersoll in my garage at home p/n 46960-7vga for about $17.00. They have one for around $10 dollars but it is rated at 100 PSI max but then we are only talking pennies anyway. I don't know what the max pressure is on the one I use but my compressor max is 150(6 HP two stage in case you may be interested) and it works just fine.
08-24-2005 08:22 AM
jcclark Another question for you compressor guru's.
Will a tank last longer if you drain out all the air
every day verses just draining out the water?
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