Why Aren't PTO's Hydraulic?

[glennmac]

Why Aren\'t PTO\'s Hydraulic?

Why have we been shafted instead of oiled?

It seems that hydraulics power all the heavy lifting attachments: buckets, hoes, blades, cranes, derricks, etc. So, why aren't tractors designed to transfer power from rear and mid PTO's via hydraulics instead of rotating shafts.

Hydraulics must be more powerful, given their use on all the heavy lifting stuff. The attachment would also be easier to perform. A few light quick-coupling hoses instead of heavy, clumsy shafts. You have to be a real contortionist to get the shaft on a belly deck, a process that gets real old as you get real old.

Actually, Ingersoll makes a line of garden tractors that are completely hydraulically driven. I have always been impressed by them. They even give a lifetime warranty on the system. I don't know whether they put hydraulic PTO's on the larger Case tractors when Ingersoll was part of Case.

In a sense, this question is somewhat academic. Tractor manufacturers would now be deterred from offering hydraulic PTO's because they would be incompatible with the universe of shaft implements that now exist. But why didn't they offer hydraulics originally, or did they?

Glenn

 

[Harv]

Re: Why Aren\'t PTO\'s Hydraulic?

Glenn -

Just a wild guess here, but since you ultimately need to translate your hydraulics into rotary motion for most implements, you would be shifting that task to each implement. I assume that would make them more expensive.

Like I said, just a guess...

 

[Rowski]

Re: Why Aren\'t PTO\'s Hydraulic?

Glen,

I'll take a guess too... Cheaper (less complex) to design, maintain, repair/replace?

Derek

 

[Bird]

Re: Why Aren\'t PTO\'s Hydraulic?

I'm not real sure, but I think John Deere has a hay cutter that has a sickle bar operated hydraulically instead of via PTO. I suppose it would be a relatively simple matter to put a hydraulic motor on each implement instead of the current gearbox, but I'll bet it would cost a lot more, and then of course, your tractor would have to have adequate flow rate to operate it. In other words, I think it boils down to cost (and if someone knows better, I'll admit to not really knowing)./w3tcompact/icons/wink.gif

Bird

 

[Mike H]

Re: Why Aren\'t PTO\'s Hydraulic?

The comments on cost are accurate but a hydraulic PTO would probably be less powerful. All the energy in the tractor is coming from the combustion chamber. Every time the energy is converted, there are losses. Why add losses in the hydraulic system when you can connect right to the transmission? The losses are things like friction in the pump, line losses in the hydraulics, etc. Hydraulics are wonderful when your energy source (engine) and desired work (loader) are distant enough that connecting them mechanically is expensive.

 

[Anonymous Poster]

Re: Why Aren\'t PTO\'s Hydraulic?

FYI - Visit http://w3.one.net/~wduck/ for the history of the Colt/Case/Ingersoll garden tractors.

 

[Anonymous Poster]

Re: Why Aren\'t PTO\'s Hydraulic?

Don't know why the above link doesn't work. You'll have to copy & paste, sorry.

 

[scruffy]

Re: Why Aren\'t PTO\'s Hydraulic?

Dutchman, your above link worked just fine for me.

 

[TomG]

Re: Why Aren\'t PTO\'s Hydraulic?

The big augers on digging trucks that install electrical utility poles are hydraulic. I think I've heard of some smaller (maybe 3ph-post hole augurs) that are hydraulic. There are advantages to having something 'soft coupled' to the engine. However, augers on the digging trucks turn very slowly. I'm not sure how well a hydraulic engine would manage at 540 or 1000 rpm PTO speeds, and the engines certainly would be more expensive than gears.

Maybe the reason has to do with open centred hydraulic systems. Open centred systems flow oil through the system continuously. Oil is diverted to hydraulic cylinders on demand. My 8 gpm tractor pump is a not very big thing on the side of the engine. My 24 pto hp will run a pto pump somewhere in the 20's I think. So, to get full pto hp into the hydraulics, I'd need a very large pump on the engine that would just push a lot of oil around most of the time.

 

[art]

Re: Why Aren\'t PTO\'s Hydraulic?

There are losses that come with hydralic power as stated in the other posts. There is less horsepower to the wheels of a hydrostatic drive tractor than a gear drive. This would be the same as on a hydralic pto. Hydralics are expensive to build as well as repair costs and diagnostic time to fix. Post hole diggers are at there best when hydralic drives are used as when you catch a stone you can back it out instead of fighting to get the auger free. Larger tractors are using hydralics to engage the pto but it is still a positive drive with a shaft. If the numbers would be the same for a hydro trans as the pto for power loss you would be looking at a 7 to 10% power loss.

