level creeping

[coglesby]

Since the Hydac valves on the manifold for leveling are on the extend side, if one is leaking, I assume that the leveling jacks would retract on the side that is leaking?

One side is retracting while the other side is extending, but I think the extending is due to the weight shift. Just trying to figure out which valve could be leaking.

 

[triplethreat]

I stand corrected

It's kind of complex little system they have there for the hydraulics, and I wanted to make sure that I didn't mess it up when I changed out the lines, both from the manifold to the curbside leg, but also the set of lines from the curbside legs over to the streetside legs. If I remember correctly, I took some black tape and wrapped it around the line that would be the Black line and covered up any Red that was on the replacement hoses that I bought....just to be safe. I can remember smiling a bit when I got done and pushed the extend button and then the retract button for the front legs....and they worked exactly like they were supposed to.......Whew! and a sigh of relief.

 

[Hoopy Frood]

Since the Hydac valves on the manifold for leveling are on the extend side, if one is leaking, I assume that the leveling jacks would retract on the side that is leaking?

One side is retracting while the other side is extending, but I think the extending is due to the weight shift. Just trying to figure out which valve could be leaking.

Just a thought: If one side middle and rear leak down, then the trailer WILL tilt. The front two legs are tied together so if one has more weight on it, it will lower while the other rises. So the extend valve could be leaking for the rear and middle legs on one side.

 

[triplethreat]

Since the Hydac valves on the manifold for leveling are on the extend side, if one is leaking, I assume that the leveling jacks would retract on the side that is leaking?

One side is retracting while the other side is extending, but I think the extending is due to the weight shift. Just trying to figure out which valve could be leaking.

In thinking about it, it may just be as you said.....a slight leak back through the valve and a weigh shift going on....but I'll be honest with you, I'm certainly not a hydraulic expert, but I have worked on some hydraulic stuff over my career.

One way to tell which one is which for the mid and rear legs and which valve controls the curbside and which valve controls the streetside is this. Mark all four of the wires that attach to those two Hydac valves and draw a picture of them on the bottom of the manifold. Then mark up the picture with the wire numbers that you previously marked. Doesn't need to be anything fancy, just #1 on say the first valve and the terminal closest to the manifold. Then #2 on the other wire that is on that same valve. Then #3 on the next Hydac valve and the terminal closest to the manifold, then #4 on the last wire.

After you get them marked, and the picture drawn of where they go back, pull one set of wire off of ONE of the valves....totally take both wires off. Then manually try to operate the curbside mid/rear legs....using the One control app on your phone or the tablet in the trailer in manual mode. If your curbside legs operate with the wires off of one of the valves, now you know which one is which and you can mark the Hydac valves as such.....curbside for one and streetside for the other.

 

[coglesby]

I'm going to label the manifold using the method you described. I can see the one that goes to the slides because there is a separate manifold for the slides. I can see which one goes to the LG easily too. The leveling jacks hoses just disappear into the cavity where the tanks are so not easy to trace. I'm going to try the "Lucas conditioning and stop leak" first and exercise the system to see if I get lucky and that works.

 

[triplethreat]

Just a thought: If one side middle and rear leak down, then the trailer WILL tilt. The front two legs are tied together so if one has more weight on it, it will lower while the other rises. So the extend valve could be leaking for the rear and middle legs on one side.

Howard, I don't believe the front legs will change at all, even if the rear and mid legs on one side leak down. The front legs have their own Hydac valve and it's located on the curbside front leg. In fact, because the front legs won't move, that may actually introduce a bit of frame twist because the mid and rear are not as high as the front leg.

 

[Hoopy Frood]

Howard, I don't believe the front legs will change at all, even if the rear and mid legs on one side leak down. The front legs have their own Hydac valve and it's located on the curbside front leg. In fact, because the front legs won't move, that may actually introduce a bit of frame twist because the mid and rear are not as high as the front leg.

I don't know, since the legs are interconnected, it might be possible for excess pressure, from increased weight on one could bleed into the other leg. But I really am just guessing, pretty much anyway. I do know that if I raise the rear/middle legs to get the tires off the ground, and introduce a bit of tilt, the legs in front will also tilt. So I think they can interact with each other, but both together cannot increase or decrease in height. It would have to be one increase, and one decrease. That's probably about as clear as mud.

 

[triplethreat]

I don't know, since the legs are interconnected, it might be possible for excess pressure, from increased weight on one could bleed into the other leg. But I really am just guessing, pretty much anyway. I do know that if I raise the rear/middle legs to get the tires off the ground, and introduce a bit of tilt, the legs in front will also tilt. So I think they can interact with each other, but both together cannot increase or decrease in height. It would have to be one increase, and one decrease. That's probably about as clear as mud.

