Larger capacity hydraulic pump

[hayden]

Has anyone ever retrofitted their tractor with a larger hydraulic pump to increase oil flow? This could be a good way to get faster loader operation and more fluid flow for backhoes, wood splitters, etc. Increasing the flow too much would cause a problem with hoses and pipes that are too small, but I imagine it could be jacked up a bit without a problem. I have no idea who makes the pumps for different tractors and if they are readily interchangable.

Thoughts?

 

[MChalkley]

I don't know about other makes of tractors, but it can be done with most Kubotas. None of the tractor makers build their own pumps, so it's a matter of finding out the input shaft specs and mount dimensions and finding a replacement with the flow you want. For my previous L4310HST, for example, pumps with more than double the flow were available that would fit. Just because it would fit, though, doesn't mean you wouldn't create problems with the input shaft gearing. Increasing the flow meaningfully requires quite a bit more hp and if the power transfer components aren't able to handle it, you're going to have big problems. I'm comfortable enough with Kubota's overkill style of engineering that I wouldn't have second thoughts about an increase of 50% or so, but I sure wouldn't recommend it to anybody else. No matter how you slice it, making a change like that is going to reduce the life of something - my view is that it's probably going to last longer than I need it to anyway, so it doesn't hurt anything.

MarkC

 

[paccorti]

This reminds me of an idea I had the other day. A hydraulic pump has to operate under a wide variety of conditions. Sometimes when using the bucket to "break out" the pump should probably trade gallons per minute flow for increased PSI (so that the bucket or whatever can break out). Other times when the load is less the pump should trade PSI to move as many gallons per minute as possible (this obviously increases the speed of implements). Think of it as a load sensing pump. High load, gear down the pump and push less oil but at higher PSI; low load push as much oil as possible but sacrifice PSI.

In fact the situation is exactly analogous the driving a gear tractor in high or low gear. High gear goes fast but can't pull as hard, etc.

So why not use a hst pump in this situation? At a low swash plate angle the pump would move little oil but would have great ability to generate PSI, at a high swash plate you you could move lots of fluid. Of course there might be some problems with this. At the very least, it might be odd for implements to move at different speeds according to load. Perhaps there are other shortcomings...

Peter

 

[MChalkley]

Peter - It certainly could be done, but I expect things like expense are the determining factors in the choice for gear pumps for implements. Another reason may be that most implements and cylinders are rated not much higher than the relief valve setting, so increased pressures over what a gear pump can generate aren't practical, anyway. Besides, it's the flow, not the pressure that's of primary importance in powering most implements - this is certainly not the case with cylinders, of course, but, as I said, the gear pump produces all the pressure they can handle anyway.

You bring up a very interesting application, as it relates to HST transmissions, though. In the HST transmissions that most (actually, all, to my knowledge) CUT's use, a variable displacement pump is mated to a fixed displacement motor, with the displacement of the pump controlled solely by the operator of the tractor, via the HST pedal.

With the EarthForce machines, and most larger HST powered equipment, I've found out, they use a design called "automotive control", which incorporates a variable displacement pump and a variable displacement motor, with the displacement of the pump controlled by a combination of operator input, via an "accelerator" pedal, and backpressure from the motor. This "accelerator" also may or may not also control engine speed, depending on where the hand throttle is set, i.e. if the throttle is set at 2,400 rpm, the "accelerator" has no effect on engine rpm until it's depressed almost all the way down. Thus, you can set the engine rpm high enough to supply whatever hydraulics you need to the cylinders and/or implements, no matter what your ground speed is. The motor's displacement is controlled by internal pressure.

It all sounds pretty complicated, but the net result is a pretty versatile and easy to use system. For example, if you start out with the engine at idle and the tractor motionless, and floor the accelerator, the tractor will start out slowly, with both the pump at or near minimum displacement and the motor at or near maximum displacement and, as its speed builds, the pump gradually moves to maximum displacement while the motor moves to minimum displacement. At this point, highest ground speed, and lowest "power" (torque to the wheels) is being produced. If load increases, as in starting to climb a steep hill, the motor will increase its displacement, reducing its speed and increasing available torque, as its internal pressure builds, and the pump will also adjust to match the "accelerator" position and the load of the pump.

