Tow/Bypass Valve Limitations PT-425 & Perhaps Others

[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.