I just can't see them "interacting" with each other. All of the hydraulic fluid that reaches the front legs come through the Hydac that is located on the curbside leg and unless there would be an issue with leakage, or the internal spring not holding the spool in the sealed position, there is just not anywhere for the fluid to go from one to the other leg. I guess it will just have to be a mystery for now.

 

[Scott'n'Wendy]

So I think they can interact with each other, but both together cannot increase or decrease in height. It would have to be one increase, and one decrease. That's probably about as clear as mud.

Yup. Especially since you are trying to identify a leak, you have to accept that any valve or cylinder could be leaking by causing behavior that is not normal.

 

[coglesby]

If I get the time this weekend I’ll check bypass on the leveling jacks and the valves for them. Pretty sure the LG is fine. I’ll let you guys know what I find when I get it done

 

[coglesby]

I don't know, since the legs are interconnected, it might be possible for excess pressure, from increased weight on one could bleed into the other leg. But I really am just guessing, pretty much anyway. I do know that if I raise the rear/middle legs to get the tires off the ground, and introduce a bit of tilt, the legs in front will also tilt. So I think they can interact with each other, but both together cannot increase or decrease in height. It would have to be one increase, and one decrease. That's probably about as clear as mud.

I’ve learned the landing gear legs will just follow the tilt of the trailer. The fluid just moves between the two. They only change the front to back tilt. Basically it’s a three legged stool.

 

[Scott'n'Wendy]

Basically it’s a three legged stool.

Never heard it said like that...but true.

 

[coglesby]

And the leg is halfway between the jacks that are tied together. Front LG, right rear, left rear.

 

[triplethreat]

And the leg is halfway between the jacks that are tied together. Front LG, right rear, left rear.

What does that statement mean.....I don't understand what you are trying to say.

 

[coglesby]

Let’s use the landing gear as an example. When the trailer shifts left or right, the landing gear will follow. If shifting right, the right landing gear will drop and the left will rise to equalize the weight with fluid moving between the two. The pivot point is halfway between the landing gears. That pivot point is one leg of the stool.

 

[triplethreat]

I'm going to attempt to explain what is happening under a Normal operation of the legs, which means that there is no valve leakage internally, no hoses leaking externally, and a totally normal operation that is working as designed by Lippert for this system. I made a crude drawing (excuse my lack of artistic ability here please) of the landing gear legs, hydac valve that allows them to work, and so on.


So in the picture above, when the front legs are being signaled to extend, the pump motor starts and runs in a CCW rotation. At the same time, the Hydac valve on the curbside leg will actuate, thus opening and allowing the pressurized hydraulic fluid to flow into the curbside and street side front legs. The curbside leg will start down (extending) because the line is hooked there first. Once that leg is "grounded", the resistance to the flow is less, over on the streetside leg because it has basically no resistance...vs. the curbside leg which is grounded. Once BOTH legs are grounded, the front of the trailer will start to raise and will continue to do so as long as you are pushing the raise button or until the cylinders reach the end of their stroke. So if we stop the raising let's say, in the middle of the stroke, or half of the ram extension from the cylinders....the pump stops running, the Hydac valve closes, and none of the pressurized fluid on the extend side of the cylinders can go back towards the pump, because the Hydac valve is closed.

While all of that is going on, the fluid in the cylinders that is BELOW the ram in each cylinder, has to go somewhere, because the ram is being forced down (leg extension), which means there is less area in the part of the cylinder BELOW the ram. That fluid is forced to the Retract Valve Block, which in turn is connected to the pump's "return" port. When all movement on the legs stop, the pump is no longer running, the Hydac valve on the curbside leg is closed and sealed off, and the fluid that has been forced back to the pump's return port (via the Retract Valve Block), cannot go anywhere because the pump is not moving. So basically all the fluid in the front legs are "Locked" where it is at.

The weight of the front part of the trailer, being put on the front legs is "trying" to force that fluid that is below the ram inside the cylinder, to push the ram back up, but the Hydak is closed and the fluid on top of the ram cannot be displaced because it has no where to go when the Hydac is closed. So that same front trailer weight is also trying to push the ram back up and use the "return" line of the cylinder to push the fluid back to the Retract Valve Block and then on to the pump itself...but that cannot happen either because the pump is NOT turning and it can't flow back into the reservoir....so again, the fluid in that hydraulic circuit is LOCKED in place.

The above explanation, as I stated in the beginning, is assuming that all components of the system are working correctly and there is no leakage issues either internally with the valving or the cylinders, or any external leaking like hoses, connectors, etc This is how I'm seeing the system work, if anyone has a better explanation or knowledge of hydraulics that can correct me if I have misspoke of am thinking the wrong way about this........PLEASE Chime in....

