Through Wall Hydraulic Slides Moved While Unhitching

[Jlawles2]

The way the hydraulic slides work from my understanding is both cylinders are tied to extend together and retract together. This means there is only 1 line going back for each function and Tee's to both slides. Thus if it is a leaking cylinder then both COULD move. However it's stated that the slide moves when leveling the system. This leads me to think it's a valve in the block not a cylinder as movement only happened when the system was making fluid pressure.

Now if the slides were walking out during travel, I would tend to believe it could be a leaking valve.

Testing for an internal leak should not create any more of a hydraulic mess than changing a valve if thought out and done properly. Should the slide cylinders be tied extend and retract common between them, simply removing either of the main hoses at the valve block (say retract hose when fully extended) then pressurizing the system in the direction of the slides already full travel should cause 2 things: 1 - high pressure kick out and 2 - if there is a leak it will loose pressure and then bleed through the removed hose. simply bumping the correspondig button every xx seconds to determine if there is a leak will help facilitate in showing fluid return through the opposing side of the system.

Now if the tech were to AIR test the cylinders (air will leak through a much smaller defect than oil) that is an entirely different headache to deal with.

[TedS]

I believe the slides are independent, you can move one without moving the other by opening or closing the respective valves. The landing legs are tied together, one extends to contact the ground then the other extends to contact the ground(compensates for uneven ground).

[JBill9694]

TedS and Jlawles2 You are partly right, and partly wrong. The schematic provided by Ted is partly correct, except that I have one master block instead of several separate blocks. The procedure for testing a cylinder calls for actually disconnecting one of the hoses from the cylinder and then applying pressure through the remaining hose to see if any oil leaks past the internal seals. I did not get into the actual procedure with the mobile tech, but along with the chance of oil leaking past the seals there is also a need to purge the system of air afterwards. The man said that he wouldn't do this in the field due to concerns about containment and disposal and doesn't know of anyone who would, and I'm not going to second guess him.

Now, my meager understanding of the hydraulic operation is this: With one master block, once the on demand hydraulic pressure unit (HPU) kicks on there is pressure against all valves. Leakage past one valve, say the extend slides valve, can cause a movement until the pressure equalizes on both sides of the retract valve, which is why the slides don't extend all the way. When we extend the landing jacks using a single switch the curbside jack extends first to make contact with the ground, then the roadside. When we extend the stabilizing jacks using one switch the roadside front jack extends first followed by the roadside rear jack, then the curbside front and rear jacks. When we extend the slides using one switch the roadside slide moves out about 6", then the curbside slide extends fully, then the roadside slide extends fully. When not moving jacks or slides the HPU is off and pressure is static on both sides of the valves, with no leakage from the closed system there is not a pressure deferential that would cause something to move, so we can travel safely.

Since the problem did not reoccur during hitching and unhitching, I agree that there is likely contamination in the oil, which will likely mean putting the trailer in the shop. We are 6-months out from being back at our home base where we can be without our trailer for an extended period and still have a place to sleep. Until then I will be monitoring the problem and taken precautions such as blocking the slides in when traveling.

[Scott'n'Wendy]

When we extend the stabilizing jacks using one switch the roadside front jack extends first followed by the roadside rear jack, then the curbside front and rear jacks. When we extend the slides using one switch the roadside slide moves out about 6", then the curbside slide extends fully, then the roadside slide extends fully.

Interesting. Thanks for the description John. Is the slide operation way it always was since new? Like, that's the way it is intended to work?

[howson]

Scott'n'Wendy -- I know for the slides that JBill9694 's description is typical (I'm not familiar with the jack operation). The slide with the least resistance to the applied hydraulic pressure is the one that moves. Once the first slide is fully extended the other slide, now being the one with the least resistance, extends. As mentioned in other posts on this thread, there is a way to manually exclude either slide from extending by closing a valve on the manifold.

[Jlawles2]

JBill9694 John, With the reservoir being so small on for all of the operations, you may want to change it a couple of times, hopefully catching the debris. If you do find the debris, that may help tell someone where to start looking.

I would do at least 1 fluid change with everything retracted (should put the most oil in the tank). Ideally if you could re route the return line to a waste bucket and catch it as you close everything this would be your best chance to catch the offending debris as the pump is partly recycling the return oil from the cylinders as it enters the tank.

Once you figure out what it takes to drain the tank, it should be fairly quick with the size of the tank. You could do the drain and refill either when planning to leave or when you get to the next location before setup. For the first one, I would start with it while parked and everything extended (easiest to tinker and figure out how to do it when not pressured to hit the road or get setup), then after the next cycle when everything is in, drain and refill again. this in theory should give you 15% or more fresh oil (speculation here since I do not have tank and cylinder information).

You could probably run the oil through a coffee filter to find the offending debris (also keeps you from digging around in the oil). If you do choose to do a return dump while filling the tank, after 2 dumps, filtering the oil and reusing may be a possibility (just depends on how much the system holds total not just the tank) to minimize expenses.

[TedS]

The description of the slide stopping after traveling a short distance could indicate there is air in the rod end of the cylinder and the slide stops after that air is compressed. Having now run the system many times has purged that air and the slide will no longer drift.

It's interesting how many functions are plumbed in parallel.

[Jlawles2]

The slide stopping part way out is due to the resistance of the slide. With 2 slides, which ever one is seeing the least resistance at the time will move. If the slides are similar to the ones in the 303, one is a straight out slide on rollers and the other is skids and at an angle. The angled one most likely moves out at the bottom only a few inches until the inside most part of the slide lowers and the slide is 100% on hydraulic move only, then the roller side slide (usually kitchen) now freely rolls out until fully extended, and the other slide starts moving again.

