Mid PTO speed

[balsam]

I have a Kubota L3430 HST tractor and purchased a mid mount PTO for it. I was told the output RPM would be 1000 RPM. I just opened the box and, based on the size of the gears and shaft, I think it might be higher than that. They sure look pretty light to carry 30 hp at 1000 RPM.
Does anybody know what the RPM of the shaft will be if the engine speed is the 2550 RPM, which is the speed I run the engine at it get 540 at the rear PTO.
I should have asked this question before buying it, rather than taking a salesman痴 word for it.
Thanks

 

[zzvyb6]

Most mid-ptos are 2200 - 2500 rpm. You will need a reduction gearbox, belts or chains to get the rpm, torque level or direction you need to run some attachments from it. Now you can run a snowblower, broom or mid mounted mower from it. I have an air compressor that i dare run at idle rpm from it. You need a special driveshaft to hook onto it, too. A small generator could be a cool project to have 'hanging around' underneath. They can be run direct at 1800 rpm.

 

[diesel85]

Mid ptos are slightly different than front and rear ptos. Generally mid ptos are designed for equipment built by the manufacturer of the machine. Like mid mount mowers, brooms, snow blowers, etc. They often times have weird splined output shafts.

Rear and *most* front ptos are generally universal. Meaning the splines on the output are standard practice.

With that being said, you noted that it looked rather light.

First off, 540 rpm converts HP to torque. You'll get more torque off a 540 then you will with a 2500 rpm. 2500 rpm will give higher horsepower, but less torque. But you get the same amount of power. However, the 2500 rpm shaft doesn't need to be bigger.

To throw some maths out here... The relationship for a shaft driving something is simple: power = speed x torque (with the right unit conversions, of course.) So by increasing the speed, you can deliver the same power using less torque. 540/1000 = 0.54, or only 54% of the torque required to deliver the same power at 1000 RPM, vs 540 RPM.

Hence why if you look at the drive shaft of a 2500 rpm MMM, you'll see it's this tiny, puny little thing, compared to a 540 rpm rear mount drive shaft.

1000 rpm ptos are commonly found on larger 75+ HP tractors (and some smaller tractors as an option). Most of these are for mower conditions, hay balers, etc where they benefit from this "perfect" reduction. It also saves fuel and wear and tear.

Now in terms of your situation, I don't know if there is a 2500 rpm to 1000 rpm converter. I know there are 540 to 1000 rpm converters, but they incredibly expensive. You might as well use that as a down payment on a machine that has a 540/1000 rpm gearbox built in from the factory.

When I was working on the farm when I was a kid, we had two or three implements that ran on 1000 rpm. I remember having to pull the snap ring out and swapping output shafts. I also remember the time I got distracted and FORGOT to put the snap ring in.... the noise it made was horrendous. Luckily I didn't break anything.

 

[dstig1]

Manual says Mid PTO is 2000 rpm.

 

[johnems]

2000 rpm is what I run my front mounted snow blower an that in general is a sweat spot for North East snow.

 

[balsam]

Thanks guys, very helpful information.
Wow! Diesel, you know your stuff. I came to the conclusion that it was more than 1000rpm because I didn’t think the shaft and gear sizes couldn’t handle the torque...right for a change.
Thanks for straighten me out.

 

[dieselscout80]

Do all manufacturers mid PTOs spin the same direction?

 

[diesel85]

Nope. They can either be clockwise or counter clockwise. Also each gearbox can have it's own spline arrangement. So good luck finding an "aftermarket" driveshaft.

I'm kind of surprised that manufacturers haven't taken more advantage of high flow hydraulics. It would solve this issue with mid pto stuff, especially with the quick attach on these newer loaders.

I can't see where it would be advantageous for a manufacturer to make all these different sized attachments that run off a specialty mid pto, when they can make one model with hydraulic motors that can service many. I see so many questions asked on here about the Kubota front mount snow blowers, even variations in the SAME model number (A's and B's, etc) and what they are compatible with. Most of the time those letter variations in the model number refer to the mid pto shaft length.

Then I guess their argument is, the initial pump/transmission will be more expensive when buying the machine. But at least offer it as an option for those than want it/can afford it.

Would love to see a B or BX with high flow hydraulics and capability to run appropriately sized skid steer attachments. Then again, most SS attachments run in the neighborhood of 1000 lbs. So getting beyond that hurdle might be difficult to keep the price low for general consumers in the lower end models.

