travel pump

RegL · 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..

 Trouble is , even with 2 wheels in series, i have had one of those wheels spin while the other doesn't. I assume fluid leaks by the seals when enough load is applied to the wheel motor. So at a certain pressure and temperature would it not blow through the wheel motor no matter what the max pressure was set at? If anyone ever figures this out he's going to make PT hill people happy everywhere.

BobRip · Nov 7, 2005

There was a thread where we discussed this before. I believe that somebody makes a two speed wheel motor. They switch something (electrically) inside the motor to select the speed/torque range. How this works, I don't know.

I still suggest that if you are running 5w30 weight oil in your transmission that you change to 20W50 synthetic and also add some weight to the rear of the PT.

Bob Rip

stray · Nov 7, 2005

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.

Guys I will make this my winter time project. I feel sure that this will work and is what most of us that needs or wants more power will end up doing if we do anything. Give me a month or so to go over the schematics, talk with PT and an engineer or two where I work. I have worked on similar hydraulics systems and I don’t think that the cost for doing this will be near as much as swapping tram pumps or wheel motors. I get back to you all on this one.

KentT · Nov 7, 2005

Stray,

If you could come us with a reasonably cost-effective way to do that, you'd definitiely become a HERO to those of us who own older PTs....

So far, the lack of torque/hill-climbing ability when hot is my only complaint with these great little machines....

Kent

toolz_not_toyz · Nov 7, 2005

How about an even bigger project and possibly a better idea? Convert the PT 42x to electric! Just think, you could add a ton of weight with a bunch of lead acid batteries and also get gobs of torque from electric motors. The only downside is the limited run time. But you could design it so that the whole battery pack could get swapped out. That's what we used to do with our (much larger and much heavier) high reach warehouse forklifts. Heck, one of the battery packs in those things probably weighs more than a PT 425!

BT Reach Truck

BillCroasmun · Nov 8, 2005

Stray,
I'm definitly not an expert on hydraulics but I am trying to picture your concept with visions of water and/or air lines. If you have an air compressor or water pump putting out X lbs or pressure with Y amount of volume down a single line and you then divide the line into two parallel each new line would have half the volume but still the same pressure building up in each line. If I am thinking right, and if hydraulics work the same, putting each wheel on it's own circuit would decrease speed but would not increase torque.

I know I am not factoring in the "stuck and slipping motors" but I still think the total pressure in the line can not exceed what the compressor (or in this case pump) puts out. Hopefully I'm just missing something though...

KentT · Nov 8, 2005

FWIW, I've found this equation:

Torque = Displacement x Pressure / 24 PI

At this link:

Northern Hydraulics

If I understand what they're saying about a "series circuit" then Stray's idea may just work. In defining control valves, they state:

( SERIES TYPE: A multiple spool valve in which the return oil from the first spool is directed to the inlet of the second spool (and from the second to the third, etc.). This type valve permits simultaneous operation of two or more functions with the same oil flow. However, the total pressure requirements of all functions are accumulative. )
If I'm understanding that correctly, the first motor in the circuit "takes" half the pressure and the second motor "takes" the other half... So, if each were plumbed independently, each would get "full pressure" but 1/2 the current volume....

Also, searching the old posts, I found this link: Real Brakes for a PT Topic

In it, SnowRidge links the White wheel motor catalog, and gives the existing White part number of 400230W31222AAA

Using that, I appears that the existing "old wheel motors" are 14.2 cubic inch, 260 continuous RPM, 16 continuous GPM, and produce 4950 lb-in of torque continuous at 3000 PSI.

The next larger size, 15.9 cu in, is 18 GPM, and yields 6250 lb in of torque, a 26.3% increase over the current ones. The 2nd larger size, a 18.3 cu in, is 20 GPM, and yields 7100 lb in of torque, a 43.4% increase.

Does anyone know the specs on the variable displacement travel pump?

BillCroasmun · Nov 8, 2005

OK I think I get it now... The max pressure of the line is fixed by the pump but due to the way the motors operate in series they are effectively splitting that pressure in half. So putting them into a parallel configuration each will receive the full output pressure of the pump. The only question then is can the motors handle the full pressure of the pump? I'm sure if I re-read the thread now this was all probably stated already, just not clickin' in the ol' noggin' till now. /forums/images/graemlins/blush.gif /forums/images/graemlins/laugh.gif

MossRoad · Nov 8, 2005

Here's a link to an old thread but a good thread, on how an HST tranny works and more specifically, how a variable volume pump works.

There was, at one time, a working link to a military manaul on hydraulics, but, unfortunately, it no longer works.

However, I found a link to it here. /forums/images/graemlins/grin.gif

MossRoad · Nov 8, 2005

So putting them into a parallel configuration each will receive the full output pressure of the pump 

Yes, but the flow will follow least resistance, so the slipping wheel will get most of the fluid and the wheel with traction will get very little, so we will remain stuck. Isn't the PT setup considered a series/parallel setup?