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Old 02-27-2008, 08:45 PM
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What is RUNNING HP

I'm looking for a air compressor, I see this 5.5 RUNNING HP or 5.5 peak HP . I don't care if it's running or peaking, I do care about REAL HP.... should i look at the amps of the motor? what gives.??????????

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Old 02-27-2008, 09:50 PM
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30 years ago they were rated at running horsepower. Peak is just how much it draws when it starts, but lately some low-life companies started using peak HP in their ads because it sounds so much more powerful to the unenlightened, who will then drop more money than it's worth on their cheapo toy compressor.

If you can find out how many amps one draws under normal running conditions, you can use that and the voltage to find the HP rating. Multiply voltage times amperage, and divide by 746. Volts x amperes = watts, and 1HP = 746 watts.

There's usually a plate riveted to the motor that tells you how many amperes it draws.
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Old 02-27-2008, 10:49 PM
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Quote:
Originally Posted by jimfulco
30 years ago they were rated at running horsepower. Peak is just how much it draws when it starts, but lately some low-life companies started using peak HP in their ads because it sounds so much more powerful to the unenlightened, who will then drop more money than it's worth on their cheapo toy compressor.

Exactly! but actually calling them just low-lifes is being too polite to the [email protected]##%@*^s


Awart, You are finding out just how confusing it can be trying to figure out how a compressor will perform by looking at the (mostly) ridiculous claims made by the manufacturers. As a general rule you can figure a true 5 HP motor (rating) will be rated at least 23 amps and probably higher and the very common 15 AMP motors will be about 3 1/2 HP no matter how much HP is claimed, usually about 6 to 6 1/2 or even 7. About the best way to determine how a compressor will perform is to just ignore the power numbers and look for the CFM rating but unfortunately even this can often be misleading as the b%#&^$s tend to exaggerate these numbers too, just not as bad as the power numbers. CFM can be rated several different ways but the two most reliable methods are SCFM (standard cubic feet per minute) and ACFM (actual cubic feet per minute) but sometimes ACFM is used to mean ASSISTED CFM which is pure nonsense so when looking at ACFM ratings make sure which it is. Fortunately this "tank assisted" nonsense did not seem to catch on and is not very common anymore but you could still run into it. Either SCFM or ACFM ratings, while somewhat different, can be used to determine what a compressor is capable of because they will both be fairly close. Personally I think SCFM is the better way to rate a compressor but this is a subject that even the engineers will disagree on so go by either rating and you will be fine. The inflated CFM claims are usually made by the "cheapie" outfits and most of the big name companies are usually fairly honest about CFM numbers but one exception to this is Ingersoll Rand who has some ridiculously inflated claims on some of the units aimed at the small shop.
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Old 02-28-2008, 04:01 AM
 
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What is "running HP"?

It's the New! Improved! ZXR99-Q(r, tm, pat.pend.) miracle running HP*!

It hisses! It spews! It makes your air tools last 3 times longer**!

Wait, there's more(sm, c)! Our new miracle running HP* quadruples your free time***! Take a vacation and get reacquainted with friends and family****!

Hurry! Supplies are limited*****!



*HP not to be confused with horsepower or Hewlett-Packard. Any resemblence to horse puckey is purely coincidental. No, seriously. It won't grow tomatoes, no matter how it smells.

**Air tools cannot wear out if they cannot be used due to insufficient air volume.

***It takes 4 times as long to get enough air to do useful work if you have 1/4 the compressor power you need.

****Friends, family and neighbors will shun your garage if you buy into "running HP" because the compressor runs constantly, and nobody wants permanent hearing damage. On the plus side, you get fewer interruptions from people while waiting and waiting for the air pressure to build up. On the minus side, if you do hang around waiting for that elusive air pressure, your children will be in expensive therapy for years trying to find out why you were always yelling at everyone.

*****Supplies of runney horse puckey, er, I mean, running HP are limited because those folks who haven't completely wrecked their hearing or lost all their friends, got tired of waiting for air pressure, put down their air-starved tools, wiped their feet and are warning others to stay away from tricky number games on labels.

Last edited by grouch; 02-28-2008 at 04:03 AM. Reason: spellung
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Old 02-28-2008, 08:36 AM
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Quote:
Originally Posted by grouch
What is "running HP"?

Wait, there's more(sm, c)****! Take a vacation and get reacquainted with friends and family****!
While you wait for the pressure to build up on some of those things!






Best explanation I have heard yet and makes MORE sense than a lot of those labels stuck to the tank!
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Old 02-28-2008, 08:50 AM
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Awert, Seriously that is a good question but the point is that most of the "econo" compressor labels are so ridiculous they are simply a bad joke and it it is nothing more than a guessing game as to how well the outfit will work. As for how much power the motor has just ignore the HP rating and look at the data plate on the motor, it is the AMPs that tell the real story, that thing is mandated by law and they won't mess with those numbers! Look to some of the more honest outfits, like Eaton, and compare their performance numbers to similar size econo compressors if that is what you are looking at, or better yet shop for the Eaton or maybe a Quincy if want the best and don't care to spend the extra money.
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Old 02-28-2008, 04:49 PM
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I'm running

I'm not pro but i'm not a moron either, I can see what looks like over rated "facts"... What is the difference between single and 2 stage??
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Old 02-28-2008, 08:21 PM
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A single stage simply forces air directly from independent equal size cylinders directly into the tank while a two stage uses a large cylinder to force air into a smaller one before sending it into the tank. The purpose of the two stages of compression is to obtain both higher volume and higher pressure for a given amount of horsepower, it simply is more efficient this way. With a given HP rating a compressor can deliver a high volume at low pressure or a low volume at high pressure but not high volume and pressure at the same time, using one large piston for the first stage and then a smaller one for the second stage helps get around this problem. It also uses a cooler during the transfer which allows for cooler air in the tank but it's main purpose for the cooler is to dissipate some of the heat prior to the second stage of compression which will allow the compressor to be designed to be able to deliver a higher pressure. Think of a single stage as a car with only one gear- you could go fast with little torque or you could have lots of torque but little speed so you would have to compromise. The two stage could be thought of as a car with a two speed transmission allowing both a higher top speed but also more torque at low speed. Hope that was not confusing.
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Old 02-29-2008, 10:50 AM
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what is:

Great answer, I can even understand that...I never knew that though...
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