So, as you can see, one advantage of the addition of a variable motor to the system is the effect of an "automatic" range selector. It provides greater torque than a typical fixed motor, because it can have greater displacement in it's maximum displacement position than a properly sized fixed displacement one. On the other side, it provides much higher speeds (at lower torque, of course) at its minimum displacement position. It's a slick system, but a lot more expensive, too, of course.

MarkC

 

[MarkV]

Mark,

Does that mean with an “automotive control”, that uses a variable displacement motor, you would drive the EarthForce in a different way? With your old Kubota you would back off on the “accelerator” to gain power as needed for the grade in your example. This would lower your speed and give you the torque to manage the hill. If speed is your goal, you determined with the “accelerator”, engine rpm’s and experience, when you could increase speed again. Are we saying that with the “automotive control”, if speed were the goal, you leave it floored and the system adjusts for needed torque and returns to max speed as soon as it does not need the torque?

MarkV

 

[MChalkley]

MarkV - Yes, your description of the way you would use the EarthForce with "automotive" control is correct. (By the way, "automotive" is apparently translated from a German term as used in this application and is to be interpreted literally - it has nothing to do with automobiles.) You can't directly control the displacement (swashplate angle) of either the pump or the motor. However, the accelerator does bias the pump toward higher displacements - but if engine speed starts to suffer due to too much load (i.e. engine rpm starts to drop) the pump also senses the reduced input torque (from the engine) via reduced internal pressure and automatically reduces the displacement of the pump to compensate. I have a feeling it'll require a little getting used to, just like the "normal" CUT HST operation approach does. Still, in my test drives, it seems a very workable approach, and I really like what the variable displacement motor does for you - not having to stop to change ranges.

MarkC

 

[hayden]

Peter,

What you describe is a two stage hydraulic pump, and they can be found on most wood splitters. There are two pump wheels (or whatever shape they are) in the same housing, one big one that pushes lots of oil, and one small one that pushes less volume. Up to a certain pressure limit, the larger pump operates moving lots of oil at low pressure. As pressure builds, it loads down the motor that's driving the pump. When it gets to a set limit, ideally right at the limit of the engine's output, an internal valve switches to the smaller pump to effectively get a "downshift". The engine now driving the smaller pump has a greater mechanical advantage and can now build up to greater pressue since it's moving less oil to do so. The effect of this on the wood splitter cylinder is that it moves fast under light load, but when it hits the hard spots in the wood, it slows down (less oil flow), but develops much more force due to the greater hydraulic pressure. Without the "downshift" you would need a much larger engine to get the high GPM pump up to max pressue of 2500 PSI or so.

 

[paccorti]

Wow Mark, It sounds like you are getting a pretty cool machine there. One interesting point, the class III boomers (TC35,40,45) have a 2 position (displacement) motor. By flicking a switch on the loader joystick you select the motor position. Not quite a slick as your earthforce but still useful for high torque/speed situations within a mechanical gear range.

Peter Hayden - thanks for the description of the 2 stage pump. I didn't know that a simpler pump existed that achieves the same effect.

Peter

 

[MChalkley]

Peter - That's interesting - so are you saying that they have a dual displacement motor, two selectable displacements only? How is the variable displacement pump controlled? Do you own one of these tractors or have a shop manual for this tractor, by any chance?

One detail I neglected to mention about the EF-5 HST only: It has a high torque "snail" mode which, when engaged, forces the motor to maximum displacement, which sounds suspiciously like what you're talking about with the Boomers.

MarkC

 

[paccorti]

Mark,

Yes, I have the TC35D (an HST model). In fact YOU convinced me to get the HST! As I stated the motor is 2 position (9 and 15 degrees) and is operated by elect switch. The HST pump operates in the normal manner (by variable position swash plate). I do have the service manual (which is how I understood all of this). Remember the HST relief valve discussion ? If you are interested I'll scan a couple of pages for you.

If you don't mind my asking the Earthforce seems like a pretty serious machine, are you moving more from casual tractor user to profession? I ask only 'cause I do computer stuff too and a switch sometimes seems like a fun idea.