 

[glennmac]

Re: Why Aren\'t PTO\'s Hydraulic?

Art raises another potential benefit of hydraulic PTO's: you should be able to reverse the flow to make your implement spin the other way. This must have a use other than for augers.

If hydraulics are difficult to diagnose and fix, why has Case/Ingersoll always given a lifetime warranty on their all hydraulic tractors. In my experience manufacturers only give or sell extended warranties when they are convinced that they will not have much reason to honor them. That is also the reason why it is foolish to buy them.

Glenn

 

[art]

Re: Why Aren\'t PTO\'s Hydraulic?

Glenn the Case system isn't that fool proof. You have the chance of over speed which could destroy some equipment. In the area where I'm from they never sold many because on hills you had to use the brakes heavy to slow down. Those that did get sold here we often see after 20 years of lawn duty to staighten out drive problems that people have been unable to fix. To me I'm glad as a dealer I don't have that option to sell. There are people that could use this system but I know it would take more time for some simple explanations as to why the mower can't spin backwards and still cut grass. We hit probably 5 to 10 calls a year alone on blades put on upside down and the mower deck would just be one of the problems.

 

[W5FL]

Re: Why Aren\'t PTO\'s Hydraulic?

Glenn,

A Power Take Off is just exactly what it says. It allows any other device the same access to the engine directly geared as if it were part of the tractor. Many PTO devices depend on being driven at a fairly constant speed. There is absolutely nothing that a hydraulic system could do that the direct drive cannot do better. I would certainly hate to pay for the hydraulic motor (and the hydraulic pump) to run it to get the 62 HP that I get out of that 540 rpm PTO shaft now.

Hydraulic motors are nice, but very expensive. A good hydraulic auger that I would love to have is $2500. A $1000 gear driven unit is more powerful as most tractor hydraulic systems are not up to running them.

The auger that I need is $4500 and it will only use a straight PTO take off as it needs more power than you can conveniently obtain from a hydraulic motor.

Even a hydro transmission has enough slip in it that you cannot obtain constant ground speed that are required for some agricultural applications (spraying) etc.

Sorry, but I will keep the hydraulics for what they do best and use the mechanical pto for what it does best.

 

[gordon]

Re: Why Aren\'t PTO\'s Hydraulic?

Wen I have to ask what kind of auger are you looking at for $4500? Must be a monster! What can it do that my Danuser can't?
Gordon

 

[Anonymous Poster]

Re: Why Aren\'t PTO\'s Hydraulic?

So far, ALL above points but pro and con about hydraulics are lucid and valid. But,,,,,,,,,,,,,

Hydraulics are far more flexible. It is easier to buy and run a hose than it is to find and align mechanical components. Even a simple mower deck drive belt must be an exact replacement, where a broken hose can be replaced by one twice as long if necessary.

True, the initial expense of hydraulics is usually greater than mechanical. But, hydraulics are cheaper to maintain (a readily available hose or seal as opposed to a hard to find, obsolete, and expensive mechanical part).

Adequate power (engine, pump, cylinder, motor) is part of the design. Speed vs. Power? Consider a 2 stage pump. Closed vs. Open system? It depends on the application.

Surely, if you already have a PTO and a mechanical attachment, a shaft is the logical way to go. But, if your buying a log splitter, would you really consider a reversing gearbox/transmission, shaft, and worm screw? Do you think that might be more expensive and less efficient than hydraulic?

Just imagine an all mechanical road grader. I don't have to, I've got one, crank start and all. It's an all mechanical Caterpillar. It works! It's a marvel of mechanical engineering! It belongs in a museum along with the steam shovels, NOT on a job site!

 

[W5FL]

Re: Why Aren\'t PTO\'s Hydraulic?

Gordon, The Danuser is the best available for drilling in soil. This one locks the 3 point and has two hydraulic cylinders that put over 4000# of down force on the auger when it drills. Makes quick holes in chunk rock and drills holes in solid rock.

 

[gordon]

Re: Why Aren\'t PTO\'s Hydraulic?

I'd say that monster would make some quick holes with that much down force. I'd hate to price out the auger bit for that one ---ouch---. One thing goes without saying if you need it you need it. I'm not sure if threre is a downforce kit available for mine or not. Food for thought I guess.

On that Danuser I bought I would have sold it to you Wen but turns out I really like it and I'll never come across another deal like that on a F-8 in my lifetime.
Gordon

 

[W5FL]

Re: Why Aren\'t PTO\'s Hydraulic?

Yeah for about $450 a downforce kit is available, but it is not in the same ballpark for downforce. It helps when using a pry bar would help, but still will not drill rocks. The augers are about $1000. I see several of them in use in this area, so they must do the job for the fence companies and farmers with a lot of rocks.