Tow/Bypass Valve Limitations PT-425 & Perhaps Others

[SnowRidge]

Another bit of data you should find useful.

Temperature of the hydraulic fluid should not exceed 180ｺF (82ｺC) anywhere in the system. At higher temperatures, the fluid may start to deteriorate, and the viscosity gets too low for reliable lubrication of pump and motor components. As long as the fluid remains clean, stays below 180ｺF at all times, and contains no water (less than 150 ppm), there is no need to ever replace the fluid.

The Sauer Danfoss service manual disagrees with that. It calls for replacement of the fluid. The number of hours varies with the type of system. With the series 15 pump on my PT-425, it is 500 hours, and the fluid is to be changed.

 

[SnowRidge]

JJ,
Thanks for that link!!. it takes away the mystery of PowerTracs so called name for the pump. (Tram Pump). I've always called it a variable displacement piston pump.... same as the manufacturers, but PowerTrac likes to come up with their own little names. It's just like the Aux. Hydraulic circuit
( real name )... PowerTrac calls it an Aux PTO. circuit... last I knew...a aux. PTO circuit supplied power to an attachment via a drive shaft or a Hydraulic motor.. not a hydraulic cylinder in the case of the PowerTrac. It would be nice if PowerTrac stuck with Industry standards when naming their parts & components.

They call them tram pumps because they started out making mine trams. As far as I know, they still make them. The Power Trac is a derivative of the trams and uses a similar drive and control system.

The aux pto may drive a cylinder or a motor. It depends upon what you hook up to it.

 

[J_J]

The Sauer Danfoss service manual disagrees with that. It calls for replacement of the fluid. The number of hours varies with the type of system. With the series 15 pump on my PT-425, it is 500 hours, and the fluid is to be changed.

I don't disagree, I think the keywords are contamination, and filtration. If the fluid is clean, why change. The answer is not just because they said to change. I think a lab test would be a better indicator as to when to change. The expense is small compared to the expense of changing out a 100 gal tank.

 

[SnowRidge]

I don't disagree, I think the keywords are contamination, and filtration. If the fluid is clean, why change. The answer is not just because they said to change. I think a lab test would be a better indicator as to when to change. The expense is small compared to the expense of changing out a 100 gal tank.

PT-425 is 10 gallons. I imagine the 422 and 418 are the same or less. The older models don't have any kind of filter on the hydraulic tank vent. It's just a plain vented cap.

I plan on changing the oil this winter. I will have around 400 hours, perhaps a little more by then. I will also fit a filtered cap.

 

[J_J]

I am thinking that the hydraulic system on the PT's are closed loop systems. If they lose fluid, the charge pump makes up the loss. The charge pump is only pumping when it needs to. No, the case drains only pass fluid back to the tank. I am also thinking that the pump is designed to run in a certain direction, and when you tow it, you might be forcing fluid back through the pump in the wrong direction. Jamming things up, breaking things, etc.

I have a similar situation on my hydrostatic Wheel Horse, they say to not push or tow. Somebody did push it down some ramps to get it off, and it is now jammed up. There is supposed to be a release valve on there somewhere, but I have not found it.

I just wanted to correct myself about the charge pump. It appears that the charge pump is running all the time, but at a low psi. The fluid is used to charge up all the hydraulic circuits, and what is not used is sent to the case of the pump to help cool, and then out to the cooler or tank.

 

[MossRoad]

PT-425 is 10 gallons. I imagine the 422 and 418 are the same or less. The older models don't have any kind of filter on the hydraulic tank vent. It's just a plain vented cap.

I plan on changing the oil this winter. I will have around 400 hours, perhaps a little more by then. I will also fit a filtered cap.

How are you going to flush the pump and wheel motor circuits?

 

[SnowRidge]

How are you going to flush the pump and wheel motor circuits?

Dunno. I haven't thought that far ahead.

I figure that fitting the filtered cap is going to contaminate the tank, so that is a big part of what is driving me to change out the hydraulic oil. Worst case, whatever is in the pump and wheel motors will eventually get mixed with the new stuff in the tank.

 

[Rivco]

The aux pto may drive a cylinder or a motor. It depends upon what you hook up to it.

I don't mean to throw this thread off course, but in the case of the 422 & 425 you have a main PTO operating at 8 gal./min at 2500psi. supplying power to a hydraulic motor. How are you going to run a hydraulic motor off the third spool valve bank ( aux.PTO ) ?.

 

[SnowRidge]

I don't mean to throw this thread off course, but in the case of the 422 & 425 you have a main PTO operating at 8 gal./min at 2500psi. supplying power to a hydraulic motor. How are you going to run a hydraulic motor off the third spool valve bank ( aux.PTO ) ?.

Hold the lever down or up? Hydraulic winch comes to mind. The main PTO doesn't have to be in use.

My only point was the term "aux pto" is not nccessarily inappropriate.

 

[Bob999]

I figure that fitting the filtered cap is going to contaminate the tank, so that is a big part of what is driving me to change out the hydraulic oil.

Why?

I simply replaced the cap that came on my machine with a filtered one. I did have to buy a complete unit to get the filtered cap but I just didn't use the bottom part.

Got it at Surplus Center for less than $10. I posted a link to the specific part at the time.