Hydraulics are like plumbing, the fluid will take the path of least resistance when in common grouping.

[JBill9694]

The way I described the operation of the jacks and slides in post Plumbing is how they have behaved from the start. I believe that there is another thread on the forum somewhere that describes pretty much the same thing. Now, how the system knows when to move which jack/slide is beyond my knowledge level, but it probably has a lot to do with pressure and the level sensors (at least for the jacks). I don't believe there is air in the line that would cause this consistent behavior. Not after closing in on 5 years of full-time use.

The hydraulic system is a closed system, in that oil does not really fill or empty from or to the reservoir during normal operation. As oil is pumped into the top or bottom or a cylinder, it flows out of the opposite side at an equal rate. Thus, the level in the reservoir remains fairly consent. I've checked the oil reservoir with everything retracted, and with slides extended and landing and stabilizing jacks at various lengths of extension, depending on how level the pad is, and can confirm that the oil level in the reservoir remains unchanged.

As I noted at the start of this thread, I do have some experience with the inspection of large hydraulic gates. Hydraulic oil was never emptied into the gate system directly from the shipping container. It was always run through a series of filters. Whether this is standard procedure for smaller systems, I don't know. Even if it isn't, there are the issues of disposal of the old oil and purging of air from the system (it's not like the cylinders have bleeder valves like on the old brake systems). It is also on my list to call Lippert this coming week and see if they have any recommendations on whether to change or filter the oil.

And then there is the real issue, keeping SWMBO happy while addressing the issue. Instead running jacks up and down and slides in and out while living in the trailer, it will be much better for our marital bliss to wait until we are someplace where we can stay with relatives while this is being done.

[Scott'n'Wendy]

I believe there is nothing for you to do now other than schedule a fluid change at a convenient time. I'd get a spare to carry...if you get one..you will never need it..but if you don't have one......
I don't believe you have air pockets either, if your slide kind of bounced or pulsed on the way in or out..that would be air in my opinion.

This thread has made me curious how the stabilizing jacks work for levelling. If there are no wires to the jacks, there must be a nifty hydraulic valve at the jacks. Nothing to do with this thread...but I'm curious.

[Jlawles2]

JBill9694 John, I would suspect a small amount of fluid change in the tank. With everything retracted, you have the rod volume difference from when extended. Fluid level changes are much more dramatic as rod diameter approaches bore diameter of the rams (typically in higher force applications).

I would probably be willing to put money on it that if you mark the tank with everything in, then with it leveled and everything out, there is a difference. Since most people do not check the tank when hooked to the truck with everything up and in, they never see the "FULL" volume of the tank.

[TedS]

Head end volume is always greater than rod end volume per stroke on these single-rod double-acting cylinders. Fully extended cylinders will take more oil than fully retracted cylinders. A common ratio is 2:1.

[JBill9694]

Jlawles2 and TedS . Can't argue with your reasoning. All I can do is reiterate that there is not a noticeable difference in the reservoir level between everything retracted and everything extended. And yes, Joe, I do have a reference mark on the reservoir. But I could also be wrong, it has happened before and it has been a while since I actually checked the reservoir with everything retracted. Our next move is Wednesday, so I'll try to get before and after pics of the reservoir when we hook up. Maybe I better write myself a stinking note?

[JBill9694]

Tuesday, I called Lippert and talked to Brett G. who concurred with the diagnosis of contamination of the hydraulic fluid. Brett provided the attached documents and, as stated in the documents, said that the hydraulic fluid should be changed every 5 years. Review of these documents confirm my suspicion that the oil change and purging is not something I want to do without the proper facilities and equipment. Don't think the RV parks we will be staying in would be too happy about it either. I did do the visual inspection of the fluid in the reservoir and did not see any obvious contamination.

Wednesday was moving day (no problems with tear down, travel, or set up) and as promised I took pictures of the reservoir with jacks and slides extended and retracted. Jlawles2 and TedS were right to call out my diatribe in post 39 and I stand corrected. There was a 2 1/2" change in fluid level. I'm sure that some of you will note that the fluid level with the everything retracted is not to the recommended fill line on the top sticker. My memory on this is clear, I asked about the fluid level after our shakedown cruise almost 5 years ago, and was told by the techs that this is as full as the reservoir needs to be.

Also, there was a previous comment about the size of the tank being small, based on this single data point there is almost three times the required fluid in reserve with the everything extended. This will change with how far the jacks need to be deployed for level.

[Jlawles2]

JBill9694 John, I think they call it the "HOOT METHOD" where you remove the return line and plumb it to a bucket, fill the reservoir to the proper level, then extend everything while continuously checking the level of the tank. Repeat as required until desired fluid color is achieved. This usually requires at least 25% more fluid than in the system.

You could (probably a much cleaner alternative) use a syringe to suck out as much fluid as possible from the tank, the top back off. Next time you move, repeat. I use a https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1 for doing the PS and brake fluids on the truck. If needed the syringe can be used as a funnel. Usually I just suck XXX out keeping note of the amount on the side adding them together until I can get no more, then using the same syringe I suck up and push the same amount back into the system. Again, this is probably a much cleaner method as you are only dealing with the syringe and the 2 buckets not worrying about how hard the pump will push the fluid out. It will take several moves but the fluid does eventually get changed.