compressors -- comparing apples to apples

[cglasgow]

Hello! This is my first post here! I've been browsing the archives but although there's lots of compressor info, I couldn't find quite the answer I'm looking for.

I'm considering one of two compressors. Same seller, +/- same price. Both have 60 gal vertical tanks. The first is a Campbell Hausfeld VT627504AJ. 4 hp 240V motor, twin cyl cast iron (made in USA!) single-stage compressor. Splash lube. 10.2 cfm @ 90 psi, 11.5 cfm @ 40 psi. Looks like a reasonably well-built consumer-grade unit. About 4 years old.

The second is about 50 years old, Gilbarco with Quincy 310 compressor. Two stage, pressure lube, with 1.5 hp, 240V motor (newer than the rest of the unit, but still old). This thing looks very industrial and I'm sure will easily outlast me. Obviously very well built, and looks like reasonably well maintained (or at least not beaten to death).

What I have been unable to find, though, is apples-to-apples CFM numbers. The only thing I can seem to find about a Quincy 310 is that it's 4.06 CFM @ 400 RPM & 175 psi, and 9.35 CFM @ 920 RPM & 175 psi. 9.35 CFM is not that much less than 10.2 I suppose, but 90 psi is quite different than 175 psi so I've no idea what the Quincy would make at 90 psi (the CH wouldn't even be capable of 175 psi I suspect). I'm assuming the Quincy will produce more air, but how much? Any thoughts?

Thanks!!!
-c

 

[larry_g]

I was wandering around the internet looking at Quincy numbers and the out put depends on the HP of the motor driving the pump. It takes specific HP to drive the pump at a given RPM. So quincy rates their CFM at speeds and then has a recommended HP to run that speed. Me I would go with the Quincy just because of there parts and support. You don't say what your intended use is so it's hard to guess what you may need for CFM.

On edit
I went looking for the chart I found but did not find it. I did find that the 310 is rated for 1.5 to 3hp so I would assume that you would get on the lower end of the CFM spec with a 1.5 motor. If you can do an amp draw on the motor you can see if the pulley ratio is correct. The motor should be approching FLA when the pump kicks off. If it is drawing overcurrent then your pulley ratio is to low and visa/versa.

lg
no neat sig line

 

[930dreamer]

What will the compressor be used for, a 1.5 hp compressor will air up tires etc, but not much more.

 

[cglasgow]

Thanks for the input. I'd like to be able to to everything from airing up tires to sandblasting. At the price I can get one of these, there's a little left in the budget to upgrade the motor on the Quincy if necessary (assuming I can find a used one at a reasonable price, and it doesn't have to happen immediately). I'd just like to know what I can expect out of it....

Thanks!
-c

 

[930dreamer]

With either compressor, you'll be hard pressed to sand blast, the CFM is too low.

 

[cglasgow]

Again, thanks everyone for the input. What I'd really like to find out, though, is what sort of cfm (given sufficient hp) that a Quincy 310 would output at 90 psi, so that I can compare the two compressors on equal terms (at least in terms of output -- the Quincy unit is obviously higher quality).

Sorry to seem insistent, but I'm sure one of the other (or both) of these will sell quickly....

Thanks!!!
-c

 

[930dreamer]

http://www.mesaequipment.com/Html/Products/Quincy/qr25_basic.html

Try this

 

[cglasgow]

http://www.mesaequipment.com/Html/Products/Quincy/qr25_basic.html

Try this

Thanks 930dreamer! That's where I got the 175psi figure I referenced in my original post.

Cheers!
-c

 

[rodm1]

What is he asking for them? If under $200 I think I would take a chance on the "Gilbarco with Quincy 310 compressor" you could replace the motor if you needed more CFM. Its industrial 175psi way more air with pressure lube and if you looked around you should be able to find a 5hp motor cheep.

Plan on adding a 3-5hp motor if you get the Quincy. You mite be able to add a unloader to it not shire on that.

I think at 400rpm the Quincy will give you 7cfm @ 90psi and at 920rpm the Quincy will give you 17cfm @ 90psi.


I think this post is what you are looking for in order to convert you CFM's.
http://www.physicsforums.com/showthread.php?t=155966

 

[cglasgow]

Well, I own them both (for now). A buddy is buying whichever one I don't keep.