It would be neat to have a hydraulic motor operated mid mount mower... imagine no belt, no tensioners to worry about. Just have three motors, one for each blade. I think that is much simpler than worrying about designing a custom involute spline drive shaft, custom gearbox, belt, pulley arrangement, etc. That there alone in engineering would save money.

 

[jonsstihl]

the problem with that is that this gearbox and drive shaft technology is 50-80 years old and the engineering has long been paid for. these newer hydraulic setups require larger capacity hydraulic systems with more expensive components (open vs closed center) and are just not in the price point of the consumer market.

we have to be honest you and I would think it was cool and may be willing to pay extra for it but we are only 2% of the market.

 

[KWentling]

[QUOTE=jonsstihl; these newer hydraulic setups require larger capacity hydraulic systems with more expensive components (open vs closed center) and are just not in the price point of the consumer market.
we have to be honest you and I would think it was cool and may be willing to pay extra for it but we are only 2% of the market.

Hydraulics are also only about 80% efficient so less power available.

 

[MHarryE]

Most highly efficient piston pump for mobile equipment today is 92%. Pump and motor system is 92% x 92% = 85%. Gear pump and motor system 85% x 85% = 70%. These numbers don’t includes losses in valves, fittings, ant the losses go into heat. We figure 25% of hydraulic power needed to size hydraulic cooling system. Gears we figure 3% per gear set. Skid steers have a lot of hydraulic cooling capacity to compensate for the convenience of the hydraulic drive and of course how can you get a mechanical drive to the bucket end of a skid steer. Can’t beat the simplicity of a gear drive, one gear set to a mid mount PTO.

 

[Fallon]

Most highly efficient piston pump for mobile equipment today is 92%. Pump and motor system is 92% x 92% = 85%. Gear pump and motor system 85% x 85% = 70%. These numbers don’t includes losses in valves, fittings, ant the losses go into heat. We figure 25% of hydraulic power needed to size hydraulic cooling system. Gears we figure 3% per gear set. Skid steers have a lot of hydraulic cooling capacity to compensate for the convenience of the hydraulic drive and of course how can you get a mechanical drive to the bucket end of a skid steer. Can’t beat the simplicity of a gear drive, one gear set to a mid mount PTO.

Yup, more power, less fuel usage, more efficiency not to mention cheaper, generally with fewer parts. Hydraulics have much more routing options & generally a bit more control. But you cant beat a PTO shaft for impliments that use a significant portion of the machines HP

 

[dstig1]

So does anybody have any ideas of the torque or power that the Mid PTO is capable of? All the manual says is that it runs at 2000rpm whereas it gives PTO power for the rear 540 rpm PTO. Yes I know it varies by model, but I have no idea where to find that info for any model.

 

[Fallon]

So does anybody have any ideas of the torque or power that the Mid PTO is capable of? All the manual says is that it runs at 2000rpm whereas it gives PTO power for the rear 540 rpm PTO. Yes I know it varies by model, but I have no idea where to find that info for any model.

A mid-pto will output the same power as a rear PTO. Power = torque * RPM. If its spinning at 2,000rpm instead of 540, it has the same total power, just less torque. That goes for any machine.

(RPM * Torque in ft/lbs) / 5252 = HP. Not that the specific unit of power measurement changes the base principle.

 

[dstig1]

Thanks. Well yes, i get the math, but the question, I guess, is the input. Is it getting fed the same input as the rear PTO? If so, then I could agree that it has the same power, but I assumed given the tasks the Mid PTO is put to, that it is not up to the same specs. Do you know this to be the fact, or are you assuming? Not trying to be a jerk, just asking from where your response comes from.

 

[Fallon]

Thanks. Well yes, i get the math, but the question, I guess, is the input. Is it getting fed the same input as the rear PTO? If so, then I could agree that it has the same power, but I assumed given the tasks the Mid PTO is put to, that it is not up to the same specs. Do you know this to be the fact, or are you assuming? Not trying to be a jerk, just asking from where your response comes from.

Go back to the previous equations... If you double the RPM you half the torque. If you half the torque you can have lighter running gear to transmit the same power. In the case of a 2,000rpm mid PTO vs 540 rear, its transmitting just under a quarter of the torque.

It's the reason big tractors use a 1,000rpm PTO instead of 540. They can use lighter & cheaper running gear instead of what they would need to transmit the same torque at 540rpm.

 

[dstig1]

Well yes I get that, but as I asked, perhaps not clearly enough, was "is the input the same?" If it isn't, then the equations for the two PTOs are different. i don't know what happens inside the tractor to get to the PTOs...