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PTO Horsepower and Generator Question
TomG, I've been following this thread without contributing but I'm very curious about the HST PTO HP issue.
Perhaps its an oversimplification on my part, but I figured that the HP loss was simply due to the pump always providing hydraulic flow and pressure, whether there was any real work being done or not. If the fluid has to flow and pressure needs to be built then the pump will sap HP even if the tractor isn't moving, regardless of pump design.
I'm probably missing something, but don't know what it is.
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PTO Horsepower and Generator Question
Art, I thought the issue was explained and settled. I'm sure no one meant to overtake the subject. I also always figured that the power loss was simply due to hydraulic pumps and the sheer physical size. Based on the principles of Dynamics that friction is always presant then generally a larger surface area with more parts were create a greater resistance. The one question I still have about all of this that you might help out with is on the larger pto driven gensets that seem to be intended to mount on a small trailer how do you get the pto shaft to run straight ? It seems if you use a telescopeing shaft and back to the trailer that your shaft would likely always be running at some angle. I also gather that the short answer and general consensus is that there would be no greater wear than normal use on a hydro in neutural to run a pto driven generator.
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PTO Horsepower and Generator Question
Art's comment is well taken. At least in this part of the thread I'm guiltily of mixing and matching principles and specifics and without a grasp of the specifics. All of these designs seem to be out there and Murf pointed indirectly to different properties of the designs, which is something I hadn't thought about.
So, from Murf's comment I did some digging and found the link above that summarizes the designs. The link also says the variable pump only type is likely to be found only on lawn and garden tractors due to torque limitation of the design. The design would save much of the HP that seems to be sopped up by a HST when a tractor isn't moving.
Since power is sopped up, I'd guess that most CUT's use a design where both pump and motor displacements are variable. A variable motor only design is inefficient at extreme ranges of operation and on it's own can't achieve zero speed or reverse. The pump likely has a load sensing design so pressure is maintained and oil bypassed as Bill and others mentioned. A geared range section reduces improves efficiency by reducing the ratio of displacements from the pump and motor required to achieve extreme ranges of motor speed
Anyway, that seems to be where the HP goes. I'm not sure why since I'd guess zero speed as well as reversing could be achieved by the pump swash plate. The answer likely has to do with coordinating operations of the pump and motor. But, that's enough of an answer for me although a bunch of blanks are left to fill in sometime. It's also probably the answer for Doc's question now a long way above. I'd guess most CUT pumps work against pressure all the time, and that's where the HP goes.
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PTO Horsepower and Generator Question
Guys relax, they have been installing new phones at the store and goofed up my connections so I've been trying to get a break during the day to do my internent work or play. On the hydro, it is hard to imagine but oil like water or energy takes the path of least resistance. The oil rather then taking a chance of being squeezed sneeks out and won't take the load. So you have a loss of power. That simple. A hydro is not a matter of a pump but you have a moveable swash plate that by changing the angle gives you your varied speed. Your pistons are made of brass and wear extensively with oil starvation. You are running pumps and that is where the loss of power comes from.
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PTO Horsepower and Generator Question
Doc, the shaft should be as near straight as possible. That is your work to make it as straight as can be.
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PTO Horsepower and Generator Question
Murf jumping in and going back to the swashplate activation. There are different types and the bulk of them in the older tractors do have the swashplate hooked in and that is where the work is done. I haven't seen many of the newer ones apart but from the days of old it was interconnected.
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PTO Horsepower and Generator Question
The link below goes to a site I ran across awhile back. The site likely supports a commercial idea of the owner but I haven't figured out exactly what is being sold or if it's interesting. The particular page linked to is about the sorts of leakage Art mentioned. There are a couple of other relevant pages on the site.
This mixing and matching of principles and specifics does get messy but I don't read any angst or even dismay here. When it works content should become more specific and less speculative. I think we've got to be messy sometimes to keep up our content quality and everybody eventually benefits. I know my grasp of both principle and specific have ratcheted up through this discussion and I hope others benefited as well.
Link:
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PTO Horsepower and Generator Question
My curiousity is sated. It seems it's just pumping losses and most any pump technology will have such losses when maintaining pressure and flow, even when stationary.
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PTO Horsepower and Generator Question
One more note on the hydro's for those in the conversation. The Case, Ingersall units do use a pump and motor to drive, that is why they freewheel downhill.
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PTO Horsepower and Generator Question
The links I thought I put in an above comment aren't there. I remember now that you can't put site addresses in text but I thought I included another one in link url box but maybe not.
Maybe interest in HST mechanics is exhausted for the moment but I included the links below the pump picture in the link below. The principles link describes constant torque, constant speed and other designs. The description is for a variables pump and motor design.
Link:
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Gas Generator Weather Protecti
08-18-2003, 22:03 
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