AVW Retractable Mitter fell on car

[Just Call Ben]

AVW is not super popular here in Southern California but not unheard of either. Recently one of my clients had a retractable mitter rack fall onto a car in the tunnel while in the wash cycle.

I inspected the design and they use a "half-globe" of UHMW sitting in a mating "half-dish" of the same material as a bushing for the orbital motion at each corner. There are four sets of these by which the entire rack is suspended allowing the unit to make a gentle circular motion over the vehicle.

One corner set was completely disintegrated after only 2 years in operation and two of the remaining three are in decrepit condition.

There is no backup washer to hold the rack in case of failure allowing the entire rack to fall down through its mount when the plastic bushing inevitably fails.

Has anyone experienced this? What do you think a proper solution would be going forward?

 

[Axxlrod]

The equipment is two years old?

 

[MC3033]

Solution would be preventative checks.

A safety that can be employed is using chain, wire rope or rope as a safety to strap up the mitter. Put enough slack so that the mitter can move around but not enough where the mitter can actually come down

 

[Just Call Ben]

The equipment is two years old?

Yes

 

[Earl Weiss]

I have AVW Mitters -9 currently (Not retractable) in operation for decades and never had this happen. After a decade or so noticed wear on the UHMW part and replaced. Can't help but wonder if some new batch was bad or there is a grit issue for some reason like reclaim. I think the safety chain or perhaps a large washer would be a simple solution.

 

[Just Call Ben]

I have AVW Mitters -9 currently (Not retractable) in operation for decades and never had this happen. After a decade or so noticed wear on the UHMW part and replaced. Can't help but wonder if some new batch was bad or there is a grit issue for some reason like reclaim. I think the safety chain or perhaps a large washer would be a simple solution.

No reclaim water is used in that section of the tunnel (polish stage).

 

[washnshine]

I hope nobody was hurt. I know the design very well - I was always surprised to hear this did not happen more often, especially since there is no backup support and the sole support system is also responsible for the oscillation. One other potential cause could be if the four UHMW components are not squared up and true, and do not evenly or squarely sit in the half - dish. That would put excessive and uneven strain and wear on these parts and I guess could happen in either manufacturing or installation. Again, I never heard of this happening before, but from seeing that design over the years I am surprised it does not happen more often. The Hanna oscillating shammy washers from the 1980’s and 1990’s used to have a similar oscillation and suspension/support design. If I remember correctly, the crank mechanism may have provided some back up in a failure, but probably would not have kept the whole thing from coming down. Simplicity in design is definitely good, but sometimes things can be too simple.

 

[Earl Weiss]

No reclaim water is used in that section of the tunnel (polish stage).

Well, on the one hand that would seem to eliminate that cause. On the other hand depending on Velocity of reclaim water I could see some grit being airborne and coming to land on the UHMW. Would not take much to have an effect after millions of revolutions. Does the soap solution for the mitter hit / lubricate these items as well? I know you said "Polish Section" but perhaps a difference is they are operating dry.

 

[washnshine]

I don’t think UHMW is UV tolerant - maybe a tunnel with glass walls or skylights could be problematic too. I think you may be able to get UV resistant versions of UHMW, but I don’t know if they use it for this component.