 

[coglesby]

When static (not moving) and no load on the cylinders (like when they are halfway up) the force on each side of the cylinder is equivalent but the pressure will not be because there is less volume on the bottom side due to the piston rod being in the cylinder.

 

[Hoopy Frood]

I'm going to attempt to explain what is happening under a Normal operation of the legs, which means that there is no valve leakage internally, no hoses leaking externally, and a totally normal operation that is working as designed by Lippert for this system. I made a crude drawing (excuse my lack of artistic ability here please) of the landing gear legs, hydac valve that allows them to work, and so on.
View attachment 50750

So in the picture above, when the front legs are being signaled to extend, the pump motor starts and runs in a CCW rotation. At the same time, the Hydac valve on the curbside leg will actuate, thus opening and allowing the pressurized hydraulic fluid to flow into the curbside and street side front legs. The curbside leg will start down (extending) because the line is hooked there first. Once that leg is "grounded", the resistance to the flow is less, over on the streetside leg because it has basically no resistance...vs. the curbside leg which is grounded. Once BOTH legs are grounded, the front of the trailer will start to raise and will continue to do so as long as you are pushing the raise button or until the cylinders reach the end of their stroke. So if we stop the raising let's say, in the middle of the stroke, or half of the ram extension from the cylinders....the pump stops running, the Hydac valve closes, and none of the pressurized fluid on the extend side of the cylinders can go back towards the pump, because the Hydac valve is closed.

While all of that is going on, the fluid in the cylinders that is BELOW the ram in each cylinder, has to go somewhere, because the ram is being forced down (leg extension), which means there is less area in the part of the cylinder BELOW the ram. That fluid is forced to the Retract Valve Block, which in turn is connected to the pump's "return" port. When all movement on the legs stop, the pump is no longer running, the Hydac valve on the curbside leg is closed and sealed off, and the fluid that has been forced back to the pump's return port (via the Retract Valve Block), cannot go anywhere because the pump is not moving. So basically all the fluid in the front legs are "Locked" where it is at.

The weight of the front part of the trailer, being put on the front legs is "trying" to force that fluid that is below the ram inside the cylinder, to push the ram back up, but the Hydak is closed and the fluid on top of the ram cannot be displaced because it has no where to go when the Hydac is closed. So that same front trailer weight is also trying to push the ram back up and use the "return" line of the cylinder to push the fluid back to the Retract Valve Block and then on to the pump itself...but that cannot happen either because the pump is NOT turning and it can't flow back into the reservoir....so again, the fluid in that hydraulic circuit is LOCKED in place.

The above explanation, as I stated in the beginning, is assuming that all components of the system are working correctly and there is no leakage issues either internally with the valving or the cylinders, or any external leaking like hoses, connectors, etc This is how I'm seeing the system work, if anyone has a better explanation or knowledge of hydraulics that can correct me if I have misspoke of am thinking the wrong way about this........PLEASE Chime in....

I think that is pretty much the way it works...except there is no one way valve between the cylinders to prevent movement of fluid between the legs. Unless each leg is connected to the manifold, there would be nothing to keep fluid from moving between the legs. Kind of like they are "wired" in series, so fluid is forced into one cylinder and then the other one. I believe it works both ways: Extend and Retract.

 

[triplethreat]

=coglesby;524607]When static (not moving) and no load on the cylinders (like when they are halfway up) the force on each side of the cylinder is equivalent but the pressure will not be because there is less volume on the bottom side due to the piston rod being in the cylinder.

I don't think the discussion was ever about "no load" on the cylinders. In a "normal" operation, the legs are either fully retracted and ready for travel, or they are extended and grounded and supporting the weight of the front of the trailer. When they are extended and grounded and holding the weight of the trailer, there is pressure on both sides of the ram. When that movement has stopped, and the front of the trailer is level or where you need it to be for hooking up, the fluid is "locked" into place because of what I mentioned above in my explanation.....Hydac closed and pump not running = no fluid movement.

 

[Hoopy Frood]

I don't think the discussion was ever about "no load" on the cylinders. In a "normal" operation, the legs are either fully retracted and ready for travel, or they are extended and grounded and supporting the weight of the front of the trailer. When they are extended and grounded and holding the weight of the trailer, there is pressure on both sides of the ram. When that movement has stopped, and the front of the trailer is level or where you need it to be for hooking up, the fluid is "locked" into place because of what I mentioned above in my explanation.....Hydac closed and pump not running = no fluid movement.

Yes, that's where we disagree. I think that there can be fluid interchange between the cylinders if the weight changes on one of the cylinders. But I do agree that it cannot bleed back into the reservoir. To me free flow between, just between the cylinders, explains why the pump only pumps to one cylinder and not both.