Welcome! Please use the navigational links to explore our website.
PartsASAP LogoCompany Logo Auction Link (800) 853-2651

Shop Now

   Allis Chalmers Case Farmall IH Ford 8N,9N,2N Ford
   Ferguson John Deere Massey Ferguson Minn. Moline Oliver

Discussion Forum

Air Compressor HP Ratings

Welcome Guest, Log in or Register
Author 
TWJanak

01-15-2008 16:28:19




Report to Moderator

Why can I buy a 15 CFM @ 175 psi compressor with a 5 HP electric motor, but with a gas engine the engine HP is 10-12?

I have a 5 HP compressor (just the pump) that is rated around 17 CFM at 175 psi. The literature says its a 5 HP pump. I assume a 5 HP electric motor would run it, but I doubt a 5 HP gas engine would do as good.

That said, I'm going to try the 5 HP gas engine anyways on my pump, it's all I have. I'll just regulate down to 110 psi or so.

[Log in to Reply]   [No Email]
TWJanak

01-16-2008 07:07:32




Report to Moderator
 Re: Air Compressor HP Ratings in reply to TWJanak, 01-15-2008 16:28:19  
It will have an unloader when it hits the cutout pressure (110 psi). During pumping, the engine will run at max HP (3600 rpm) and after cutout, idle down because the pump is unloaded.

That being said, I don't see why 5 HP gas engine at max HP (3600 rpm) is any different than than the electric motor. They should both be putting out rated HP. Obviously it is though, all the ones I see for sale have twice the HP if gas powered.

[Log in to Reply]  [No Email]
Bus Driver

01-16-2008 04:45:07




Report to Moderator
 Re: Air Compressor HP Ratings in reply to TWJanak, 01-15-2008 16:28:19  
For gasoline engines, the HP rating is the maximum that the engine will develop. With electric motors, the HP rating is the continuous output, for the time rating of that motor. For short periods of time, electric motors can deliver at least twice their rated horsepower. Amperage draw increases sharply and the motor gets hot in such situations. But a compressor has a heavy load for part of a rotation/revolution and a light load for part of a rotation. Electric motors respond better and faster to varying loads. The short duration loading during a rotation/revolution of a compressor works well for electric motors.

[Log in to Reply]  [No Email]
IH2444

01-15-2008 23:12:52




Report to Moderator
 Re: Air Compressor HP Ratings in reply to TWJanak, 01-15-2008 16:28:19  
Umm doesn't gas powered compressors need an unloader valve that is not required on electric compressor pumps ? something is needed to stop the pump from pumping once pressure is reached.
an electric motor one starts and stops, but the gas engine keeps on running.



[Log in to Reply]  [No Email]
KEB1

01-15-2008 19:21:22




Report to Moderator
 Re: Air Compressor HP Ratings in reply to TWJanak, 01-15-2008 16:28:19  
The difference has very little to do with running horsepower (horsepower is horsepower) and everything to do with starting torque. A capacitor start electric motor generates maximum torque at or near stall, a gas engine generates no torque at stall and not much at low speeds. A larger gas engine is required to provide sufficient torque to start the compressor without stalling, not to keep it running once it has started.

I'll bet the gas engine is running on part throttle (and therefore not putting out its full rating) except when it has to start the compressor. Its probably also running a lot slower than the speed at which it produces the rated horsepower. Contrast this to an electric motor which runs at a (more or less, anyway) constant speed regardless of load.

Keith

[Log in to Reply]  [No Email]
markiz41

01-15-2008 18:20:08




Report to Moderator
 Re: Air Compressor HP Ratings in reply to TWJanak, 01-15-2008 16:28:19  
5hp gas is about 2.5hp electric. It will run your pump, you'll just have to slow it down some by putting a smaller pulley on the engine. Regulating the cutoff pressure down like you said is also a good idea. You won't get 15 cf, though, maybe 10 or 11 at 110 psi.



[Log in to Reply]  [No Email]
JMS/MN

01-15-2008 18:12:14




Report to Moderator
 Re: Air Compressor HP Ratings in reply to TWJanak, 01-15-2008 16:28:19  
Normally a 1 to 3 ratio comparing electric motor to gas engine. And that motor labeled 5 HP in the advertising is probably about 4hp. Check the motor nameplate for amperage draw. Watts equals Amps times Voltage. 745 watts equals 1 hp.



[Log in to Reply]  [No Email]
[Options]  [Printer Friendly]  [Posting Help]  [Return to Forum]   [Log in to Reply]

Hop to:


TRACTOR PARTS TRACTOR MANUALS
We sell tractor parts!  We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today. [ About Us ]

Home  |  Forums


Copyright © 1997-2023 Yesterday's Tractor Co.

All Rights Reserved. Reproduction of any part of this website, including design and content, without written permission is strictly prohibited. Trade Marks and Trade Names contained and used in this Website are those of others, and are used in this Website in a descriptive sense to refer to the products of others. Use of this Web site constitutes acceptance of our User Agreement and Privacy Policy

TRADEMARK DISCLAIMER: Tradenames and Trademarks referred to within Yesterday's Tractor Co. products and within the Yesterday's Tractor Co. websites are the property of their respective trademark holders. None of these trademark holders are affiliated with Yesterday's Tractor Co., our products, or our website nor are we sponsored by them. John Deere and its logos are the registered trademarks of the John Deere Corporation. Agco, Agco Allis, White, Massey Ferguson and their logos are the registered trademarks of AGCO Corporation. Case, Case-IH, Farmall, International Harvester, New Holland and their logos are registered trademarks of CNH Global N.V.

Yesterday's Tractors - Antique Tractor Headquarters

Website Accessibility Policy