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  #1  
Old 10-31-2005, 10:11 AM
Coutel Coutel is offline
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air compressor advice needed

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I need an air compresor to run a pneumatic power hammer...

At peak, the hammer needs 30 cfm (cubic feet per minute) of air at around 90 psi.

To get a compressor to pump out that much cfm usualy requires 10 hp. But when you look at 10hp compressors, the prices jump big time..and I would also need 3 phase electrical supply (more money).

I can get two 5 hp compressors.....(a fraction of the cost of a 10hp)

Each compressor will throw out 18 cfm at 90 psi and each has its own 80 cu foot air tank.

I think I can join the two outlets with a T piece then run a single hose to the hammer.

Theory that the air between the two systems will always equalise to 90 psi, and I will have 160 gallons of air tank...combined should deliver in excess of 30 cfm (36cfm).....so think of it as a big air tank with two independant 5 hp electric compressors.


Can you see any problems?...will it work?


thanks in advance.


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  #2  
Old 10-31-2005, 05:35 PM
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Ray Rogers Ray Rogers is offline
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Hopefully, someone with a better background in fluid mechanics than I have will come along soon and nail this down for you. Until then, let me say that I think you are almost right.

I think the theory is that your method would result in a near doubling of the air flow but only if the two air sources could be brought together in an almost parallel manner. In other words, using a T connector might not get the desired results. "Theoretically", having a T would run the two streams together head on which would cause a large rise in pressure locally and a substantial decrease in cfm. Of course, the air will then move to the outlet but that stream will be some vector from the head on collision which I think will be at a higher pressure and lower cfm than what we really want. So, to get what you want you'll need to find a better way to connect the two sources than a T connector.

Again, this is just my admittedly weak understanding but I was just reading some papers on fluid mechanics and when I try to apply what i read to your situation that's how it comes out.....


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Old 10-31-2005, 06:49 PM
Coutel Coutel is offline
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Thanks Ray.
The air flow around the T had me thinking as well...idealy it needs to be a Y.


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  #4  
Old 10-31-2005, 06:56 PM
fitzo fitzo is offline
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Perhaps also a pair of check valves to prevent backflow?
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  #5  
Old 10-31-2005, 07:16 PM
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BigD BigD is offline
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I'm no expert either , but here is my 2 cents. I work in natural gas compression , if each compressor has a 1/4" outlet then you will probably need a 1/2" Y and 1/2" pipe from then on to the hammer , that way you won't gain pressure pumping 2 volumes of air into a single line.
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Old 10-31-2005, 07:37 PM
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Ray Rogers Ray Rogers is offline
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As I read it, backflow isn't so much the problem. The problem is more about the degree of interruption of the forward flow. That seems to create vectors of higher pressure with less flow - exactly what we don't want. The flow diagrams I saw seemed to indicate that the result would be more like what we want if the collisions of the moving streams were made as minimal as possible. Please remember once again, this is just my interpretation of some things I was reading on the internet....


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Old 11-01-2005, 07:15 AM
RJ Martin RJ Martin is offline
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I've never done this, but, I believe you want to connect the two tanks in series. This will double the volume of air available, but not affect the outlet pressure. The issue with smaller compressors is being able to supply a CONSTANT volume of air at the needed pressure. That is, not having to wait while the compressor runs frantically to try to get back up to pressure. With the two compressors in series, the downstream compressor can be replenished quickly by the upstream compressor. You might need a check valve between the two.

I'd call WW Grainger and ask. They could get you straight in about 2 seconds, and sell you whatever parts you need.


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  #8  
Old 11-01-2005, 08:28 AM
Matt Walker Matt Walker is offline
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Hey Coutel .. Glad to have met you at Bowies. Like the others I'm no expert either. But... What kind of hammer are we talking about? My hammer has a 2" x 12" cylinder. I don't think it needs anywhere near that volume of air. It does like a higher incoming pressure though. That enables a greater differential in the pressure settings and allows for great control. I like the high pressure side to be about 150 psi and the low setting to be about 80. Have you considered adding a reserve tank to store air pressure while reheating. Might be more economical than two compressors. My hammer will run over a minute, good on a 20 gallon storage tank with no additional air coming in. For my cylinder the 7.5 two stage seems to be was more than what is needed.
Good luck with it.....Matt....
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  #9  
Old 11-01-2005, 03:21 PM
Coutel Coutel is offline
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Thanks for replies...

I think I have solved the problem...and dont need to go the duplex route

My hammer is a Phoenix..150 (havent got it yet)...very powerful..and it likes to suck on air. ......It will run on a 7.5 hp, 23cfm..but if its going to be working hard like long draws on billets, then it can lose some power.....I think its peak performance is around 30cfm, and 175max psi...I just couldnt find a single phase compressor to match that performance...hence I was thinking of running two 5 hp compressors...or at the least a pony compressor to a 7.5hp 23 cfm one...

Did some research last night and found a new US compressor company...(Industrial Gold Inc.)....they make a 7.5 hp 1 phase that pumps out a whopping 32.7cfm @175psi..(34.1 @ 100 psi)..they even make a 10hp 1 phase which is unusual as most 10hp seem to be 3 phase.



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Old 11-01-2005, 03:36 PM
fitzo fitzo is offline
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Hi, Kevin,

I have zero knowledge about the company you mention. However, compressor companies are notorious for over-rating their equipment.

You might find this informative reading. It came from a Google on "air compressor ratings". There were a lot more hits.

http://truetex.com/aircompressors.htm

Good luck with your selection process.
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  #11  
Old 11-01-2005, 06:44 PM
Coutel Coutel is offline
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Quote:
Originally Posted by fitzo
Hi, Kevin,

I have zero knowledge about the company you mention. However, compressor companies are notorious for over-rating their equipment.

You might find this informative reading. It came from a Google on "air compressor ratings". There were a lot more hits.

http://truetex.com/aircompressors.htm

Good luck with your selection process.

I am far too trusting .....hope I am not being mislead cos I have ordered one!....


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Old 11-01-2005, 07:22 PM
fitzo fitzo is offline
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What kind of amperage do they claim that draws, Kevin, if you don't mind my asking?

I just ran 7.5HP @ 230V through this calulator and it said max draw would be a whopping 40A! Gonna warm up those old power lines. Mind you, that's a "generic" number, and they make that caveat.

http://www.shipcopumps.com/mathwizar...oramperage.asp

Hope you really enjoy your hammer. Though I have a press, I love hammers. There's a certain panache that a press just can't duplicate!
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  #13  
Old 11-02-2005, 07:30 AM
Coutel Coutel is offline
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Hi Mike.

The compressor manufacturer said it would draw 31 amps and would need a 60 amp breaker. ..


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  #14  
Old 11-02-2005, 11:07 AM
fitzo fitzo is offline
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Cool! What a beast of a machine! I hope you'll share a foto of the whole setup once you get hammer and compressor all up and running.

Have fun, Kevin!


Congrats, too, on recent accomplishments!
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  #15  
Old 11-02-2005, 06:09 PM
Wiggins Wiggins is offline
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Kevin,
I am running a 75 bullhammer, and I bought the compressor Tom recommended. I have to be working a really large billet for it to kick on and run for any period of time before I am out of heat. Your hammer will probably need more air than mine, but I have no idea how much more. I do know that having no restrictions between the compressor and hammer is a good idea. Keep an eye on inside dimensions of all your plumbing. And let me know when you pick up the hammer. You will only be about 30 mins. from the house.
Bill
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