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Air compressor

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fullmer
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PostPosted: Tue Oct 23, 2012 1:44 pm    Post subject: Air compressor Reply to specific post Reply with quote

Have a 60 gallon upright Coleman air comp. 6.5 rated hp it
has a 3/8 discharge line to tank would it help to increase it to
1/2 , it can't. Keep up with my grinder.
 
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hoof print
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PostPosted: Tue Oct 23, 2012 2:14 pm    Post subject: Re: Air compressor Reply to specific post Reply with quote

probably does not have anything to do with the outlet size. What is the rated output of the compressor (cfm) at the psi that the grinder requires? Grinders are air hogs, the compressor may not be enough to run it.
 
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rodm1
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PostPosted: Tue Oct 23, 2012 2:47 pm    Post subject: Re: Air compressor Reply to specific post Reply with quote

I bet yours is oil less how many amps is the motor? Get a oil lubed 5HP compressor.
 


Last edited by rodm1 on Tue Oct 23, 2012 2:48 pm; edited 1 time in total
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old
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PostPosted: Tue Oct 23, 2012 3:04 pm    Post subject: Re: Air compressor Reply to specific post Reply with quote

Increasing the line size from the compressor to the tank may help some but again it all depends on how much CFM the compressor is rated for and how much CFM it takes to run that grinder. Many tools take a lot of CFM and if say the grind needs 15CFM at 90psi and the compressor if only rated at 12CFM at 90 psi it will not help any
 
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RGMartin
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PostPosted: Tue Oct 23, 2012 3:25 pm    Post subject: Re: Air compressor Reply to specific post Reply with quote

rodm1 wrote:
(quoted from post at 18:47:43 10/23/12) I bet yours is oil less how many amps is the motor? Get a oil lubed 5HP compressor.



If it is the unit I am thinking of, they were a "real" 3hp. 15A 220v.
 
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markiz41
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PostPosted: Tue Oct 23, 2012 5:01 pm    Post subject: Re: Air compressor Reply to specific post Reply with quote

This is interesting, anybody know how many cfm you can push through a 3/8 cross section? I know it's pressure related, so let's say 90 psi..
 
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hoof print
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PostPosted: Tue Oct 23, 2012 7:02 pm    Post subject: Re: Air compressor Reply to specific post Reply with quote

markiz41 wrote:
(quoted from post at 02:01:57 10/24/12) This is interesting, anybody know how many cfm you can push through a 3/8 cross section? I know it's pressure related, so let's say 90 psi..


I'm tell ya mark, CFM at rated psi is what you should be investigating
 
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Stick welding
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PostPosted: Tue Oct 23, 2012 8:25 pm    Post subject: Re: Air compressor Reply to specific post Reply with quote

Air hose size has a lot to do with CFM! If it's an
air powered angle grinder, they take a lot of CFM.
A 7" air grinder will need a 1/2" or larger air
line to get enough CFM. It's no different than a
water hose. Say you have a 4" pump that puts out
750 GPM but you only have a 2" hose. There's no
way a 2" hose will flow 750 GPM. A 3/8" hose may
flow enough CFM but it depends on how much the
grinder needs and the output of the compressor.

As to the original question, the compressor in
question falls into a grey area as it is not a
true 6 1/2 HP motor. It's probably closer to a 1
HP especially if it runs on 115 volts or maybe 2
HP on 230 volts. It it was a 7 1/2 HP would make
more sense because they actually make a true 7 1/2
HP motor but it is about 3 times bigger than the
fake 6 1/2 HP and would cost about 3 times as much
as the whole compressor just for motor alone. I
suspect the compressor may be too small to run the
grinder once the reserve capacity in the tank is
used up. Just like using a big impact wrench, it's
good for a few minutes but then the compressor
alone won't keep up.
 
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MarkB_MI
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PostPosted: Wed Oct 24, 2012 1:28 am    Post subject: Re: Air compressor Reply to specific post Reply with quote

By "can't keep up", I assume you mean the pressure drops below the 90 psi regulated pressure normally used for air tools. If that's the case, then the diameter of that air line is unlikely to be the issue. If you're using a 3/8" air hose from your tank to your tool, there's much more pressure drop in the hose than in the short compressor-tank connection.

Consumer-grade compressors are notoriously overrated. A true 6.5 hp air compressor will draw close to 30 amps at rated pressure and CFM. There is a reason Coleman only used a 3/8" line: that's all it needed.
 
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George Marsh
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PostPosted: Wed Oct 24, 2012 4:12 am    Post subject: Re: Air compressor Reply to specific post Reply with quote

Agree, grinders are air hogs. Ever think of usings electric grinder? I got rid of all my pneumatic sanders and grinders. Use electric instead. Use a dimmer switch and a receptical to make grinders variable speed. Electric grinders and sanders us way less electricity.
George
 
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Ken Macfarlane
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PostPosted: Wed Oct 24, 2012 4:49 am    Post subject: Re: Air compressor Reply to specific post Reply with quote

Thats a good point, a 600 watt grinder is about equal to an air grinder that needs a 3500 watt compressor running non stop
 
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markiz41
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PostPosted: Wed Oct 24, 2012 5:05 am    Post subject: Re: Air compressor Reply to specific post Reply with quote

Sure electric ones are great. But try scrubbing a gasket off a differential housing with one - it won't even make past the sway bar!
 
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fixerupper
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PostPosted: Wed Oct 24, 2012 9:12 am    Post subject: Re: Air compressor Reply to specific post Reply with quote

It stirs me up a bit when I see the compressor sales companies using deceptive advertising, calling a 3 HP motor a 6.5. The CFM's is listed on some small barely visible tag. They probably get by with it because it's a CALCULATED 6.5.

I got burned by Craftsman years ago, buying a new table saw that was advertised as 3HP but was really a 1.5 HP. Craftsman lost my business for power tools after that. Jim
 
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George Marsh
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PostPosted: Wed Oct 24, 2012 9:24 am    Post subject: Re: Air compressor Reply to specific post Reply with quote

Ken,
I'm a fan of dewalt tools. Close enough to John Deere yellow. I have three 4.5in dewalt right angle grinders. The biggest ones use 10 amps, 120v, 1200 watts. A 6.5 hp air compressor is going to use way more than 1200 watts. I can't stop my grinders. I have a wire brush on one, a metal cutting disk on another and a grinding disk on the other. I use the dimmer switch on the wire brush. The grinder can do serious damage if it gets away from you. Will never go back to pneumatic tools. Don't leave home without my grinders.
George
 
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J-TEX
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PostPosted: Wed Oct 24, 2012 9:36 am    Post subject: Re: Air compressor Reply to specific post Reply with quote

213 CFM @90 psi through 3/8 hose
 
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