Mid PTO use?: John Deere Review  -- John Deere Tractors Discussion Forum and Review Mid PTO use?: John Deere Review -- John Deere Tractors Discussion Forum

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 03-19-2004, 04:35 Post: 80371
hardwood

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 Mid PTO use?

I'd like to mount a 30 GPM hydraulic pump under my 4410 driven by the mid PTO to power a 42 inch light duty rotary mower on an offset frame mounted on the 3pt. to be able to drive in the bottom of the road ditch and mow the steep incline while keeping the tractor level, kind of a mini version of the big units the county uses. My question is, does the smaller 2100 RPM mid PTO have the ability to handle the full power of the engine like the rear PTO, or was it meant only for light to medium duty use. I've tried to figure ways of using the rear PTO thru a 90 degree gearbox but that gets pretty complicaed, so for the sake of simplicity I'd like to use a hydraulic drive. Thanks, Frank.






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 03-19-2004, 05:39 Post: 80373
harvey



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 Mid PTO use?

Frank I have looked at that idea many times, only for another purpose.

I can not see any problem with power. If it were me, I'd try to size the pump input shaft close to the pto size.

I think, (WAG) (wild ass guess) the pump would be expensive.

A 72" mid mount mower has gotta be using all avaiable power.

I need to get with the local guy at the hyd shop and prusue that idea.






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 03-19-2004, 05:45 Post: 80374
blizzard



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 Mid PTO use?

The mid PTO must be able to handle the full engine power, otherwise it would break if you ever plugged the mower with heavy grass. Torque would be a lot less than the 540 RPM rear PTO, and some mfgs. use a special shaft spline.


Here's the formula: HP = (Torque * RPM) / 5252


or, Torque = (Horsepower * 5252) / RPM

Hope this helps,
bliz

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 03-19-2004, 07:55 Post: 80385
Murf

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 Mid PTO use?

Frank, it will handle the load...however, you have to be careful.

Many PTO's are suseptable to bearing problems if you load them up at less than rated PTO speed. Same applies to transmissions, they are designed to run ground-engaging implements (plows, etc.) at about 5 mph.

I remember reading a study done by one of the big Ag. universities in conjunction with I believe Case. They found that the tx would only last half as long if you worked it hard at the wrong speed.

I also remember seeing a CUT in pieces at the dealers a few years back, the owner had been cutting a lot of grass with it, but instead of using the right speed and 540rpm setting, he was running much slower and using the 1,000rpm setting. Every bearing in the PTO line was shot and a few in the tx itself.

Usually the mid-PTO runs hat a higher speed than a pump wants to run. It's probably easier (and safer) to just buy a Prince PTO pump at TSC, they're only a few hundred bucks and will run ANYTHING.

And don't forget, you will need a BIG reservoir to keep all that work from making more heat than the system can handle.

Best of luck.






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 03-19-2004, 11:26 Post: 80397
Murf

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 Mid PTO use?

The other problem will be weight.

Even a light duty Howse (42"Wink yeah right cutter will weigh about 500 lbs. and if it is offset to run on the outside of the rear tires then the mid-point of the weight will be, half the width of the tractor, 30" ?, plus half the width of the cutter as hitched, 21", 51" beyond the centerline of the tractor. This will require some serious counter-balance weights a LONG way out the other side in order to be able to safely pick it up.

I would think an old sickle-bar mower would be a whole lot easier and safer.

Best of luck.






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 03-19-2004, 17:35 Post: 80421
beagle

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 Mid PTO use?

I like blizzards line of thought. The mid pto will develop 1/4 the torque of the rear pto. This will work the engine hard. I swore to never use a mid mount mower deck again for just that reason. It loads the engine harder than most anything off the rear. Use the rear pto to run the hydraulic pump for good torque at the proper rpm.

Thse sickle mowers look a little dangerous to me, but that is probably because I lopped the ends off two fingers a couple years ago with hedge trimmers. They look like big hedge trimmers to me.






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 03-20-2004, 05:06 Post: 80456
hardwood

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 Mid PTO use?

