Correct PTO RPM to Bush Hog

[hazmat]

Uh... That's not purely coincidental. (Google "Rose-Hulman Institute")....

Don't have to - I actually spent 3 weeks there during high school for a summer program (some might call it geek week - but I prefer to call it summer camp) . Small world ehhh???

 

[Lawnjocky]

Thanks a lot guy's, now my brain hurts.

 

[greg_g]

I guess if you had said it should be adjusted to slip at a different torque for different rpm use I would disagree less. Such would give such a small advantage, considerind the ample surplus torque the clutch should provide above pto steady state output, that yould have to instrument the system to find a benefit.

Sorry Larry - I see your words, but I still can't figure out what they're supposed to mean. First you say I'm wrong because HP doesn't slip the clutch, now you say I'm wrong because RPMs don't slip the clutch. Funny thing is, I never said either. I clearly stated it takes the amount of torque specified in the chart to overcome the slipclutch spring tension at the various PTO horsepower ratings.

Best I can piece together is that maybe you'd like to see the slipclutch manufacturers base their settings charts on engine torque curves instead of a specific PTO horsepower and RPM. (I kinda think that's how JD does it already - with equipment specific slipclutches).

Anyway. Since engine horsepower and PTO horsepower are not the same, how would you then translate engine torque into PTO torque? If that's what you've got in mind, I'd envision a pretty thick slipclutch manual. Sounds like a pretty confusing "chart" to me

//greg//

 

[greg_g]

I don't see how that matters unless that tranny is attached to a rotating mass (blades, spindle, stump jumper) that is too large for the 45 hp tractor to handle. (And there is no indication that this is the case). I wouldn't think the gear box, regardless of how high it is rated, adds anything to a low velocity shock load. I'm not trying to argue, just trying to get this all sorted out in my head.

It matters, because the 120 mower tranny is supposedly constructed to take everything that 120 PTO horsepower can throw at it. One could then make the same argument for the 45hp PTO. As such, the 120hp mower tranny is going to withstand a helluva lot more shock load than will the 45hp PTO that's currently turning it. So when the 120 hp withstands a huge hit, said hit is transfered in the direction of the 45hp PTO.

Yes, the slip clutch is supposed to protect the lighter duty PTO. But that protection is premised upon an operational slipclutch that is matched to the tractor's PTO output. In the case of the Eurocardan I use as an example, that means using manufacturer settings derived from a 540 RPM model, and then actually operating it at 540 PTO rpm.

//greg//

 

[greg_g]

According to your formula as RPMs INCREASE torque DECREASES

Perhaps you should check your math Chuck. I suspect you may have confused yourself by plugging engine Torque and HP values in there. As you can see in any engine torque vs hp curve, you must consider that they BOTH change with RPMs. If you insert a HP value into that formula, you must consult the engine's torque curve to determine the associated torque value at the RPM that produces that HP number. For example, at 2600 RPM the OP L5240 engine is rated to produce 54 engine HP and 45 PTO hp at 2600 engine RPMs. Plugged into the formula, the L5240 is making about 109 pounds of torque at that point.

Works a bit different at the PTO output. Since this is a PTO discussion, I used PTO values. Remember, PTO ratings (HP) are established at 540 PTO rpms, which means how many revs the engine might be turning to obtain 540 at the PTO - is irrelevant to this particular calculation.

Since the OP question involved his L5240, let's solve for the amount of PTO Torque.
If HP = Torque*RPM/5252, then Torque = HP*5252/RPM.
RPM for his Woods 720 a fixed 540,
PTO output (HP) for his L5240 is rated at 45;
so 45*5252/540 = about 438 pounds of torque delivered by the L5840 PTO spline to the tractor side of a slipclutch.

The difference between engine HP/Torque and PTO HP/Torque is because of the transmission. After going through gear reduction, the engine HP/Torque was converted into PTO HP/Torque; HP went down, Torque went up.

//greg//

 

[Glowplug]

I'm not really trying to argue, maybe just a bit confused.
Your formula, when solving for torque is: Torque = HP*5252/RPM

Just by looking at the formula, without putting in real numbers, the bigger the number you put in the RPM variable, with all else being constant, the smaller the result of the torque. You are dividing the product of HP and the constant 5252 with RPM. So the larger the RPM the smaller the result would be.

 

[greg_g]

I'm not really trying to argue, maybe just a bit confused.
Your formula, when solving for torque is: Torque = HP*5252/RPM

Just by looking at the formula, without putting in real numbers, the bigger the number you put in the RPM variable, with all else being constant, the smaller the result of the torque. You are dividing the product of HP and the constant 5252 with RPM. So the larger the RPM the smaller the result would be.

That may be the case if you only change the RPM value. But again you missed my reference to the torque curve. Depending upon where you are on the curve for that specific device, either HP or Torque or both will change with RPMs. If you can't change the RPM value in that formula WITHOUT a corresponding change to at least one of the other values.

You have seen a torque vs horsepower curve, right ?

//greg//

 

[Glowplug]

You have seen a torque vs horsepower curve, right ?

//greg//

Yes.
But doesn't it usually decrease after you reach a certain point? After a certain RPM the horsepower starts to decrease. That's what you're talking about aren't you? A horsepower vs. rpm curve? Not really torque and horsepower.

 

[greg_g]

Yes.
But doesn't it usually decrease after you reach a certain point? After a certain RPM the horsepower starts to decrease. That's what you're talking about aren't you? A horsepower vs. rpm curve? Not really torque and horsepower.

Well, yes and no. Sometimes they're plotted together (hp vs torque), sometimes they're plotted together. Each is plotted against RPM. And no. Torque peaks, at a certain RPM then the curve typically flattens out. HP continues to increase with RPM.

This is another reason behind the argument to run the PTO at enough engine RPMs to make the recommended 540 revs. Yes, the torque curve may peak at - let's say 1700 engine rpms, at which point max torque is generally available up to the governor limit. But. From the point where torque peaks, horsepower continues to climb - usually right up to full throttle. That's how you get the reserve power by mowing/tilling/whatever at 540 instead of backing off on the throttle because of the mistaken idea that it's more economical. At 540 you're getting max torque PLUS nearly full horsepower delivered to the PTO shaft. Minimizes bogging down that way, and maintains consistent fuel consumption (governor doesn't have to ask the injection pump to constantly correct).

//greg//

 

[Glowplug]

Well, yes and no. Sometimes they're plotted together (hp vs torque), sometimes they're plotted together. Each is plotted against RPM. And no. Torque peaks, at a certain RPM then the curve typically flattens out. HP continues to increase with RPM.

This is another reason behind the argument to run the PTO at enough engine RPMs to make the recommended 540 revs. Yes, the torque curve may peak at - let's say 1700 engine rpms, at which point max torque is generally available up to the governor limit. But. From the point where torque peaks, horsepower continues to climb - usually right up to full throttle. That's how you get the reserve power by mowing/tilling/whatever at 540 instead of backing off on the throttle because of the mistaken idea that it's more economical. At 540 you're getting max torque PLUS nearly full horsepower delivered to the PTO shaft. Minimizes bogging down that way, and maintains consistent fuel consumption (governor doesn't have to ask the injection pump to constantly correct).

//greg//

I don't have anything else to say.