I was looking at getting a Gradall telehander. I have looked at them before in the mid 80's. I was thinking of one because pivot steer, visability, and I need a new toy, the main reason. They have I guess you call it hydrostatic drive with a pump on each wheels to drive it. What other machines use this type of system? What are the advantages to this or disadvantages? Seems more troubling than regular drive diff system on my Lulls. How long do the pumps last if maintained properly, and are they a headache? I guess it is one big pump driving the wheel pumps? When you let off the gas does the machine stop without brakes? Does this system use more fuel? If buying a used machine with 3-4,000 hrs what do you look for or do I need special tools for pressure testing to really know what is going on? Thanks for any help in advance.
I have a 1998 Gradall 534D6 that I bought new and put around 3K hours on it so far. The only things I have had to replace - starter, batteries, some small electrical switches and solenoids, which were available at NAPA and very easily replaced. As far as the hydrostatic drive - it has been bullet proof so far and IMOP far superior to any mechanical transmission/driveline. I had a 2004 Cat 460B with outriggers that was a workhorse but I still prefer the Gradall. (I sold the Cat a few years ago but still have 'ol blue ) The hydrostatic drive is far easier getting around the jobsite and placing loads. You let off the fuel pedal and the machine comes to a stop. The brake is used rarely. It has infinite "inching" capability due to the hystats. There is one main pump than runs the 2 rear hydraulic drive motors and one front drive motor for the fixed axle. The 4x4 switch is on the dash and is electronic. The diff switch next to the fuel pedal is rarely used unless you have very slippery conditions. Most of the time the machine is run in 2 wheel drive. My machine has a little cummins engine that still runs a as good as new. The fuel consumption is very affordable. We could run more than a week on a tank of fuel, I believe my tank capacity is 40 gals or so, not sure. I am not sure which other telehandlers run hystats but the Gradall is a good machine.
Hystats are good as long as the fluid has been taken care of and changed when it needed. Bulldozers use it, skid-steers, some skidders and some graders use it. Its strong and very tractive is slipery situations. It doesn't apply any jerking forces to the wheels so you can start out without spinning most of the time.
I believe all excavators, at least the current ones, use "hydrostatic drive", for the track drive, Speedpup. The swing mechanism on an excavator, would also be considered hydrostatic drive. Basically, any system that uses a "pump", to transfer a fluid to a "motor", and get "work" done, is a hydrostatic drive. http://en.wikipedia.org/wiki/Hydraulic_drive_system http://en.wikipedia.org/wiki/Hydraulic_motor http://www.hydraulicinnovations.com/index.htm OCR
thanks!
You're welcome, Speedpup. I do want to point out, Speedpup; my definition is a hair on the "crude" side... :cool2 So... chime in, anybody... OCR
Do you mean this part? I don't want to turn the hyd world upside down, but, the only thing I have a problem with the Wiki definition of "hydrostatic" is the phrase "any system". Not all hyd systems are "static", meaning, still, not in motion, at rest. A positive displacement pump system (gear pump) is not static. Nor can it be made static. It moves fluid (fluid is in motion) when it is turning. It can never be made "static" in it's operation. It, by design, is always producing fluid "in motion", always moving fluid, it is never "static" in it's operation.
I have a problem with the definition too... Here's what it states: To me, (my bold) this should be the definition of a "hydrodynamic" hydraulic system... that is, fulid in motion...fluid flow. OCR
Well, now after thinking about this for awhile, I have to argue with my own post... lol I don't think I have it right, but I don't know what's wrong with it... One thing we need, is a conclusive definition of the word "hydrostatic". OCR
It's like calling an International dozer a Cat, or any vacuum cleaner a Hoover. I've read somewhere that hydrostatic isn't correct for a pump / motor system as, already pointed out, the system isn't static. Hydrodynamic perhaps? The important thing is, talk about a hystat trans to anyone in the game and they know what you mean, like a Hoover, so to my mind that'll do. On the subject, my thinking is, not only are the newer systems easy to use and reliable, they're also much easier and cheaper to build than a powershift, from a manufacturer's point of view.
