Please explain me air compressors

Please explain me air compressors
Air compressor specs seem to be all over the map. For example, the latest Harbor Freight flyer
features two. 1) 2HP 3.8CFM at 90PSI 2) 4.5HP 4.4CFM at 90PSI
Why can't 4.5HP give me 8.55CFM??
They're also advertising a 500,000 WATT rechargeable spotlight. Yes, watt!! That's gotta be some BRIGHT light. I'll bet they have a problem with battery life tho...
mike
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forth from the murky depths:

All on 120v and under 7amps, right?

I'm sure they meant 500k oil-burning-lamp-power or candlepower there but some Japanese translator of the Thai documentation of the Indian product made a wee mistake with the 4th translation into Chinglish.
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On Sat, 29 Nov 2003 18:21:28 +0000, Larry Jaques wrote:

From the owner's manual (presumably),
"Thank you to owner proud happy watt light! Happy watt light make dark bright long time! Happy watt light are have many long time setting. Low setting are many 100 watt. Long time are 2 hour. Medium setting are many 500 watt. Long time are 30 minute. High setting are many 500,000 watt. Long time are 5 millisecond."
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On Sat, 29 Nov 2003 15:42:11 -0500, Artemia Salina

Right. That reminds me of the cute little Vietnamese girl I used to work with who once said--very enthusiastically I might add--"I speak very English!"
BTW, I have one of the 500kCP cordless spots and they're VERY nice to have. Mine is a Vector and has an internal gel cell which lasts quite a while on a charge. It was definitely worth $9.95 at Target a couple years ago.
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    That is because they don't all lie the same way. :-)

    The meaning of this comment is that you *can't* get the claimed specs form a standard 120V wall outlet. The 4.5HP converts to 3330 Watts (assuming an approximation of 740 Watts per horsepower), which from a 120V outlet would draw 27.75A (neglecting efficiency corrections).
    Most residential outlets are 15A maximum, and some are 20A, which is still well below what you need to get 4.5HP at 120V. (You *could* do it from a 220V outlet, however.)
    Some of the makers and/or vendors take the current drawn for a few milliseconds from a locked rotor just before the winding wires go up in smoke.
    You're better off working from the CFM at PSI ratings. I don't think that they have done as much to them -- yet. :-)
    Enjoy,         DoN.
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something ......and in reply I say!:

Ignoir the other crap. The CFM @ PSI is all you should worry about. "HP" is BS.
To illustrate, the CFM/HP on those, as claimed, is very poor. You should be able to get at least 5 CFM from a jenwine 2HP machine, and probably more on a decent belt-drive machine.

It's OK. As long as you only want to look at the same spot, the whole scene will be burned permanantly into your retina anyway.

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brought forth from the murky depths:

Does anyone have any experience with HF's new line of oil-bath compressors? The 2hp (4.5hp w/ 4.4cfm@90psi) vertical tanker is only $169 on sale. I'm wondering if I should even try to rebuild my 1hp compressor if new pumps go for that low price. A $35 garage sale item, she starts knocking a bit at pressures over 20psi. I haven't torn her down yet so I don't know if the problem is piston slap or bearings.
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wrote something ......and in reply I say!:
sorry. That was meant to be permenantly....

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Old Nick wrote:

It should be permanently.
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wrote something ......and in reply I say!:
sorry. I will put a smiely next time <G>

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mike writes:

http://www.truetex.com/aircompressors.htm
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Richard J Kinch wrote:

Excellent. Even I could understand that. Thanks, mike
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Why is it that I don't see the term 'Free Air Delivery" in this thread? After all, FAD @ (some) rated pressure is the opeative specification of a compressor. Here in Oz there is an organization (ACMGA, Air compressor Manufacturers something of Aust), and retailers who are members always quote the FAD for any compressor they sell. You don't generally see them selling the $99 oil-less units etc, but there are still plenty of reasonably priced machines that _do_ have a FAD spec'd.
My observation is that if you insist on buying a cheapy without any FAD spec, it will probably deliver around 0.5 - 0.7 times the swept volume (i.e. 0.5 - 0.7 times what is generally the advertised CFM). Exactly what the rated HP is doesn't matter a toss, within reason.
Comments?
Roger
mike wrote:

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wrote something ......and in reply I say!:

Part of the problem is that FAD has been argued about. Some think it's @ a pressure. Others believe it's at _any_ pressure, as long as the air flows that fast.
I sit with the first.
But since XCFM @ Y PSI can ony be worse than FAD if there is any restriction, it's assumed that FAD is implied. The irony is that you have to restrict the flow in order to measure the "Free" Air delivery and maintain a pressure for any unit. <G>

Yep. Fair enough. I have a "12CFm" cheap(er, not cheapest) that will do 7-8CFM @ 90 PSI **************************************************** sorry remove ns from my header address to reply via email
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