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Farmall & IHC Tractors Discussion Forum
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tractor detail,s

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kirk ,in ks,

05-23-2006 07:01:50




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I dont get the difference between pto powewr and drawbar power?
My W-6 say,s 44 hp on the pto,on the tractor data page,and 32 or 33 on the drawbar type,
i dont get it,




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chadd

05-23-2006 07:52:59




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 Re: tractor detail,s in reply to kirk ,in ks,, 05-23-2006 07:01:50  
PTO horsepower is measured by hooking a dyno up to the PTO shaft and then using hydraulic pressure to place load on the engine. As a larger load is applied, the governor will continue to feed more fuel in to the engine so that it will maintain the PTO speed at 540 rpm. When the load is just high enough that the governor can just barely keep the engine speed fast enough to keep the PTO speed at 540 rpm(i.e the throttle plate is as close to vertical as the governor will let it go), that is the max PTO horsepower. Drawbar horsepower is just what it sounds like. It is a water brake hooked to a carriage that provides variable resistance to a tractor pulling it with its drawbar. Because pulling always involves some slippage and power loss, and involves moving the weight of the tractor its self, it will always be lower than what you get at the PTO. That is the way I understand it to be, although, I am sure someone else will be able to give you a more accurate answer.

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Bob

05-23-2006 07:40:56




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 Re: tractor detail,s in reply to kirk ,in ks,, 05-23-2006 07:01:50  
It's simple... there is power lost in the transmission gears and bearings, and to tire flex and wheel slip!

So, drawbar HP is the actual work the tractor is able to do, with those losses figured in.



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Bob M

05-23-2006 07:40:04




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 Re: tractor detail,s in reply to kirk ,in ks,, 05-23-2006 07:01:50  
PTO horsepower is essentially the tractor engine's HP available at the flywheel less a small amount for the gearing and friction losses ocurring in the PTO transmission.

OTOH drawbar HP is the HP available at the drawbar to do pull-type work. Ie. it's flywheel HP less the power required to move the tractor over the ground.

As you observe these losses can be 20% - 25% or more of the total horsepower. Losses vary somewhat depending on the weight of the tractor, type of tires, degree of tire slippage, type of surface (ie. amount of soil compaction from the rolling wheels), etc.

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