WOT on diesel tractors

[TomSeller]

Just because an implement has a speed rating of 540 rpm doesn't mean it is necessary to run it at that speed. More at the speed rating should be considered the maximum speed. Some things such as finish mowers will do a better job at the rated speeds but others can work at a slower speed without issues tillers, post hole diggers and harley rakes. But if you take that same implement and hook it to a 1000 rpm or 2000 rpm pto it may fly apart. Some things such as ac gensets need to be run at rated speed even with light loads but others such as a dump truck hydraulic lift will work at low idle or fast idle.

Well said. Sysop's post was as well. I agree, if it is a cutting attachment or maybe a baler, you may need certain PTO speeds, but many attachment's required speeds are dependent on the use. I don't 2-position my throttles, I use the full range.

 

[yelbike]

Well said. Sysop's post was as well. I agree, if it is a cutting attachment or maybe a baler, you may need certain PTO speeds, but many attachment's required speeds are dependent on the use. I don't 2-position my throttles, I use the full range.

2 position! Lol..... Deere could have saved money and installed a selector switch instead of a throttle assembly. I don't really under stand the purpose of this tread. I personally run my tractor half throttle for most tasks, full for tilling and sometimes mowing.

 

[arlen4720]

2 position! Lol..... Deere could have saved money and installed a selector switch instead of a throttle assembly. I don't really under stand the purpose of this tread. I personally run my tractor half throttle for most tasks, full for tilling and sometimes mowing.

Yeah, look at all the people that wasted money on that ePTO.:laughing:

 

[yelbike]

Yeah, look at all the people that wasted money on that ePTO.:laughing:

I don't know what epto is. I think its on larger tractors than mine.

 

[SPYDERLK]

Fraid not. ... Hydraulic pumps leak internally somewhat. Amt of leakage is related to pressure and time. Higher revs allow less time to leak per revolution. Therefore delivery per revolution is greater at higher rpm. This becomes more pronounced as the hyd fluid thins with heat.
larry

Increased pressure would also increase the amount of leakage too, so it could cancel out at least some of the shorter time available to leak.

Unless somebody has tested a theory like this, or has access to actual data, I'm not buying it....or at least not buying that it makes a functional difference. The pumps have a bypass...as soon as the bypass starts to open, none of this stuff really matters, because the pump is already putting out full pressure, and volume.

Actual use of your machine can give you an idea when the bypass engages....anything above the RPM at which you see full lift, and the shortest cycle times. If increasing RPM doesn't decrease the cycle times, or increase the lifting ability, your pump is already putting out full pressure, and volume, and the bypass is engaging to prevent any additional increase.

I dont see that you addressed the quote, which you seem intent on contradicting by repeating the info in it. I spoke of internal leakage only. You then seem to introduce and mix in relief pressure which is different and totally unrelated.
larry

 

[SPYDERLK]

Originally Posted by JDTank
For tractors with hydrostatic transmission, the pumps are designed VERY SPECIFICALLY to run at their rated RPM input speed, which is full throttle.

Originally Posted by JDTank

Tractors with gear transmissions and a controllable throttle are a different story, to some degree. While the drive-train is not controlled with hydro fluid, your hydraulic pump powering your loader, power steering, 3 pt arms, all of that stuff, is still suffering the same fate. The higher the RPM, the easier it is for your pump(s) to do their job. In turn, they will last longer.

That is a load of ****. I think what you are saying is that hydrostatic transmissions require sufficient "charge" pressure and flow to operate properly. That sures the **** ain't full throttle.
Run the RPM's up to the point the tranny is not "sqawling" and you have enough charge pressure.


The gear pumps don't care about the RPM, they just move so much oil per rev. What isn't used bypasses back to tank. More RPM's are more wear not less.

Don't get me wrong...there is nothing "wrong" with runnig at full throttle, I'm just saying use the amount of power and RPM's you need for the job at hand.

Fraid not. ... Hydraulic pumps leak internally somewhat. Amt of leakage is related to pressure and time. Higher revs allow less time to leak per revolution. Therefore delivery per revolution is greater at higher rpm. This becomes more pronounced as the hyd fluid thins with heat.
larry

Yes, There is internal leakage of all pumps, I'm not sure what you are trying to say here. Gear pumps are a "fixed displacement" pump, they are nameplated for a certain amount of fluid per revolution. There is leakage, and that leakage increases with wear. So what? If you are saying that if you need more flow, then you should run the pump faster, then I say "no ****".
What my original point was...spinning the pump faster doesn't reduce wear...it increases it. Often less flow is desirable, and gives smoother more controllable hydraulic motion. JdTank is saying that it's all designed to run at WOT and your machine will be damaged and/or experience more wear if you don't. That is pure BS.

You said a pump delivers a specific amount of fluid per revolution. I said, correctly, that it does not. And thats all I said.
larry

 

[smilinjak]

He found it! :laughing::laughing::laughing:

Tailgating would be reduced considerably and parking could be less challenging.:laughing:
Smikinjak:thumbsup:

 

[arlen4720]

You said a pump delivers a specific amount of fluid per revolution. I said, correctly, that it does not. And thats all I said.
larry

OK, you win...I guess I didn't feel the need to talk about the volumetric efficiency of the gear pump to make my point. It wasn't part of the discussion. So I was confused by your comments on how it related to the subject at hand.
I do feel that for these types of "******" threads, you have to draw the line somewhere with how far you want to take the technical details, for example, should I have included the compressabilty of the fluid, the accumulator effect of the hoses, and possible reasonance? what about laminar and non laminar flows?
It doesn't mean a **** thing when it comes to refuting some dumb *** trying to say that you need to run your tractor at WOT all the time.

 

[GManBart]

I dont see that you addressed the quote, which you seem intent on contradicting by repeating the info in it. I spoke of internal leakage only. You then seem to introduce and mix in relief pressure which is different and totally unrelated.
larry

I addressed the quote. You singled out time, but there are two variables. At lower RPM you have lower pressure, and more time. At higher RPM, you have higher pressure, and less time. Total leakage per rev could be identical in those two scenarios, but the only way to know would be testing the exact configurations over the operating range. For your theory to be an absolute, the pressure would have to be constant....we don't know that it is. You simply can't make an accurate blanket statement that less time equals less leakage.

The relief pressure comment was when I said that minutia such as internal leakage doesn't matter in the real world....the pump typically puts out full pressure, and volume, before WOT, so delivery per revolution isn't always higher at higher RPM settings. So, there isn't necessarily a need to run at WOT.

 

[buickanddeere]

Not matter what the instance. Lugging and and in particular extended lugging is not smart with any engine. I've seen goofs running the engine all day below peak torque rpms, with the fuel rack at 100% performing heavy tillage etc.
They just don't "get it" that operating at peak cylinder pressure and near peak torque causes more stress and wear.Vs. operating at near peak HP rpms and running 80-90% of max fuel rack. Then again these guys don't have so much as a single credit in basic high school physics either.
Running at reduced rpms also reduces alternator output and reduced cooling system efficiency.
Before anybody gets their knickers in a twist. Raking hay, loader shuttle work loading bales or a 125HP 1000rpm tractor throttled back to 540rpm on a 25KW generator are another category of usage.
A hydrostatic transmission equipment machine is an example of 200rpm more than what is really required is better than 200rpm less than what is required.