Air compressors.

[Anonymous-0]

I want to do some serious sand blasting ie large tractor parts, My 5hp 60 gal 135 psi max air compressor cant handle it. The cheapest way seems to be buy another compressor of similar rating and let them both feed the pressure sand blaster. Any drawbacks.?

 

[Anonymous-0]

When I selected a large compressor for my former company I remember that if you had 2 compressors feeding a large mfg. plant you had to have a sequencer to adjust both compressors to turn on and feed a receiver tank. I would do a search on the net to see if a pressure switch located in the receiver tank is needed to turn on both compressor motors. I am not an expert in air compressors and hopefully somebody else here will chime in and correct me if I am wrong.

 

[Anonymous-0]

What is important is the (CFM)Cubic Feet per Minute produced at 90 PSI.which is the required pressure for most air tools for their rated work output.Volume is your problem.The compressor you got would be fine for painting or tools that need less than the output volume stated on the compressor.You need more volume not pressure. CENTAUR

 

[Anonymous-0]

If you want to do honest to goodness sand blasting with a pressure pot, you need an honest to goodness compressor capable of moving enough air to do the job. Electric compressors just don't cut the mustard.

Here's mine

<a href="http://pg.photos.yahoo.com/ph/chuckhanna/detail?.dir=5ca9re2&.dnm=5d9fre2.jpg">Atlas-Copco Compressor</a>

Charles

 

[Anonymous-0]

You can do that -- be sure the pressure switches are set the same. Don't buy a two stage if you intend to continue using your single stage. You can't get the off pressure of the 2 stage low enough to allow the single stage to come on, at least mine doesn't, there may be a way to make it work, though. My 24 cfm 2 stage works fairly well, just slow.

 

[Anonymous-0]

20 to 50HP of compressor is minimum if you are serious.

 

[Anonymous-0]

If you must gang two compressors together, install check valves on the outlet of each tank and this way the higher pressure from one tank won't back up into the other and keep its pump from coming on. Each compressor will operate independently of the other depending on how much air you are drawing.

Charles

 

[Anonymous-0]

If the compressors are the same, 2, two stage or 2, single stage use one pressure switch to operate the maginetic starters for each. It does not matter that way about horse of either unit. Doing it this way you can tie several compressors together. One could be a 2hp the other a 20hp as long as the stage is the same.

 

[Anonymous-0]

Just tie both machines into the same line. Set the pressure range on one to be lower than the other so it cuts in once demand is high. The higher set compressor will carry the bulk of the load for light to medium use, the secondary machine will cut in and help maintain pressure under heavy load. Cut in and cut out of the secondary compressor should be lower than the cut in of the primary compressor. It is a good idea to set the secondary machine low enough so that there is not a risk of both machines starting at once, since that will likely be too heavy a current draw for your service. Having said that, I agree with other posters that any serious sandblasting requires a beefy setup, not a bunch of small compressors running 110% that will still likely not keep up. I used to sandblast with a 10hp IR two stage compressor at work and it was all it could do to maintain 80psi with even a small nozzle.

 

[Anonymous-0]

I don't agree with the simultaneous starts advocated below. The current draw is highest when a compressor is started from rest. Why would you want to rob volts (electrical pressure) from both machines at that moment? That condition causes amps to rise and tripped breakers.

The standby compressor, that is reserved to augment CFMs, should have its cut-in and cut-out set below the everyday shop compressor. When the auxillary compressor is not needed, it is not permitted to run by putting its breaker on off. When starting a sandblasting job, the breaker is activated. The compressor pressure switch will keep the auxillary compressor shut down until the main compressor air receiver loses pressure due to consumption. At that point both compressors will be running as the second one is started.

The sandblast nozzle should be sized so that both compressors run continuously. When stopping to refill the pot, the auxillary compressor will shut down first.

This is called "lead/lag". It is used in industrial situations, such as sewage pumping, air compressing, HVAC, and , for all I know, electrical generating. The lead/lag units are often pregramed so that the machines take turns running the base load.

I was recently in a hospital where four 103 CFM reciprocating compressors were pumping into one air receiver. They were tied into a panel that automatically started, stopped, and scrambled the hierarchy of each unit. The controller could sense the draw and fire up as many compressors, in turn. as needed to meet the load. The off/on signals were progressive.

I believe this compressor management feature is more energy efficient than running one large continuous run compressor fitted with unloader valves. It may also be more efficient than running a screw type compressor with a throttle.

 

[Anonymous-0]

Roger, I kinda stepped on your toes. It took me more than an hour to write my post as I was multi-tasking. At any rate, we are in agreement.

In a few days, I'll have a question regarding a 20hp Kellogg fitted with unloaders. Somebody ripped it out of a building and I am not sure how to wire it.

 

[Anonymous-0]

You may want to check your nozzle size , some wear very quickly and demand more air when worn. I use a 7.5 hp IR ,with a3/32 nozzle and run until a 5/32 drill bit will slide in, usually about 7 or 8 80# bags before replacement at around100 psi on sheetmetal, 150 psi on heavy stuff . hope this helps gh

 

[Anonymous-0]

Thanks for the help. Answered my questions.

 

[Anonymous-0]

Get a tungston carbide nozzel. As a hobbyist, you will never wear it out. Use several ceramic nozzels to figure out what size you should buy.

BTW, it is cheaper to buy a good nozzel than countless throw-away equivalents.