Slide Seals

[travelite]

Folks, there's a gentleman on the other site who suffered a slide air seal failure. Turns out the Prevost parts cost for the seal is $3400.00. Earlier this year I had DMRV, Donnie Myers, replace the slide seals on my H3 Vantare. As you probably know Vantare uses a non-pressurized bulb-style seal and there's an inner and an outer seal per slide, four seals in total. The total parts cost for all the seals for my coach, both livingroom and bedroom slide, inner and outer, was $395.16. My Wanderlodge had a pressurized air seal on it's livingroom slide so I'm very familiar with their cost and function. I have to wonder why Prevost hasn't changed course to a Vantare compression style beyond the obvious profit factor; Wanderlodge did change in their very latest coach, the M450LXi? I've never heard of any of the M450LXi owners have slide seal issues. Airliners use the pressurized style because they work well with the pressure differentials at 35000 ft. That's the only advantage to the pressurized seal that I'm aware of and its an advantage that doesn't help us. Thoughts?

[dale farley]

David,

I replaced both the seals on my slide for $227. I ordered the seals straight from the manufacturer and did the work myself. I would really hate to have to spend $3400 for a seal. The labor may cost more than the materials, but we've had some members do the replacement of the air seals themselves with some help and moral support from other Poggers.

[travelite]

Thanks Dale,

I designed the air seal used in my Wanderlodge LXi and I had a manufacturer produce it for me; I did the living room and bedroom seals for both the LXi and the LX. I made them available to the Wanderlodge community free. The driving issue was the failure rate, unavailability, and the expense of the HWH seal. My seal was made of a better material, with a slightly thicker cross section which made it more durable, and a customized profile for our Wanderlodge application. I have to refute the idea that slide seals allow looser slide body to coach body tolerances, and that they allow Prevost to imprecisely make the body cutout and to imprecisely center the slide body within the cutout. There's a couple of issues. First, like Newell and Wanderlodge, Prevost uses a radial-in air seal which means that the seal expands inward towards the slide body. This is the toughest configuration to work with. The problem is the corners. Given an air seal's cross section profile and dimension, the seal will be able to expand to only a given stroke. The stroke should be larger than the gap between the slide body and the coach cutout or you won't achieve a seal. This is simple enough in the linear case but in a corner the amount of stroke is greatly reduced and is related to the at-rest thickness of the air bladder and the center line radius (clr) of the corner. At a minimum, the clr of the corner needs to be 8x (or more) of the relaxed height of the seal, so a seal of 1/2" height needs a minimum clr of 4" and preferably more, and even then the stroke of the seal can only achieve a fraction of its spec without buckling. What this means is you need a long sweeping curve at the corners and you need a tight spacing to fill. Loose tolerances won't do or the slide seal will buckle at the corners creating a void for water to enter. Another problem is the long distances that the Prevost seal needs to span. With a slide body in excess of 14' there's the problem of the air seal exerting opposing forces on the coach and slide surfaces. This causes a bow in both surfaces and requires the addition of structural bracing and clamping. Imagine a 10psi seal contacting the body across a 14' span 1" thick, that's a force of 1680lb, which causes the surfaces to bow which may result in spacing that the seal can't fill, again another reason why spacing or centering tolerances cannot be sloppy with pressurized air seals. Having said all this, it can be done and it is done, but I have to ask why? Virtually the entire industry uses Vantare style bulb-seals and with great success. They're easy to replace, cost virtually nothing in comparison, require no complex air systems, and they do work. I've been in torrential downpours in my Vantare and have inspected the entire circumference of both slides and have not found any leakage. True, there's a flange that you need to have on the exterior and interior slide bodywork to make contact with the compression seal. Well, that flange can be made to be barely visible as shown in the attached Wanderlodge M450LXi pic; and it's a tradeoff I think many of us are willing to endure. I can appreciate the air seal, but for those who need to park their buses unattended for a few days or weeks while they get on a plane to Europe, they had better have a 100% reliable source of compressed air and they better hope that they're air seal doesn't experience a sudden rupture or they're going to return to a world of hurt. I predict, with the increased use of slides in Prevost stagecoaches, these folks aren't going to put up with these issues and Prevost will eventually move away from the pressurized seal. Maybe wishful thinking!

13715

[Gil_J]

The marketeers have done a great job of marketing the frameless slide. They sure look great, don't they? I too like the appearance better, but really was never dissatisfied with the framed look, especially the recessed frames.

The active air seal is a great idea. I designed a specialized communications trailer once and the winning bidder used an air seal on the slide. The problem with air seals is they pretty much require the vehicle to be stored indoors when unoccupied and when in use the owner has to monitor the seal unless the control system includes a pressure alerting capability. I saw the inside of a coach that had all fabric and foam changed out due to mold from a seal or aiur pump failure. This cost well into the 6 figures. The coach was left unattended on the owner's campsite for a couple months. Whether the slides are kept in our out, a seal failure provides a path for water intrusion.

I'm not sure why I hear of so many seal failures. If properly designed, the seal and air supply control system, there is little to cause a failure. I suspect the biggest concern is debris resting between the seal and slide. Even sand could be a problem for a moving coach's seal. When in motion there a possibility of abrasion to the seal as it rubs the slide as the slide moves. Slide movement needs to be limited when in motion. This is likely controlled with tight slide roller tolerances and the safety pins.


I don't know if this is a newer HWH air seal, but the motion of this seal appears well designed (Click here (http://www.hwhcorp.com/airseals3.html)) and then watch the video. Here you can see a uniform motion of the seal when inflated and a pull back when deflated. This seal, like Prevost's, doesn't look cheap though.

I guess air seals could simply be replaced every 4 or 5 years. I know at least one owner that routinely throws good stuff away well before they would likely fail. Unless it's a safety system I don't recommend these aggressive and costly replacement practices.

[travelite]

It is comical Gil, we have this streamlined bus body that suddenly becomes very awkward looking when we extend our slides. We have these two ungainly room warts hanging out the side of this otherwise beautiful bus, but it's okay as long as we have a frameless slide body design? The bus body lines are shot when the slides are extended so who cares! As long as the bus regains it's form when the slides are retracted. Here's my bus with the slides retracted. Can you tell there are slides there? Nope. Same with the Wanderlodge M450LXi. The recessed slide flanges look great.

Very true. It is pure marketing and the joke is on us. We simply can't leave these buses unattended and exposed to the elements. There needs to be some seal redundancy. If the air seal fails there needs to be a backup seal to at least make an attempt to keep out the elements. This is where a non-pressurized seal shines. Bulb seals can become punctured and tattered and they still work. They have built-in redundancy characteristics. How many of us have replaced the door seals on our 10 to 15 year old cars? I bet not many. They may be cracked and punctured but they're still sealing. I think we hear about pressurized seal failures because a single puncture renders them useless. Oh, and forget fixing them with a bicycle patch kit. These kits won't adhere to EPDM. I do fault Prevost's choice and design.

I enjoyed the HWH video. That seal is very similar to the one I did. Mine incorporated a bead on top similar to this new HWH design. The video is a little misleading however. When I was experimenting with my design I found I could inflate it thru a corner as long as the slide body was missing, but as soon as I inflated the seal against the slide body it kinked. These long stroke seals will sometimes hang up on the opposing slide body wall and kink while inflating. I had to take steps to pre-form the corners to prevent kinking.

Yes, for anyone who falls for the "zeroing-out" philosophy, slide seals need to be a part of this too. Figure $3400 per seal plus $1000 for the install times two, for a grand total of $9000, and do it again in 5 years! :)

137161371713718