HST question

[Bob_Young]

When operating a PTO powered implement, such as a mower, where engine RPM is kept fairly high and assuming the same ground speed in each case; which will result in lowest HST temperatures:
1)Operating in low range with the pedal floored
2)Operating in high range with the pedal slightly depressed.

I suspect the answer is 1) due to higher flow rate; but I'm a gear head so what do I know?
Bob

 

[BillyP]

You are correct, Sir

 

[thcri]

Bob,

I would agree with you for the most part. An example where I might think different would be if your mowing on flat land, there is a load on the PTO but really no load on the hydro, then I think you could use the higher range and still be ok as not much heat would be produced in the tranny. Now if you were pulling something very heavy then you have a good point.

It is a good question and I hope others chime in here on this one.


murph

 

[PineRidge]

I would think that throttling the hydraulic flow creates more heat than if you were running with the pedal down. Not sure though as I'm no transmission expert.

 

[texasjohn]

I've been toying with getting a thermometer like a buddy of mine has... point a laser and it takes the temperature of the location.... Harbor Freight has them for $40 but haven't justified that expense yet.... If anyone has such an instrument, then it would seem possible to run a test, take the temp and rerun the test... several times to see what the results actually are... just an idea.

 

[jinman]

When operating a PTO powered implement, such as a mower, where engine RPM is kept fairly high and assuming the same ground speed in each case; which will result in lowest HST temperatures:
1)Operating in low range with the pedal floored
2)Operating in high range with the pedal slightly depressed.

I suspect the answer is 1) due to higher flow rate; but I'm a gear head so what do I know?
Bob

Since this is a good "theoretical" question, I'm going to say that in theory there will be no difference whatsoever; the heat sources offset each other.

1. The increased flow will have more friction and create heat.
2. The increased pressure will create heat.

As long as you don't waste energy by lifting the HST pressure relief bypass valve, I think the difference would be insignificant.

 

[JimR]

There is more strain in high gear than in low gear on a HST when trying to go slow. You are better off in low or second speed with the peddle down. I mow in second on mine with my 6' MMM and the peddle to the metal. In high gear I would have to lug it up the inclines.