Flail mower PTO RPM - margin of power

PxP · Dec 12, 2016

Hello.
I want to buy Perfect BKM-150 flail mower and use it mounted frontally with my New Holland T4050N.
That flail mover requires tractor to have 40HP and my NH has more than 2x of it - 97HP
BKM-150 has 3 gearboxes to choose from when buying - 540/750/1000 RPM.
Tractor front PTO has only 1000 RPM mode, but my idea is to select 540 RPM mower gearbox.
With such margin of HP, my tracor with only 540 RPM (actual) on frontal PTO - will still have
more than needed 40HP for BKM-150 (abt. 1300 RPM on engine actual - /2300 RPM is maximum/)
Additionally with 540 RPM gearbox - it will be easy for me to use it with my older,
weaker tractors (40HP-50HP) that have only 540 PTO RPM at back.
Of course that`s theory.What do You think - will it actually work?

buickanddeere · Dec 12, 2016

No and why would you? What are you trying to save ? The task is a few hours clipping grass not operating 24/7 for months at a time powering an irrigation pump,base load electrical generation or marine propulsion. The 750 would be do able but now the mower is an orphan .

PxP · Dec 12, 2016

buickanddeere said:
No and why would you? What are you trying to save ? The task is a few hours clipping grass not operating 24/7 for months at a time powering an irrigation pump,base load electrical generation or marine propulsion. The 750 would be do able but now the mower is an orphan .

Actually clipping not grass only, but branches from orchard winter/summer prunning. Not few hours, but quite opposite - about 60 hectares of orchards - so more than 200km of driving and mowing branches at least 2 times per year + grass mowing 3-4 times(more than 1000km a year).
So then - will 540 RPM gearbox be OK or not?

Regards.

buickanddeere · Dec 12, 2016

Not. Tractor will be lugging with boggy throttle response. We regularly have people here who want to operate a 540 rpm pto generator on a throttled back 1000rpm tractor. Unless the tractor is more than 3X over size and better 4+ times over size . The tractor boggs and can't maintain rpm when starting motors etc.

vlcakc · Dec 12, 2016

If I understand what you propose correctly, the flail rotor speed would only be slightly more than half the designed rpm. Very likely much too slow to get a satisfactory cut when mowing. Vic

buickanddeere · Dec 13, 2016

vlcakc said:
If I understand what you propose correctly, the flail rotor speed would only be slightly more than half the designed rpm. Very likely much too slow to get a satisfactory cut when mowing. Vic

Flail speed will be rated rpm. Depending on the gear Box the tractor engine rpm will be at rated, 2/3 or 1/2 of rated engine rpms.

sdef · Dec 13, 2016

No clue, but am interested in why you want to use a flail on the front instead of the rear which is more of the standard and more flexible with other tractor usage? I seldom run a flail at full PTO 540 RPM anyway. Mine runs fine a few hundred RPM less at the tractor unless I need to mow very dense, wet and heavy stuff and uses the heavier hammer blades.

Industrial Toys · Dec 13, 2016

Does it rotate the right way? Can't tell you how many people have run into that snag.

I wouldn't do it. I run a little 917 Ford with a 70 HP JD. A little overkill but who cares?

I also might be worried about the potential to overspeed the mower. Maybe not you but someone else.

I never even noticed that it is a perfect mower. I have such a ditch bank mower. Maybe ten pound hammers. Terrible for stones as you can't repair the hammers, but it's good quality equipment.

Industrial Toys · Dec 13, 2016

Picture of my "PERFECT" Baby, just after I got it, before sandblasting, repairing and paint.

View attachment 491404

Xfaxman · Dec 13, 2016

It might work if your tractor had a hydrostatic transmission.

I have no experience with the Power Shuttle:

PxP · Dec 13, 2016

My decision what to buy/select on hold now.
Drove with my tractor to nearby New Holland dealer - they have also KUHN flail mowers - similar to one I want buy.
Wanted to check if it will work - 540 gearbox>1000 PTO.
It turned out my tractor front PTO is damaged (I never used it earlier - tho my tractor is 4 yrs old) :-(
When it will be fixed - I`ll check.

Xfaxman · Dec 13, 2016

sdef said:
No clue, but am interested in why you want to use a flail on the front instead of the rear which is more of the standard and more flexible with other tractor usage?
----------------

Since he didn't answer, my guess is he is mowing a vineyard or orchard, since it is a narrow tractor.

My other guess is that you have never mowed with a machine with an out front deck:

Industrial Toys · Dec 13, 2016

I saw a Kuhn at a friends place. It looked identical to my Perfect mower. I was going to look into it further next time I need knives/hammers.

