More torque for my Power trac?

[KentT]

IMO, you're simply running into the limitations of the White RS wheel motors.

1. To quote White: RS Series motors are the most economical model in the White Drive Products product line.I know that when the original oil in my PT was hot, I could get it in situations where it simply would not move the PT, nor would it stall the engine. It would leak/bypass all the output of the tram pump. The PT would simply sit there and whine... Changing to AMSOIL syntheict 20W50 stopped that, and I could bog the engine down, but it still wouldn't climb out of some of the situations...

2. Most importantly, perhaps, are the basic specs of those 12.5ci motors. Under ideal conditions, no wear, the motors are only capable of producing 3050 in lbs (254 ft lbs) of torque at 1750 PSI, the max intermittent pressure the motor will handle, or 2640 in lbs (220 ft lbs) of torque at 1500 PSI, the max continuous PSI the motors will handle. That's the limits of the motors....

3. Then consider the tram pump itself -- I'm not certain of the specs for it, but I think it is a 2500 PSI, 16GPM pump -- which would actually exceed the power demand that the 25HP Kohler can produce, when combined with the PTO and steering/lift/tilt pump. I doubt you're ever spiking over 1500 PSI in a drive circuit, and likely running something like 1250 PSI normally. Bottom line is that you likely have wheel motors producing less than 200 ft lbs of torque -- with no other demands on the system (steering , PTO, etc.).

I can easily generate far more than 200 ft lbs of torque on my 1/2" breaker bar... no wonder this thing won't climb steep hills...

In comparison the 22.7 ci CharLynn S series motors that I put on mine can produce 390 ft lbs of torque at 1250 PSI (max continuous operating pressure) or 433 ft lbs of torque at 1500 PSI (max rated intermittent pressure). I ordered the optional high-pressure seals just to make sure the seals would handle those kinds of spikes, if necessary.

IMO, there's no substitute for displacement when it comes to torque....

 

[SnowRidge]

Thanks for being the straight man!

This is my point: the hydraulic fluid will always flow to the the wheel with the least resistance, if it is plumbed in common. And, apparently, all of our tractors are plumbed in common. Powertrac would have had to install some rather expensive flow matching devices to create separate circuits.

SO, the tractors will climb the best when all four wheels are on the ground, and in good contact with the earth. Slippage of any one wheel will unload all of the wheels.

All the best,

Peter

Bolding added.

No it won't, at least not on the PT-425. It's the only model I have direct access to, so I am not in a position to state the same for any of the other models. But I will categorically state that slipping of any single wheel on a PT-425 will not unload the rest of them.

The front and rear wheels on each side are plumbed in series. The two sides are plumbed in parallel. If any single wheel slips, its series connected mate limits the amount of flow to the slipping wheel so that it can not rotate any faster than the its mate. The non slipping wheel on that side absorbs all of the hydraulic power delivered to that side.

The only way to partially unload all the wheels is to have two on the same side off of the ground at the same time. In that case, some fluid will still be delivered to the side with traction due to the restrictive size of the T fittings and whatever power absorbing qualities remain in the motors on the off the ground side. It is impossible to completely unload all the wheels.

The only way to get in this situation is to longitudinally high-center the machine with both wheels on one side in a ditch and both wheels on the other side off of the ground. Despite owning a whole bunch of rough Tennessee hillside, called vertical acreage by a friend of mine, I have yet to stick my PT-425 anywhere.

 

[SnowRidge]

3. Then consider the tram pump itself -- I'm not certain of the specs for it, but I think it is a 2500 PSI, 16GPM pump -- which would actually exceed the power demand that the 25HP Kohler can produce, when combined with the PTO and steering/lift/tilt pump. I doubt you're ever spiking over 1500 PSI in a drive circuit, and likely running something like 1250 PSI normally. Bottom line is that you likely have wheel motors producing less than 200 ft lbs of torque

Here are the pump specs. Before anyone asks, I don't know why the implement relief is so low.

Ignore the motor specs. Companion motors are covered in the same document. They aren't used on our machines.

Note: Our pumps appear to be configured slightly differently than the standard models. They may have Power Trac specific specs.

 

[KentT]

Here are the pump specs. Before anyone asks, I don't know why the implement relief is so low.

Ignore the motor specs. Companion motors are covered in the same document. They aren't used on our machines.

