"Opening Restraints" Phenomenon

I actually have a Maintenance Manual for PTC trains from 1978. I dont have a scanner, but will try to get some pages scanned from the restraint system sometime this weekend. Having worked on the PTC trains with buzzbars, I can tell you that the system is actually pretty simple. *** Edited 9/29/2006 10:49:25 PM UTC by jd221***

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J7G3 said:
Hmm... I specifically remember watching the Demon - Great America Gurnee - run it's course with 4 harnesses open all the way. Back in the early 80's when they had the original thinner black harnesses. It looked funny.

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That could have easily happened by just restarting the lift. The failsafe mechanism only stops the lift when the train is initially dispatched with the restraints unlocked. The lift can just be restarted after.

Of the failsafe could have been removed. :)

-Nate

I've had my lap bar pop open (and would not lock itself after!) on the last ride I through this would happen: Space Mountain at WDW. I know, sounds weird. It happened after the ride second drop (about halfway through the ride) and I just sat correctly and held on and everything was alright. When the train arrived in the unload area, when the cast members saw that my bar was already up, they made a face like "I just saw a ghost", asked me if everything was alright and called up to get the train removed!

The simple fact is that given a long enough time-frame, restraint failure is bound to happen. Nothing works 100% of the time... But I would assume restraints work 99.9999% of the time.

Gee, there is a lot of ignorance on display in this thread.

(Now before you crucify me, please note that I chose that word very carefully. Remember, the difference between ignorance and stupidity is that there is a cure for ignorance.)

Over on PointBuzz, there is an article which describes, based on the patent drawings, the mechanism that drives Top Thrill Dragster. Look for it here: http://www.pointbuzz.com/ttdtech.htm

The beginning of that article gives an introduction to hydraulics and to the concept of hydraulic accumulators, which is how the Dragster launch system works. The initial example, though, is an unpowered system using a hydraulic cylinder and a small accumulator. The example is the mechanism used for virtually all of Intamin's restraints (lap bars and shoulder bars), except that the restraint doubles the system.

Referring to the diagram on that page...
Normally, the spool valve (3) is preloaded by the spring (3a) and actuated by the solenoid (3b). But you can see that is the first point of failure. If the spring (3a) should fail, the valve could fail to return to its closed, unpowered state (as shown). Second, if anything should allow the check valve (2) to hold open, that would also allow the bar to fail. A respected ride engineer (not me!) has actually identified a potential failue scenario in which the diaphragm in the accumulator (4) fails, allowing its nitrogen precharge into the hydraulic lines, so that a nitrogen bubble could cause the check valve (2) to stick open or to chatter, allowing the bar to fail. It is unlikely to happen to a single system, and each seat typically has two separate systems, making such a failure even less likely. But that's a way it could happen.

There are only two rides I can think of where I have experienced a total restraint failure, and in both cases it was an all-mechanical single-locking-position lap bar. One was an all-mechanical PTC bar that failed to lock properly on a junior wood coaster, the other was an Arrow all-mechanical bar on an ancient Runaway Train. In both cases the bar wasn't latched completely to start with.

There are a couple of things you should keep in mind. First is that the release pedal, electrical connection or linkage on the bottom or side of the car is not the only way to release the restraint. There may be an internal mechanism that can bounce open or otherwise fail. Second, remember that just because a restraint pops open does not necessarily put you into mortal danger. Someone mentioned the Vekoma SLC and the fact that the shoulder bar can open quite a distance if the ratchet fails...consider this: the bar does not have to be snug tight to keep you contained within the ride. As long as the openings are closed enough to prevent an unintentional exit, you're still OK. Furthermore, most rides won't actually throw you even if the restraint fails completely. Some will, but most won't. And believe it or not, people who write standards for restraint performance are actually (finally!) beginning to take this fact into consideration.

Several people have suggested that I should add some mechanical details on restraint systems to my web site; I will keep that in mind this winter if I have some time to build some new content.

--Dave Althoff, Jr.
(who would have jumped in on this thread earlier, but was busy attending a conference which, among other things, was trying to establish restraint performance criteria for "family" rides...)

"unintentional exit"

I like that. :)

I can vouch for your last point having worked at a park where, no names here, certain folks rode rides sans restraints. Oh, and there were no unintentional exits.

One time, my B&M standard harness was stapled uncomfortably tightly, (which I didn't mind, because it at least means that the ops are paying close attention), and has the train went down the first drop, the restraint clicked out one but only one notch. I think that this was only because of the fact that the restraint was just barely locked into the click that it was in.

^ THAT is exactly what happened to me, on SFoG's Batman..."momentary terror". ;)

I have had my restraint unlock completely on Mantis near the very top of the lift. It was scary, but it relocked and stayed locked throughout the ride.

I dunno Rideman,when I had that restraint failure on ME it was certainly loose enough to the point where I could've slipped out rather easily.

Still I look forward to any updates you might be willing to make to your site to shed some light on how these systems function as that's always been somewhat of a fascination of mine.

You could have slipped out easily *if you wanted to*. The ride wouldn't necessarily throw you out, though. The restraint would still be in the way, you would still have to pull one arm back behind the bar, drop your head back, slide all the way over to one side, and finally drag your leg out from behind the bar. It's unlikely that you would extricate yourself from the various obstacles accidentally, though you could do so easily.

--Dave Althoff, Jr.

^True,but still the bar shouldn't just open up like that.It should remain closed & locked at all times during the ride.

On the intamin inverts they're smart enough to have the belt mounted on the side with very little slack instead of the front so that in case of a restraint failure it won't open up anywhere near as much as the SLC restraints will.