Knives and hammers I can get anytime, but other stuff gets ordered from Europe once a year in a container.

PxP · Dec 14, 2016

>I am interested in why you want to use a flail on the front instead of the rear which is more of the standard and more flexible with other tractor usage?

When chopping branches from winter/summer pruning in orchard with flail mower at back - it quite often happens that apple tree branches pierce tires.
No such problem when flail mower at front.

Regards.

PxP · Dec 14, 2016

Tried today KUHN flail shredder BKE 180 REV with New Holland tractor (75HP) - mounted at front.
It worked ok - chopping 2-3 cm dia. branches. I`ve driven quite slow though.
Worked with 75HP - will work with 100HP.

Regards.

SPYDERLK · Dec 14, 2016

PxP said:
My decision what to buy/select on hold now.
Drove with my tractor to nearby New Holland dealer - they have also KUHN flail mowers - similar to one I want buy.
Wanted to check if it will work - 540 gearbox>1000 PTO.
It turned out my tractor front PTO is damaged (I never used it earlier - tho my tractor is 4 yrs old) :-(
When it will be fixed - I`ll check.

... OK, on hold
,,,,,,Re your orig question/decision point - At 1/2 rated rpm your tractor puts out less than half its rated HP. If torque stayed constant as rpm dropped you would have 1/4 the rated hp at half the rated rpm speed. -- BUT, torque of our diesels is not quite constant and maxes out well below power peak. From power peak, it rises slowly as rpm drops. The peak T is usually around 1700 rpm. Thats the sweet spot you want to be near. With 540 @ 1300 youre essentially falling off the bottom, and 25% of peak power is probably about right.

The 750 RPM implement gearbox should work nicely for your 1000 RPM PTO situation on the big engine. --- But wont be so good for the little tractors. :confused3:

sdef · Dec 14, 2016

Xfaxman said:
Since he didn't answer, my guess is he is mowing a vineyard or orchard, since it is a narrow tractor.
My other guess is that you have never mowed with a machine with an out front deck.

Yes, you are correct. I do understand the virtues of the mower type you posted. However, a 97 HP tractor is a different piece of equipment altogether. I have never performed large scale mowing requiring a 97 HP tractor with a front mounted mower, which is why I asked for specifics. My mind is still searching for the type of operation requiring something like this or how a front mount would be better than a rear mount on a tractor such as this with the PTO RPM mentioned and mower speed modification required. Just a learning experience for me.

Or maybe the OP just wants what he wants, which I can certainly relate to as I do similar sometimes

.

motownbrowne · Dec 14, 2016

sdef said:
Yes, you are correct. I do understand the virtues of the mower type you posted. However, a 97 HP tractor is a different piece of equipment altogether. I have never performed large scale mowing requiring a 97 HP tractor with a front mounted mower, which is why I asked for specifics. My mind is still searching for the type of operation requiring something like this or how a front mount would be better than a rear mount on a tractor such as this with the PTO RPM mentioned and mower speed modification required. Just a learning experience for me.

Or maybe the OP just wants what he wants, which I can certainly relate to as I do similar sometimes .

Makes perfect sense to me. He's mowing/mulching prunings from orchards. Material like that sucks to drive over. It gets tangled up under tractors and ends up tearing off hydraulic lines, etc. By mowing before driving over the material you eliminate that problem. You clear yourself a path so to speak.

To the OP, personally, I'd much rather run the tractor at higher RPMs. That's what it's made for. That's where the HP is, that's where the oil flow and coolant flow is optimized for long term use.

PxP · Dec 14, 2016

SPYDERLK said:
... OK, on hold
,,,,,,Re your orig question/decision point - At 1/2 rated rpm your tractor puts out less than half its rated HP. If torque stayed constant as rpm dropped you would have 1/4 the rated hp at half the rated rpm speed. -- BUT, torque of our diesels is not quite constant and maxes out well below power peak. From power peak, it rises slowly as rpm drops. The peak T is usually around 1700 rpm. Thats the sweet spot you want to be near. With 540 @ 1300 youre essentially falling off the bottom, and 25% of peak power is probably about right.

The 750 RPM implement gearbox should work nicely for your 1000 RPM PTO situation on the big engine. --- But wont be so good for the little tractors. :confused3:

Actually peak torgue in my NH is at... 1300 RPM - same RPMs as I want to work combined with flail chopper 1000@540 RPM PTO.
Max. torque ISO TR14396 (Nm@rpm) - 398@1300
Rated engine speed (rpm) - 2300

As I wrote earier - 75HP tractor worked ok 1000@540 RPM PTO with KUHN flail chopper. My NH got 25% more power and better torq. at lower engine RPM.

Flail mower I want to buy and front/back config. of it: