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.

 

[SnowRidge]

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.

If I remember correctly, I measured and did not have enough clearance to use that one. Either that, or it won't fit the neck on mine. I know others have had to cut off the original neck and weld the new one on.

However, I will take a look and see if they still have them. If they do I will recheck to see if one would fit.

 

[SnowRidge]

Bob, is this the one you used?

 

[ponytug]

Dear JJ,

Thanks for pointing this document out. The figures are great.

I guess that I am still a little confused. If the bypass valve is opened, it connects the forward/reverse side of the motors together. As you tow it, you have to force all of the oil through this valve. Clearly, that will generate heat(friction), which limits both the speed, and the distance that the tactor can be towed before the fluid is too hot.

But I fail to see how Eaton's comment about suction in the lines is an issue. If fluid leaks to the case drain, it can leak from the case drain as well. In the case of the PTs, this is flooded, and should, I think, be a non-issue.

Does it just come down to max heat load, and fluid temperature?

Now if I could just figure out which drive pump my 1445 used, I'd be in great shape.

All the best,

Peter

I think this document will explain things about the bypass valve. You can read the whole thing, but pay attention to pages 11/12

http://hydraulics.eaton.com/products/pdfs/03-205.pdf

 

[bjustice]

I think this document will explain things about the bypass valve. You can read the whole thing, but pay attention to pages 11/12

http://hydraulics.eaton.com/products/pdfs/03-205.pdf

JJ, thanks for that, just echoing Rivco (and many others over the years). The storehouse of information and knowlege that you have shared has been very valuable! Thanks!!
Bill

 

[J_J]

Dear JJ,

Thanks for pointing this document out. The figures are great.

I guess that I am still a little confused. If the bypass valve is opened, it connects the forward/reverse side of the motors together. As you tow it, you have to force all of the oil through this valve. Clearly, that will generate heat(friction), which limits both the speed, and the distance that the tactor can be towed before the fluid is too hot.

But I fail to see how Eaton's comment about suction in the lines is an issue. If fluid leaks to the case drain, it can leak from the case drain as well. In the case of the PTs, this is flooded, and should, I think, be a non-issue.

Does it just come down to max heat load, and fluid temperature?

Now if I could just figure out which drive pump my 1445 used, I'd be in great shape.

All the best,

Peter

I am thinking that the bypass valve is opening a small orifice for fluid from the wheel motors to circulate, and BYPASS the pump. In essence, tow slow. This will generate heat, and if the unit is towed or pushed for a long period, excessive heat will build up.

That fluid in the case drain, is forced there by the charge pump as excess fluid, and to help to cool the pump. If the charge pump is not running, no fluid is being sent to the case drain. Not only that, if the wheel motors are bypassing some fluid, there is no makeup fluid from the charge pump to refill the closed circuit. If you tow long enough, the pump may be empty of fluid, and when you start the motor, the pump will cavitate, and perhaps destroy itself. Just my humble opinion, and I am sticking to it, unless I am wrong.

 

[J_J]

Dear JJ,

Thanks for pointing this document out. The figures are great.

I guess that I am still a little confused. If the bypass valve is opened, it connects the forward/reverse side of the motors together. As you tow it, you have to force all of the oil through this valve. Clearly, that will generate heat(friction), which limits both the speed, and the distance that the tactor can be towed before the fluid is too hot.

But I fail to see how Eaton's comment about suction in the lines is an issue. If fluid leaks to the case drain, it can leak from the case drain as well. In the case of the PTs, this is flooded, and should, I think, be a non-issue.

Does it just come down to max heat load, and fluid temperature?

Now if I could just figure out which drive pump my 1445 used, I'd be in great shape.

All the best,

Peter

I have an older 1445, and I identified mine by looking at pictures of VSP pumps on the Internet. Perhaps if you posted some pictures with different views, use a mirror and good light, someone might come up with an answer. You might even ask PT for the manufacture of the pump and model number. If that doesn't work just threaten them with consumers affairs for withholding info for the repair and operation of the machine. You could also email that picture of your pump to all the pump manufactures, I'll bet someone can id the pump.

 

[SnowRidge]

I am thinking that the bypass valve is opening a small orifice for fluid from the wheel motors to circulate, and BYPASS the pump. In essence, tow slow. This will generate heat, and if the unit is towed or pushed for a long period, excessive heat will build up.

That fluid in the case drain, is forced there by the charge pump as excess fluid, and to help to cool the pump. If the charge pump is not running, no fluid is being sent to the case drain. Not only that, if the wheel motors are bypassing some fluid, there is no makeup fluid from the charge pump to refill the closed circuit. If you tow long enough, the pump may be empty of fluid, and when you start the motor, the pump will cavitate, and perhaps destroy itself. Just my humble opinion, and I am sticking to it, unless I am wrong.

Sauer Danfoss states that excessive speed in bypass mode causes the heat build up, and excessive time (length of push/pull) empties the case and lines due to internal leakage.

I don't think they state it explicitly, but it is pretty evident that the pump should be purged after any tow, no matter how short.

 

[Bob999]

Bob, is this the one you used?

Yes that is the one. I had to cut (shorten) the dip stick but otherwise was able to use the cap as is.

 

[J_J]

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.

A better word or words would be AUX HYD . You can use it for whatever, a cylinder, hydraulic motor, The aux hydraulic has a small pump, somewhere around of 1.5 to 3 gpm. At least mine does, and this same pump also controls the steering, lift circuits, and aux hyd.

 

[SnowRidge]

Yes that is the one. I had to cut (shorten) the dip stick but otherwise was able to use the cap as is.

Thanks, Bob. I will order one.