Note: Our pumps appear to be configured slightly differently than the standard models. They may have Power Trac specific specs.

Where did you get those specs? What document are they from? Is it the Italian manufacturer's data?


I agree that those pressure relief numbers are VERY low. At 750 PSI, the White 12.5 ci RS motors produce a max of 1386 in lbs (115 ft lbs) of torque, at a 2 GPM flow. I would've guessed about 1250, as I said...

It would certainly be interesting to put a pressure guage on the tram output lines, then put the PT up against a tree and see where bypassing (i.e. relief) begins...

That may be Stray's easiest torque enhancement -- to tweak the relief valve setting, now that the machine is long out of warranty...

 

[SnowRidge]

Where did you get those specs? What document are they from? Is it the Italian manufacturer's data?

They are from the Sauer Danfoss service manual. The PT-425s don't have the Italian Bondioli & Pavesi tram pump. At least mine doesn't.

Here is a link to the PDF version of the service manual.

And here is a link to a technical data sheet.

 

[SnowRidge]

Further reading indicates that the implement ports are auxiliary ports not used on the PT-425. Apparently, the implement relief is not in the wheel motor circuit after all. That would explain the seemingly low opening value.

One thing that is in the wheel motor circuit is the bypass valve. A bad or cracked open bypass valve might also explain Stray's problem.

 

[MossRoad]

On my PT425 I thought the right front and left rear were in series and the left front and right rear are in series, then those two circuits are in parallel.

The reason I do not think the wheel motors are in series on the same side is because when you turn the tractor, the wheels on the same side either roll away from each other or towards each other. If they were in series they would have to roll in the same direction.

Does that make sense?

 

[SnowRidge]

On my PT425 I thought the right front and left rear were in series and the left front and right rear are in series, then those two circuits are in parallel.

The reason I do not think the wheel motors are in series on the same side is because when you turn the tractor, the wheels on the same side either roll away from each other or towards each other. If they were in series they would have to roll in the same direction.

Does that make sense?

Nope, because when the machine turns, the wheels on the outside of the turn have to rotate faster than the wheels on the inside of the turn. If the opposite corners were series connected, it would be like having lockers front and rear, which would tear up the ground.

The left to right differential action comes from having the sides in parallel. The series connected motors on each side provide "positive traction front to rear." So sayeth the PT service training material that I got when I picked up my machine and attended Terry's training section.

It you turn the machine when it isn't rolling, you get a combination of scuffing, hose damping, and a wee bit of oil bypassing in the motors.

 

[KentT]

Further reading indicates that the implement ports are auxiliary ports not used on the PT-425. Apparently, the implement relief is not in the wheel motor circuit after all. That would explain the seemingly low opening value.

One thing that is in the wheel motor circuit is the bypass valve. A bad or cracked open bypass valve might also explain Stray's problem.

I'm glad to hear that the Model 15EV is tram pump -- it's a very commonly used pump and means that I could get it worked on somewhere other than Tazewell, if necessary. Unless I'm mistaken it was used on the larger Simplicity garden tractors with Sundstrand transmissions. They used that optional implement port to power the hydraulic implement lift -- and that circuit operated at 750 PSI...

By the way, the specs on it essentially confirmed my own "sizing assumptions" -- 2500 PSI continuous operating pressure (1250 PSI per wheelmotor) and about 14 GPM, instead of the 16 GPM I had guesstimated... and, coming full circle, that means the 12.5ci wheel motors in ideal conditions would output about 185 ft lbs of torque at 1250 PSI. To put that in perspective, that is essentially the same torque that a 185 lb person hanging onto the edge of the 23" tire would generate -- that's not a lot of torque folks...

BTW, the link you provided to the service manual doesn't work...

 

[J_J]

Further reading indicates that the implement ports are auxiliary ports not used on the PT-425. Apparently, the implement relief is not in the wheel motor circuit after all. That would explain the seemingly low opening value.

One thing that is in the wheel motor circuit is the bypass valve. A bad or cracked open bypass valve might also explain Stray's problem.

SnowRidge,

On my 1445, I have the Eaton VSP pump, and I believe the bypass valve is nothing but a screw in or out adjustment to open both relief valves in the pump, so the fluid from the motors can recirculate back to the input. so that the PT can be towed with say a dead engine.

Also, when turning, one wheel motor slows down, and the other one speeds up, acting like a spider gear. Parallel in the front, and parallel in the rear.