HST/ PTO SPEED

[J_J]

Note that Kubota went to net hp marketing a while back. Your L3130
has 31 net hp, while gross is 32.1hp. Most tractor makers don't do
it that way....kudos to Kubota.

BTW, your tractor makes 25.5hp at the PTO, unless you have a HST;
then its only 24hp. 1.5hp is to run the charge pump.

He has an L3240

 

[First one]

The real hp numbers you should compare are either drawbar or PTO hp depending on what you will be doing with the machine.

When looking around for a tractor,I think some newbies look at the engine hp(gross) ,but what i've picked up on here is that it's the pto speed /and weight of the tractor(traction) 4x4 or2x4.
That's what's going to make the difference in how much you're going to be able to work your tractor to its potential. I can see now how loaded tires, the type of tire you have and with or without chains is as important as the hp of the tractor , right?

 

[beppington]

The real hp numbers you should compare are either drawbar or PTO hp depending on what you will be doing with the machine.

When looking around for a tractor,I think some newbies look at the engine hp(gross) ,but what i've picked up on here is that it's the pto speed /and weight of the tractor(traction) 4x4 or2x4.
That's what's going to make the difference in how much you're going to be able to work your tractor to its potential. I can see now how loaded tires, the type of tire you have and with or without chains is as important as the hp of the tractor , right?

I said to my dad while pulling trees out, one of which was just too big to pull, "Guess more horsepower wouldn't even work for this, since traction is the problem." He said, "True, more horsepower would mostly help with the PTO."

 

[Ford tractor]

I can see now how loaded tires, the type of tire you have and with or without chains is as important as the hp of the tractor , right?

Exactly. But don't forget the weight. Some modern tractors with 30hp are VERY light, much lighter than an old tyme 20hp machine.

I said to my dad while pulling trees out, one of which was just too big to pull, "Guess more horsepower wouldn't even work for this, since traction is the problem." He said, "True, more horsepower would mostly help with the PTO."

Yep, dad's right (again!).

Once you have enough hp to force the tires to slip, adding more is not going to gain much if any. Adding weight will allow you to pull more and be more stable doing it. Most new folks underestimate the additional stability gained from adding fill to tires.

If you analyze it objectively, those old timer really knew what they were doing.

 

[hawkeye08]

Sadly, you are close but not all the way there.

Gross hp is how much the engine makes, typically with no alternator, intake filter or muffler. Just the engine, best case. Net hp is what the engine makes as it sits in the tractor. It's not useable as it has to go through a transmission/differential or hydraulic pump before it can be used. PTO hp is the amount you can use at the pto (obviously!). It's about 5-8hp less than the net and 7-10 less than the gross and is impacted by drive line losses. Drawbar hp is the amount of pulling work you can do. It's impacted by both driveline losses and geometry / traction. It may be a bit more or less than PTO hp depending on the machine. A heavier machine will have better traction and more drawbar hp than a lighter machine with the identical engine.

The real hp numbers you should compare are either drawbar or PTO hp depending on what you will be doing with the machine.

So the better statement is that Gross HP is what they charge you for, but PTO (or drawbar) hp is what you buy.

You are entitled to your opinion of course, I chose to define it one way, you chose another. You are close, but you missed since my tractor actually has to use that transmission and I count that as part of the work being done. It doesn't really do me much good to be able to run my RFM (because of pto hp) and just sit in one spot. In addition to the net HP number that I buy the tractor with, I also knew the pto hp so I knew what I had to run pto driven implements (yes, I know that is at the pto rated rpms and that it is the max).

I also have the weight I want to maximize traction and take advantage of the hp I bought.

 

[Redneck in training]

The difference between maximum HP and PTO HP has something to do with power curve of the engine. Example: Engine is rated 33HP at 2900 rpm but has only 31.5 HP at 2500 rpm PTO speed. Another thing to notice is that the engine will have the lowest specific fuel consumption [gal/hour/HP] at the maximum torque.

 

[JoeL4330]

The advertised PTO HP is at the RPM setting that makes 540 rpm at the PTO.

If you keep the RPM at that setting, the PTO makes that much horsepower no matter what else the tractor is doing...read the previous sentence carefully. If something you do causes the engine to bog down (i.e., lower the RPM) then the HP at the PTO will decline.

On my HST a setting of ~2500 engine rpm makes 540 PTO rpm ...and this is true for most diesel compacts ...indeed, the PTO gearing is set up to make this so. Why is that? if you look at the torque curve for diesel from the previous post, you see that this is just beyond the torque peak ...on the backside of the torque peak, as it were. Why is that? Well, if your engine sees a sudden load and starts to bog, the rpms drop and the torque actually increases (for a bit) which may enable you to ride through the temporary excess load (pretty smart, them engineers).

Indeed, my tractor has a digital tach for the PTO and I can see it rise as, say, I go downhill, and drop slightly as I go up a steep hill ...but, when it is at 540 (which might require a throttle adjustment, up or down the hill) then the PTO makes its rated HP.

If I try to climb a very, very steep hill, throttle may not be sufficient to maintain 2500 engine rpm (and therefore 540 PTO rpm) and I have to shift into low range on my HST.

 

[patrick_g]

Just in case some one takes any loosely/poorly worded post at face value...

Just because the PTO shaft is spinning at 540 RPM and your tractor is rated at "umpty squat" PTO horse power that does not mean the PTO is delivering any horse power because it is not doing any work.

Kudos to those whose explanations mentioned HP as being the result of torque and RPM. RPM with no torque does not provide horse power.

Patrick

 

[Ford tractor]

You are entitled to your opinion of course, I chose to define it one way, you chose another. You are close, but you missed since my tractor actually has to use that transmission and I count that as part of the work being done. It doesn't really do me much good to be able to run my RFM (because of pto hp) and just sit in one spot. In addition to the net HP number that I buy the tractor with, I also knew the pto hp so I knew what I had to run pto driven implements (yes, I know that is at the pto rated rpms and that it is the max).

I also have the weight I want to maximize traction and take advantage of the hp I bought.

??

My understanding is that when the PTO is using maximum hp at the rated rpm, there is NO left over hp sitting around in reserve for other uses. The power used to move the tractor or run some hydraulic device is subtracted from the PTO power. Bog the PTO and the ground speed drops, go up a steep hill or snag a stump and the PTO slows.

 

[johnrex62]

Just in case some one takes any loosely/poorly worded post at face value...

Just because the PTO shaft is spinning at 540 RPM and your tractor is rated at "umpty squat" PTO horse power that does not mean the PTO is delivering any horse power because it is not doing any work.

Kudos to those whose explanations mentioned HP as being the result of torque and RPM. RPM with no torque does not provide horse power.

Patrick

I think you are quite correct that without load the HP is not being utilized and thus is not present, but the capacity of the engine and the PTO are still there even without a load or application of torque so I think the HP is still available.

If you can demonstrate how an unloaded PTO operating at 540RPM loses it's ability to apply torque to a load if it were present just because there is no load currently applied, then I will consider this technicality relevant to the OP's question.

Otherwise, I think the correct answer to his question is better answered by the machine's ability to deliver HP rather than the specific HP being converted to the workload being undertaken.