Peter

 

[MChalkley]

Peter - I would be very interested in seeing the pages that describe the HST design, if it's not too much trouble. Does it use a separate external pump and motor, or are they both contained within a transmission case as with the Kubota? If they're separate, do you know who makes them?

As for work, I do as much computer work as I have to to get by, but no more. It's just not something I like to do anymore. I'm not saying I think work has to be fun, but it's better that way, if you can get by. The reason for getting rid of the Kubota and replacing it with the EarthForce is pretty much evenly split between getting more power, more maneuverability, and more versatility. It's a tall order, but I think the EF-5 is going to fit the bill - with some enhancements, of course. /w3tcompact/icons/wink.gif

MarkC

 

[allmobile]

Kubota uses variable displasement hydraulic pumps on their KX series excavators. They work very well. you can use larger displacement pumps with lower HP since as the hydraulic pressure goes up GPM goes down.

Brian

 

[MChalkley]

Brian - That's interesting info. Do you know what kind of pump they use? I didn't think they used piston pumps on the implement side of things because of their sensitivity to contaminants.

MarkC

 

[paccorti]

Mark,

HST pump and motor are contained in the same housing (much like a Kubota I expect). Here is a scan from the manual. Notice the pump and motor in the bottom picture.

Peter

 

[paccorti]

Here is more detail on the motor. Notice that it has two positions.

Peter

 

[MChalkley]

Peter - Very interesting. Thanks for the scan! Sorry to be a pest, but if you get a chance sometime, see if there's a manufacturer plate or something on the housing that would indicate who the manufacturer is.

(BTW, you're right about the Kubota: it's built the same way the NH is. The EarthForce EF-5 uses a separate Rexroth pump and motor design.)

MarkC

 

[paccorti]

Here is the operation of the motor in the low speed (high displacement position).

Peter

 

[paccorti]

Mark,

I crawled around under there but did not see any obvious manufacturer identification...

So I'll bet you went through quite the selection press with regards to the new machine. I guess an L48 was not enough. This should open a new class of jobs for you (and close some others, no more PTO right?)

Peter

 

[MChalkley]

Peter - Thanks again - I didn't realize so much more info was coming! That tells me a lot. FWIW, the EF-5 Rexroth motor varies continuously from 0 to 25 degrees (with high torque mode forced to 25 degrees), while the pump varies continously from 0 to 35 degrees.

MarkC

 

[MChalkley]

Peter - Once again, thanks!!! I didn't mean tonight. /w3tcompact/icons/blush.gif

Yeah, it was an interesting 2 and a half months that I spent researching this decision. At least a dozen trips to all the equipment dealers I could find in Richmond and Hampton Roads, VA areas (and that's a bunch), plus 4 700 mile round trips to Tazewell, VA to look at the PowerTrac, and then a 7 hour round trip to Folcomer Equipment in Baltimore, MD, and culminating in a 1300 mile round trip to Summerville, SC to visit the EarthForce North American distribution facility, where I also met with the N.A. sales manager, the N.A. parts manager, the VP in charge of N.A. operations, and the President of the company himself (though seeing him was coincidental, not planned). I was very impressed with them and their equipment. I have to say, too, that I felt very strange being so impressed with the PowerTrac, then being that much more impressed by the EarthForce. I discussed the specific reasons in my initial post in the thread describing the EarthForce choice, but in the end it just underscored the engineering and construction superiority (for my purposes) of the EarthForce as compared to anything else I'd seen. I felt at first that I ought to be embarrassed to make such a change in my decision, but I finally decided that if I'd seen the EarthForce first, I wouldn't have even looked at the PowerTrac, so it wasn't indecisiveness on my part, but a lack of all the facts necessary to make the final choice. That's why I spent so much time making the decision in the first place.

As for the PTO, yes, I'll no longer have a mechanical PTO, but I'll have two hydraulic PTO, one on each end. Speaking of which, a friend of mine who owns an excavation company (and has a lot of big equipment) told me last week that he saw a hitch converter for skid steers that allows three point hitch implements to be mounted on a skid steer (sort of like the SpeeCo does), but has a hydralic motor with a PTO spline on it so you can attach a mechanical PTO shaft to it. That might solve my tiller problems, so he's trying to find it again - he doesn't remember where he saw it. If he does, I'll post it on TBN, of course.

MarkC