425 Bypass Valve Issue

[PT-425]

Hi Everyone,

If you haven't guessed, I have a PT-425. It's about 3 1/2 years old and I seem to be having some engine problems. I'd like to get it towed up to my garage which is a few hundred feet away. Having never needed to tow it before, I called Terry at Power Trac the other day to confirm the process for opening the bypass valve. I believe he told me to turn the valve 3/4 turn counter-clockwise (considering you're looking straight down at the valve and it being on the bottom side of the pump). I tried yesterday, but it just didn't seem to budge and I didn't want to force it too hard without further consultation from Terry. I did an obligatory Google search last night and found this forum. Maybe someone can give me some suggestions... am I turning it the correct way, is there a correct way to turn it, should it be turned 3/4 turn, should it be really hard to turn, etc.?

Also, it's really cold in central PA right now so I'm sure the oil is thick as molasses, but I wouldn't think that should keep the valve from turning.

Thanks in advance,
Aaron

 

[J_J]

Hi Everyone,

If you haven't guessed, I have a PT-425. It's about 3 1/2 years old and I seem to be having some engine problems. I'd like to get it towed up to my garage which is a few hundred feet away. Having never needed to tow it before, I called Terry at Power Trac the other day to confirm the process for opening the bypass valve. I believe he told me to turn the valve 3/4 turn counter-clockwise (considering you're looking straight down at the valve and it being on the bottom side of the pump). I tried yesterday, but it just didn't seem to budge and I didn't want to force it too hard without further consultation from Terry. I did an obligatory Google search last night and found this forum. Maybe someone can give me some suggestions... am I turning it the correct way, is there a correct way to turn it, should it be turned 3/4 turn, should it be really hard to turn, etc.?

Also, it's really cold in central PA right now so I'm sure the oil is thick as molasses, but I wouldn't think that should keep the valve from turning.

Thanks in advance,
Aaron

Aaron,

I don't know if this will help or not, but draw the lever or bar that you are supposed to turn, on a small piece of paper. draw an arrow to the left which is the counter clock direction. Now turn the drawing upside down, since you said the lever or bar was on the bottom of the pump, look and see if you are turning it in the correct direction.

On my 1445, the bypass lever or bar is on the top of the pump.

 

[PT-425]

Thanks J_J,

That could very well be the problem... turning the valve the wrong way. Unfortunately explaining which way to turn a valve that's on the underside of anything can be difficult to explain over the phone. I thought Terry said to look down at it and turn counter clockwise. I'll probably just call him tomorrow and ask if I should turn the valve clockwise or counter clockwise regardless of which side of the pump the valve is on.

Is it common for a valve to be turned 3/4 turn? For whatever reason I envisioned this valve like a ball valve... turn 90 degrees and it's open... turn back 90 degrees and it's closed. I guess turning it 270 degrees would do the same thing in this instance. I apparently don't have a clue about how this valve operates.

Thanks again for the info.

Aaron

 

[J_J]

Thanks J_J,

That could very well be the problem... turning the valve the wrong way. Unfortunately explaining which way to turn a valve that's on the underside of anything can be difficult to explain over the phone. I thought Terry said to look down at it and turn counter clockwise. I'll probably just call him tomorrow and ask if I should turn the valve clockwise or counter clockwise regardless of which side of the pump the valve is on.

Is it common for a valve to be turned 3/4 turn? For whatever reason I envisioned this valve like a ball valve... turn 90 degrees and it's open... turn back 90 degrees and it's closed. I guess turning it 270 degrees would do the same thing in this instance. I apparently don't have a clue about how this valve operates.

Thanks again for the info.

Aaron

I can answer that. What the bypass valve is doing, is to operate both relief valves in the tram pump, allowing the fluid coming through the input side of the relief valve to flow through the output relief valve back to the input, otherwise just making a loop. You can not do this very long, because the orifice for the relief valves are rather small. The fluid will heat up if done for a good length of time. I think the manual says to tow the machine slow and not a great distance.

 

[MossRoad]

Welcome to TBN!

 

[Marks481]

be careful; with the "tow" valve open, you should only move it at less then a walking pace... and then only for a few hundred feet.

to call it a "tow" valve is definitely misleading.

http://www.tractorbynet.com/forums/...valve-limitations-pt.html?highlight=tow+valve

 

[ponytug]

Yup. You are right. It just bypasses the relief so that the wheels can turn, but
a) the fluid reciculates, heating up, and
b) any leakage(e.g. back to the tank) might undermine the lubrication of the wheel motors. (At least that's what Eaton worries about.)

I found it to be an informative thread. From what was discussed, and the PT design, I don't fully understand why towing at ultra low speeds is seriously evil in the case of PTs, but I defer to the hydraulic wizards out there.

On the other hand, do you really want to be servicing it where it pooped out?
Or try to drag it with 4 locked wheels? (Not that that would be great for the wheel motors either...)

Good luck!

All the best,

Peter

be careful; with the "tow" valve open, you should only move it at less then a walking pace... and then only for a few hundred feet.

to call it a "tow" valve is definitely misleading.

http://www.tractorbynet.com/forums/...valve-limitations-pt.html?highlight=tow+valve

 

[J_J]

Yup. You are right. It just bypasses the relief so that the wheels can turn, but
a) the fluid reciculates, heating up, and
b) any leakage(e.g. back to the tank) might undermine the lubrication of the wheel motors. (At least that's what Eaton worries about.)

I found it to be an informative thread. From what was discussed, and the PT design, I don't fully understand why towing at ultra low speeds is seriously evil in the case of PTs, but I defer to the hydraulic wizards out there.

On the other hand, do you really want to be servicing it where it pooped out?
Or try to drag it with 4 locked wheels? (Not that that would be great for the wheel motors either...)

Good luck!

All the best,

Peter

Peter,

To be technically correct, both relief valves are open by turning the bypass lever. Since this system is a closed loop system, the fluid in the bypass mode recirculates through the wheel motors and part of the tram pump, the relief valves. The main purpose of the tow/bypass valve , is to have somewhere for the fluid to go. The output of the tram pump is relieved back to the input. Once again, heat is the limiting factor. If the fluid does not heat up, you could tow for miles.

One trick you might consider, is if your PT is dead way back in the woods, You could take your wheels off, and skid it home on the belly pan with another tractor, or 4 wheel drive truck. You could also make a log type skid.

In addition, since there is no or very little pressure in the system, there is no oil to lose or drain back to tank.

 

[ponytug]

Dear Terry,

Exactly-I completely agree, and personally that is where I had ended up in my own mind. However, that's not quite where the thread ended up and it isn't what the Eaton document says. The PT oil system is flooded and it seemed to me that if one were to keep the towing very slow, then the primary concern would be that the oil not overheat.

Well maybe not your primary concern, since we are talking about towing a dead PT...

All the best,

Peter

Peter,

To be technically correct, both relief valves are open by turning the bypass lever. Since this system is a closed loop system, the fluid in the bypass mode recirculates through the wheel motors and part of the tram pump, the relief valves. The main purpose of the tow/bypass valve , is to have somewhere for the fluid to go. The output of the tram pump is relieved back to the input. Once again, heat is the limiting factor. If the fluid does not heat up, you could tow for miles.

One trick you might consider, is if your PT is dead way back in the woods, You could take your wheels off, and skid it home on the belly pan with another tractor, or 4 wheel drive truck. You could also make a log type skid.

In addition, since there is no or very little pressure in the system, there is no oil to lose or drain back to tank.