I ran a test -- pressurising them from 0 to 120 psi. The CH took 5 min 17 seconds. The Quincy took 9:15. I was a little disappointed -- I expected the Quincy to do better than that. The CH shut off at 130 psi. I don't know what the cut-in pressure is. The Quincy shut of at 180 psi. Again, don't know what the cut-in pressure is (haven't tested it yet).

The Quincy has a 1725 rpm motor on it and based on the pulley size I calculated that the compressor is spinning at 522 rpm. So there's so potential to up the output from the Quincy. And the Quincy is much nicer to be around when it's running.....

Decisions, decisions.....

 

[cglasgow]

I think this post is what you are looking for in order to convert you CFM's.
http://www.physicsforums.com/showthread.php?t=155966

Just saw your edit -- that's exactly the kind of thing I was looking for! Thanks!!!

-c

 

[hofferwood]

Hello,
Now that you have 'em try this http://www.ehow.com/how_5001852_calculate-cfm-air-compressor.html

Uncomplicated

Chuck

 

[cglasgow]

Hello,
Now that you have 'em try this http://www.ehow.com/how_5001852_calculate-cfm-air-compressor.html

Uncomplicated

Chuck

Perfect! I'll report my findings....

Thanks!
-c

 

[larry_g]

Well, I own them both (for now).
I ran a test -- pressurising them from 0 to 120 psi. The CH took 5 min 17 seconds. The Quincy took 9:15. I was a little disappointed -- I expected the Quincy to do better than that.

And the Quincy is much nicer to be around when it's running.....

Decisions, decisions.....

Two things

1. Are the tanks equal in size for your timed test?

2. The second statement is the sound of quality, and sound is a large factor with living with a compressor.

lg
no neat sig line

 

[cglasgow]

Two things

1. Are the tanks equal in size for your timed test?

Yes -- the test would be meaningless otherwise. ;-)

2. The second statement is the sound of quality, and sound is a large factor with living with a compressor.

Indeed! With the CH, I'll want to either wear hearing protection or leave the room when it's running -- it's that loud. The Quincy whispers in comparison.

I ran some numbers. Averaged over several tests, the Quincy is making about 5.7 CFM. If we assume that the output curve is linear between 4.06 CFM @ 400 RPM and 9.35 CFM @ 920 RPM, then we'd expect about 5.3 at the 522 RPM it's running. But the endpoints were specified at 175psi, and I tested between about 100 and 140 so it being a little higher doesn't surprise me that much.

The CH, on the other hand, is making about 11 CFM over the same range. These numbers may not be correct in an absolute sense, but I think they're accurate enough for comparison. (I'm making the big assumption here that the gauges on both machines are accurate, but both seem to cut out right at about an indicated 40 psi after they cut in, so they're probably not too far off). Even if I spin up the Quincy to its max rated RPM, I'll still not see quite the numbers of the CH (probably).

I can't find my clamp-on ammeter right now so I don't know how hard the motor is working. A simply pulley change might be all that's needed to boost the output. I know I won't be able to spin it at 920, but I might eek out a few more RPM....

On the other, other hand (we're up to three hands now ;-), the CH, in addition to being NOISY, runs much hotter than the Quincy (as you'd expect). So I'm sure that it won't be around in 2054, 50 years after it was made. The Quincy survived. But then I don't expect to be around in 2054 either at the rate I'm going!

On the fourth hand, I'm a little concerned as well about the tank on the Quincy. I can't see inside it (obviously) but it's got a weird drain arrangement I've never seen. The drain connection is about a foot above the bottom of the tank and screws into a 3/8"(?) bung. Inside the tank, it has a flexible dip tube that goes down to the bottom. Even if this could completely drain the water (which I doubt), it would appear to be prone to clogging, and indeed seems to be partially blocked. I'm wondering if it was installed because the the bottom drain stopped up with rust? There's only a pipe plug there now. I haven't tried removing it. I think that's going to mean laying the compressor on its side, and it's a heavy sucker.

So far neither one is screaming "Keep me!" louder than the other.... :-(

EDIT: found an error in my math (turns out there are actually 60 seconds in a minute -- who knew? ;-) The Quincy is more on the order of 7.8 CFM rather than 5.7. That puts it farther off the line based on the published figures, but again this is at a lower pressure than published, plus I don't know if the relationship of flow to RPM is linear. Puts it at less of a disadvantage relative to the CH, though!