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 05-19-2004, 19:27 Post: 86391
TNCHRIS



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 hydro pto hp loss


Lets think this thing over. I will use Kubota L30 series only because i can't find any other specs to really compare.

1. Pto hp is rated at engine peak speed of 2700 rpm not at 540 rpm pto. Kubota hst pto is at 2640 rpm, gear is 2550 rpm. looking at engine torque/hp charts it appears that the pto hp at 540 rpm is the same with both tractors.

2. Pto ratings are with the tractor parked. Not many of us run a sawmill or hammermill anymore. So the actual hp at the pto is "engine hp - hp used to move tractor =pto hp"
2A. Using this factor then a tractor with tires not loaded will have more pto power than one with them filled. How much hp requied to move 1000 LBS of fluid?
2A1. Two ways to gain pto hp, diet, and never fill the fuel tank over 25% eather way you reduce hp required to move the tractor.
Taking this into account is a hydro really sacraficing hp? By varing your speed ever so slightly to maintain pto speed under load, your increasing hp going to the pto.

I bought a L3830Hst thinking i was lossing pto hp from the 135 Massey I had, 37hp at 2250 rpm pto geared for 540 at 1740rpm for massey, Kubota 30.5hp at 2700 rpm geared for 540 at 2640. Can't find charts for the Massey but i'm sure hp at 540 is less than the Kubota. These old tractors also had a belt speed mark on tach at max rpm and is where pto was rated for use as a stationary power unit. The 3430 is probally a closer match to the 135 Massey, so i really got a bigger tractor, just don't look at the specs read the charts.

What do you all think? Is this correct or am i way off base.






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 05-19-2004, 19:37 Post: 86392
kwschumm



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 hydro pto hp loss

I think it would be more like "engine hp - hp used to move tractor - hp lost to waste heat - pumping losses = pto hp". Since hydros have more pumping losses and generate more waste heat those losses have to be accounted for. By the way, I like your logical thought process.






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 05-19-2004, 19:46 Post: 86393
kwschumm



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 hydro pto hp loss

Ya know, it seems to me as if speed should get factored in there somewhere. A geared machine going, say 8 mph and an otherwise identical hydro going 4 mph may end up having the same pto.

Edit: On second thought this should be covered by the "hp used to move tractor" term.






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 05-19-2004, 21:46 Post: 86403
beagle

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 hydro pto hp loss

The anount of WORK a machine can accomplish is measured By force x distance, or foot lbs. This work can be stated as torque. POWER is the speed at which work can be done, horsepower is a unit of power. In theory, and without factoring in all the losses, a 5hp machine can accomplish the same work as a 20hp machine, but would take four times as long. The increase in losses makes this impractical.

Maximum torque, or available work, usually peeks in a diesel at about 70% maximum RPM. As RPM's increase, work can be accomplished faster, but the torque falls off due to losses and inefficiencies in the engine. Horsepower begins to fall off as available torque falls faster than engine rpms are increased. At some point on the performance curve, torque and horsepower cross at peak operating efficiency, which is usually below maximum engine horsepower.

The purpose of this babling is that published horsepowers can be a little misleading, depending on how they are derived. A few things are givens; 1)A hydrostat will have less power avavilable at the PTO, and also less brake HP, due to the losses in the hydrostat. Heat is power, and for every BTU of heat built up in the hydrostat, power is lost from the engine. There is also a hydraulic loss in the hydrostat that the surge pump replaces. 2)Torque and power are only directly related at the point of the performace curve where the two cross due to losses and inefficiencies in the engine. 3)Different manufacturers post estimated HP at rated RPMs at different points on the engine perforamce curve. The gearing of the pto can fall at different points on the curve. 4)The lower the rpms are for a rated horsepower, the more efficient the engine.

Not sure any of this helps, but because HP is time dependant , it can be misleading.






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 05-20-2004, 12:07 Post: 86453
Murf

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 hydro pto hp loss

The other thing to note in all of this theoretical rambling is that there is a variable here also.

A HST has a variable efficiency rating, generally they are far more efficient at slower travel speeds.

This would mean that the same HST-equipped CUT would have more PTO hp. available for tasks like roto-tilling, than they would for cutting flat, smooth areas of turf at higher speeds. Even more power would be available for tasks like running a PTO-powered chipper since the HST would not be working at all.

Best of luck.






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 05-21-2004, 08:40 Post: 86498
Art White



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 hydro pto hp loss

For the question and the answers given here to a degree they are right and yet wrong. There is only one testing that might give back only part of the answer. Many of the farm tractors today are again introducing hydro's because of the ability to consistantly drive a machine at it's optimum pto speed as well as desired ground speed. The only place a hydro hurts and with the additional ranges being installed in tractors that difference is shrinking for pulling heavy ground engaging attachments. That said the hydro's still rule for being able to start larger loads then a gear drive tractor.






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