hydro pto hp loss?

TNCHRIS · May 19, 2004

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 @ 2250 rpm pto geared for 540 at 1740rpm for massey, Kubota 30.5hp @ 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.

_RaT_ · May 19, 2004

Well Chris, I never think about it that hard. My neighbor does use his BX type tractor with a chipper in the stationary mode. I can only say that whatever the power coming off the PTO on my L3830 HST has been plenty to operate my 84" finish mower. My tires are not filled.

Laminarman · May 19, 2004

Here's my thought: does the tractor do the job?? Question answered.

To20Chris · May 19, 2004

The issue is what is different between the two. A question I had posted on before is if the PTO is driven directly from the engine on a hydro? If the PTO is a direct mechanical link to the engine, then I don't know why the PTO power would be less with the hydro, other than maybe there is some constant drag/loss due to the hydro system? If the PTO is driven from the hydraulic system then there would be losses. It would seem the only real difference between the two systems is the hydraulic DRIVE system, and in that you will loose some drive power to pumping loss/bypass. But the PTO should not be much diffferent.

_RaT_ · May 19, 2004

"If the PTO is a direct mechanical link to the engine, then I don't know why the PTO power would be less with the hydro, other than maybe there is some constant drag/loss due to the hydro system?"

There is a loss just sitting there with hydro. A depress of the clutch especially while cold clearly illustrates this.

timb · May 20, 2004

Chris - couple of thoughts -

One thing I see is the Massey's PTO speed occurs well down from the peak engine HP rpm - compared to the Kubota which is set up for PTO rpm nearly at the peak hp number.

2nd - how many hours were on your Massey? Could it have been a little 'tired'?

3rd - since tractordata.com still seems to be down - what does a Massey 135 have under the hood? # cyls/diesel/gas - could have a very different torque rise from the Kubota.

Lastly - your are using published numbers on both - yet more than one person has listed here the results of having their personal CUT run on a dealers dyno - and it seems to me that often there's a lot more power there than the mfg.s are conservatively listing.

Add them all up and it doesn't seem impossible that the Kubota feels a little stronger than the Massey you replaced. Seems like a nice 'problem' to have.

Tim

To20Chris · May 20, 2004

This is the issue that still confuses me. My gear tractor has a hydraulic pump too, pretty much the same size and volume as a hydro. In fact, it appears that most everything is the same, with the exeption that the gearbox is replaced with a hydraulic motor. Given that, the only differences I see would be those having to do with the propulsion, i.e. the thing that is different.

The engine makes a cetain amount of power. There is a direct mechanical PTO and a hydraulic pump creating parasitic losses, same for both gear and hydro units (when stationary), so losses to the PTO output should be the same for both. If you are also driving the tractor, then the hydro will loose a few more hp (of the total made by the engine) in heating the hydaulic fluid.

So does that mean they rate the PTO hp while the tractor is moving? I always figured that it would be while stationary. I'm not even convinced THAT would limit the PTO power, just the power available to drive the tractor!

If the PTO hp rating is just the power available at the PTO while the tractor is not moving, then I still don't see a reason why the two would be different (ignoring hydraulic independent PTOs for the time being). Since all the mfg appear to list less PTO power for the hydros (?), I must still be missing something! Perhaps it is in the definition of "PTO Power"? Anyone know where the power goes on the way from the engine to the PTO with a hydro?

_RaT_ · May 20, 2004

Here's a test you can do. Have someone sit on the tractor. Start it up, clutch in, leave it in. Get down to the HST filter and put your hands around it. Release the clutch and feel how much that filter expands, you can feel it. Alot of pressure being pumped by the hydrostatic pump just sitting there. Add the two other hydraulic pumps for loader etc. and power steering. While a gear will be turning some shafts/gears in oil in the transmission, the loss is probably quite less.

To20Chris · May 20, 2004

OK - can't test that cause mine is a shuttle shift - but I'll believe you! /forums/images/graemlins/smile.gif I think you may have provided the part I'm missing - is there a separate pump for the hydrostatic drive? I figured they would just use one pump, the same one used for the lifts, etc. If that is the case, then the additional losses must come from driving the additional pump, even when it is not moving the tractor. I just like to understand how it works!

Moon · May 20, 2004

Chris,
A year or two ago, there was a discussion on HST and how it works. Lots of good info. Diagrams and everything. Maybe that would help explain the hp loss.
Moon of Ohio