travel pump

KentT · Nov 6, 2005

MR,

It just seems that it would be simpler to replace the pump than to replace all four wheel motors, if it would produce the same/similar results...

I know in a pulley drive system, you can change either pulley, or both...

MossRoad · Nov 7, 2005

I don't know if it works the same with the hydraulics. The principle sounds right, however, I'm trying to get it straight in my mind...

For example #1 I'll use the same pump and change motors:

First set of motors gets you a top speed of 10MPH at 3000 PSI and 8GPM.

Second set of motors gets you a top speed of 5PMH at 3000 PSI and 8GPM.

First set is whimpy in torque, but good top speed.
Second set is very good in torque, but no top speed.

I can understand how that example works because you just change the gearing internally of the wheel motors to get what you want. Select the wheel motors with the internal gearing to give you the torque or top speed that you want, but you can't have both. Very simple example for me to understand... /forums/images/graemlins/smile.gif

Second example I'll keep the motors the same and change the pump:

First pump gives you 10MPH.

Second pump gives you 5MPH.

How? I can't figure that part out because.... we are limited by the maximum PSI that the motors, hoses, fittings and seals can handle. If the second pump gives good torque and low MPH, the only way to get the 10MPH out of the motors is to UP the GPM of the pump to get 10MPH. If you UP the GPM, the motors have to be able to handle that GPM, AND, the engine will have to be able to push that pump, etc...

I think the best bet would be to size a pump to an engine for the maximum GPM at 3000PSI and then size the motors for the job you intend to do... low RPM for high torque/low speed and high RPM for lower torque but higher speed.

Then, however, we vary the volume, or GPM of the pump with the treadle pedal....YIKES! Now I'm confused even more! /forums/images/graemlins/grin.gif

The PT is a compromise between high torque and good top speed because there is no high/medium/low range like a farm tractor. There can't be because the way a farm tractor HST works is different. A variable volume pump drives a shaft that turns a gear box. If you want lower gears, you shift the gearbox. You cut out top speed for low torque, yet maintain the variable volume pump. So PT compromises by choosing the low to medium end of the spectrum by eliminating a gearbox and sizing the pump and motors to get a decent amount of torque for the jobs the machine is sized to do, yet give it enough top speed to get around the worksite at a reasonable clip.

Geez, sorry for the long windedness of the post... but you see what I'm getting at. If you can explain it to me a bit better, I'm willing to learn.

tracdoc · Nov 7, 2005

Whew! /forums/images/graemlins/confused.gif I think I follow your post MR....I know, it's Monday morning, and maybe I should have another cup or two of Joe and then re-read it /forums/images/graemlins/grin.gif

stray · Nov 7, 2005

I just had a thought and would like to here some discussion around this. You know that the PT wheel motors are 2 in a serious. The front right and the back left, the front left and the back right. What if one would put them all in parallel line or each in its own circuit. Wouldn’t this make the PT something like twice as slow and geared with more power. What if one could rig it so you could swap back and forth. JUST SOME FOOD FOR THOUGHT. HOW ABOUT IT.

No compromise the best of both worlds. Isn't that what we really want? Let's maybe call PT and ask them. Bet they won't want this to be well known. What do you say guys???? Am i thinking in the right or wrong direction???

MossRoad · Nov 7, 2005

I think with the wheel motor circuits in parallel, the one that has the least resistance will get the most fluid. If that is the case, the slipping wheel would get more juice to slip some more while the other wheels get no juice. Does that sound right? /forums/images/graemlins/confused.gif

toolz_not_toyz · Nov 7, 2005

That sounds right to me MR. And that's probably why PT designed the system with a crossover layout. The idea being that two wheels that are diagonally opposed will always be on the ground vs the other two wheels. I guess you could test that theory by extending the rear two wheels over a cliff and checking to see if the front two will pull you to safety. /forums/images/graemlins/crazy.gif

On the one hand it sounds like a great idea to have a system that could be switched from low torque to high torque that way with the tradeoff being loss of (or dramatically lowered) traction. But on the other hand the question that has to be considered is: when you need low torque don't you typically also want high traction?

KentT · Nov 7, 2005

I'd sacrifice top-end speed permanently in order to get more torque -- on mine, it is so quick that it can be downright dangerous. I'd love to have twice the torque and half the top-end speed for my uses...

It would certainly be nice to know what the original design parameters were for the pump and wheel motors...

I'm thinking the only way to increase torque with the existing wheel motors is to increase pressure in the circuit, while speed is a factor of volume....

MossRoad · Nov 7, 2005

I'm thinking the only way to increase torque with the existing wheel motors is to increase pressure in the circuit, while speed is a factor of volume.... 

O.K. That sentence makes sense to me.

If you increase the pressure, won't you damage the motors and pump? How much is too much? /forums/images/graemlins/crazy.gif

KentT · Nov 7, 2005

(
If you increase the pressure, won't you damage the motors and pump? How much is too much? /forums/images/graemlins/crazy.gif )
How much is enough? /forums/images/graemlins/cool.gif

Without knowing the original specs, it's hard to even speculate... /forums/images/graemlins/confused.gif

Gravy · Nov 7, 2005

I'm with you - I rarely go over half speed, but I'd sure like more torque. There are a bunch of good firewood trees at the top of this one slope that I can only get up before the fluid gets hot. My 425 will be out of warranty after Thanksgiving, and I'll be looking for ways to boost the torque...

Gravy