Well, I guess I should put the extent of my thoughts in here, as me and OCR have been discussing this in private messages. First of all, I don't claim to hold the definitive knowledge of the subject, I don't hold a degree in hyd engineering, and if I'm incorrect I'm certainly willing to be corrected. For the sake of clarity, in this post I am referring to terms and operations of hydraulic systems; pumps, motors, cylinders, actuators, etc. Now these terms may apply differently in other fluid power systems, such as transmissions, I don't know, and I'm not referring to these systems. Going back to the Wiki statement; "The term hydrostatic refers to the transfer of energy from flow and pressure, not from the kinetic energy of the flow." I've got to agree with you OCR...that's about the most ambiguous and convoluted definition I've seen for "hyrostatic". Back to the subject at hand, that being, the term "Hydrostatic". What does the word mean? Let's break down the word. "Hydro"; liquid, fluid. In this case, hydraulic oil and hydraulic systems. "Static"; still, at rest. A number of words can define "static", but they all imply the same thing; something "not in motion". So to remain true to the definition, "hydrostatic" can only be defined and applied as "fluid not in motion". In any hydraulic system, there are two and only two types of systems; 1) open systems in which oil is constantly flowing through the system. And, 2) closed systems in which oil is not flowing until it is demanded by some operation. You typically find open systems when using positive displacement pumps, such as a gear pump, since they produce oil flow while they are turning. Their displacement is positive, fixed, and constant. This can not be defined as a hydrostatic system, as fluid is in constant motion. Then you have closed systems with positive displacement pumps that use load sensing valves to dump oil back to tank when there is no demand by an operation, but the oil is still constantly flowing. This, as well, can not be defined as hydrostatic. To achieve true hydrostatic in a hydraulic system, the fluid has to be not in motion when no operations are being performed. The only way you can achieve motionless fluid is with a closed hyd system using a variable displacement pump, a pump that can litterally "reduce it's output" when there is no demand by an operation, or increase it's output when there is a demand, hence the term variable displacement. Therefore, with a closed system, and a variable displacement pump, no operations being performed, the fluid is simply "sitting still" in the pump awaiting a demand by a function, a true "hydro-static" system. And to take this a step further in common misuse of terms, it would be technically incorrect to refer to a hydraulic motor as being hydrostatic. After all, if oil were "static" in a motor...how could it be a motor as fluid would have to be moving though it in order for it to perform it's function? For that matter, we should not refer to a pump as hydrostatic as well. No I'm not crazy! The term "hydrostatic", contrary to Wiki, refers to a particular system or process of fluid control. It does not refer to the components of a system. The components (pumps, valves, motors) aren't in themselves hydrostatic, the components are how we achieve the process (system) of hydrostatic. Pumps and motors shouldn't be referred to as hydrostatic, but rather by their design operation of either fixed displacement or variable displacement. Wow, this post must take up some bandwidth!
Hydrostatic drive???? and excessive band width... lol Here's the book, and what the Authors have to say. It's a big book, so I took a picture of the page... that's why it's slightly rounded... lol Look at the third line... Piston Pump (Hydrostatic) But Wait!!! OCR
For less than the price of my bandwidth, I'll throw in a couple extra links. Wiki is right I think... but it's rather complicated. http://en.wikipedia.org/wiki/Fluid_statics This one is actually pretty good... technical though. http://www.hydraulicspneumatics.com/200/FPE/Hydraulics/Article/True/6450/Hydraulics Home page, I guess... http://www.hydraulicspneumatics.com/200/FPE/IndexPage.aspx And for fun. Does .9 = 1? ATCO couldn't get this figured out at all... ... lol http://en.wikipedia.org/wiki/.9 ... lol OCR...
But wait? You sly devil! Your a funny guy! Well bro, I don't see a disagreement with what I said. The author reaffirms my statement, sort of, that "hydrostatic means hyd pressure without motion". I kinda disagree in the sense that pressure is not necessarily a component of the term hydro (liquid) static (not in motion), but we'll go with it. Then the author goes on to describe how a typical "hydrostatic" system works. This is an important distinction; how...it...works. Not, "how it is "static" when it's not working. The author does a good job describing how the fluid enters the pump, how the pump processes the fluid, and delivers the fluid to the motor to perform the work before the fluid is returned to tank. Again, this does not necessarily disagree with what I said. Remember, the author described the system "working". When you describe what type of hyd system a machine has (hydrostatic/hydrodynamic), or if you look at any hydraulic or electrical diagrams (schematics), you always describe (or "show" in the case of schematics) the system "not working"...all things in neutral, no functions being operated. That is a standard of the industry. And in a true hydrostatic system, when nothing is being operated, the fluid is not in motion.
Yes I did! I told you in the case of the IRS...they would always go for the 1 instead of the .9999999-----
Hydrostatic drive???? and a lot of messing, on my part... lol Well bro, as usual, you were right... however, nobody was wrong either, at least in my opinion. More or less as stated by ih100... and me, in one or our numerous PMs, the "word" is basically the problem... I'm glad that's over... it is isn't it?????... OCR...
I hope so...you've dug farther into my brain than I have for a long time.
Hydrostatic drive???? ... ATCO's brain. Good stuff in there though, wish I would'a had an extenda-hoe... OCR
I'm thankful you didn't.