Thanks to everyone for all your input. The rear mounted offset rotary mower was one of those 2 o'clock in the morning strokes of genius that we all seem to have now and then. I allready have the pump, universal joint shaft, some of the mounting brackets built to put the pump under the 4410. The original idea of the pump unit was to power orbit motors on grain augers during harvest. We did kind of the same thing to an "M" Farmall a couple years ago, by mounting a pump under the tractor and powering it from a double v pulley mounted on the original belt pulley hub of the "M" and using the rear end housing as a sump. After some fine tuning it has worked out real well. The pump unit for the 4410 will be totaly independent of the tractor, separate sump, it's own valve unit, and possibly a radiator unit if heat becomes a problem. I normaly order pumps, valve units, orbit motors, etc. from The Surplus Center. They have a good tech. dept. that will help you size pumps, motors, valve units, or whatever you need to match what you want to acomplish. You've answered my question of the ability of the PTO to handle the load, and brought up a lot of good points on the problems I would run into with weight being off centered, etc. After doing some calculating it looked like even with a light duty mower, (the one I checked on weighed 440 lbs.), the 3pt. frame to mount all this to, quite a bit of counterballance weight I was going to end up in the 1500 lb. range, that seems pretty heavy. I called around checking the price of a light mower and with the most recent 9% price rise, things got out of hand pretty fast. I do have a couple sickle mowers out in my "Reserve Inventory Yard", my wife has another name for it something like "that blankety blank junk yard" so the old sickle mowere are starting to look better right along. Thanks again, Frank.






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 03-20-2004, 06:38 Post: 80461
TomG

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 Mid PTO use?

For a pump the shaft, direction of rotation, max pressure, displacement and rpm range are important. I think max rpm's may run up to 4000 rpm but typical operation is under 2000 rpm. Might be that a pump could be found that wouldn't require gearing. The flow/pressure requirements of the load would determine the pump displacement and pressure rating and also the pto output hp required. Well, payment for losses has to be thrown in.

I'll do a take on some concepts, or at least my understanding of how they apply. Good chance I'll learn something too.

A given source of power (engine output can be expressed in BTU's) produces combination of speed and torque that can be expressed as HP. Max engine HP and losses produces a set max output HP. A designer makes a choice between speed and torque to drive an output device but the HP remains the same--more rpm equals less torque for the same HP. However, an engine only produces output power sufficient to move a load at a demanded speed and how hard an engine works depends on the load.

If a MMM does work an engine harder than an rear mower of the same blade diameter then it may be because the blade speeds are higher. May be that MMM make a better cut because they have higher blade speeds and that's what requires more hp. Irrespective of the pto rpm it's the blades against the grass that produces the load. If the blade speeds are the same and the pto rpm's are different than the mowers have different gearing, and gearing in the mowers box has to be considered in the final torque applied to a load. Under-drives are sometimes called torque multipliers.






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 03-20-2004, 06:54 Post: 80463
hardwood

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 Mid PTO use?

TomG; Thanks again for your intrest in my project. I can't tell you the model number of the pump without going to the shop to look at the pump, but I do remember that it is designed to operate up to 3000 RPM and is also to operate in the correct direction. One of my goals is to elimenate any complex drives to the pump and have a direct hookup thru a universal joint PTO shaft. Any other ideas will be more than welcome, as I'm sorta in uncharted waters. Frank.






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 03-20-2004, 09:23 Post: 80467
beagle

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 Mid PTO use?

Tom good points, the Power curve of the engine tells you what Power is available at an operating rpm. A good unit to think of power in would be ft-lbs/sec. "Power" is the rate at which Work can be done, "Work" is Force applied x Distance. One Horsepower equals 550 ft-lbs/sec. A one hp engine can do the same Work as a 10 hp engine, but would theoretically take 10 times as long to get it done. An engine, due to mechanical and thermodynamic efficiencies, will reach maximum torque at a lower rpm than it will reach maximum hp.

After some digression, back to the original question. My feeling on the rear pto is based on the available torque at the shaft. Although the Power available at both shafts is roughly the same, the rear pto has about 4 times the available torque (about 1/4 the rpm). The mechanical advantage gained at the pto shaft would theoretically be lost if the mower is geared back up to the same blade speed. I'm not sure they are, which may explain why mid-mount mowers generally give a smoother cut, while rear mount mowers don't load the engine as heavily. I need to think about the angular momentum stored in the decks from the spinning blades, and what effect a heavy load at the blade has at the pto shaft. Because the rear is geared down, there may be an anvantage to the tractor there.

Thanks for the thoughts. Saturday morning, need another cup of joe to think this through.






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Discussion Boards > Active Subjects > Messages as Posted > John Deere Review Forum

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