31 replies to this topic

[Allan]

For those who haven't seen them up close...

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[Allan]

Here's one in it's holder

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[KZ]

what do they do?

[Allan]

The one in the picture are to stop the lift in case the counterweight is lifted to high, basically if anything comes into contact with them, they break - causing the safety circuit to open and the lift to stop.

[KZ]

Cool. So its basically a sensor

[liftmech]

Technically, it's not, although for practical purposes that's what everyone calls them. A sensor is a type of switch that does not need to be replaced if the condition it is meant to sense happens. For example- some of you may have seen the GO switch located on towers, near guide sheaves, etc.- that's a magnet held in place by the presence of the haul rope. If the rope were to move away from the sensor, the magnet drops and trips the teeny little switch inside. A brittle bar is a glorified wire that, when broken, must be replaced- which can be a time-consuming job, depending on where the bar is. :P Doppelmayr loves the things.

[Emax]

Here's a different one. Securely mounts via molded-in magnets.

[Emax]

Jesus! Doesen't anyone want to know what's up with this thing?

This is a coup!! Simple parts doing a delicate job! What's wrong with you?


Major manufacturers have missed the point completely - here's the cure... for free!

[LiftTech]

Emax, on Aug 8 2007, 11:54 PM, said:

Jesus! Doesen't anyone want to know what's up with this thing?

This is a coup!! Simple parts doing a delicate job! What's wrong with you?
Major manufacturers have missed the point completely - here's the cure... for free!

Is it not the “RPD” out of its shell?

[FSJ]

Looks like a modified halogen bulb to me. Probably more UV resistant than a PC board.

[vons]

Doppelmayr loves brittle bars because I think they don't trust operators and would prefer a tech to examine the fault.
I am no electrician here but I will guess on Emax's proxy brittle tube, the device attracts itself to the rope, breaking on contact only when the rope wonders from a position over the center of the device to one of the magnetic ends. Emax tell me if I am full of it, Chuck

[Emax]

Actually, it's just a brittle bar - that is decidedly brittle. Halogen bulbs are used - because of their convenient shape. The magnets serve only to hold the assembly to the sheave train.

As you know, we have YAN lifts - and therefore we have DR-2s, DR-3s and DR-4s... very early "brittle bars". Inspections have revealed that:

1. Most of the bars have lost their "brittleness" - making them less likely to actually break the circuit when needed.
2. Many of the bars removed had glass-brittle insulation on the wire leads - much of which had broken away, leaving the two wires exposed. This happens at the entry point into the "boot" of the switch... where it cannot be easily seen.
3. Several of the switches with bared wires had those wires twisted so as to create a connection ahead of the switch - making the bar a bypassed device. This is really bad.

I have rebuilt all of the DR switches on all of our lifts - replacing the "boot" with a new one, using teflon insulated wire and a 2-pin connector about 2 inches from the switch. The teflon wire does not become brittle with exposure to UV radiation. The connector allows the switch to be changed out easily - without the need to pull yards of wire through the crossarm.

The rebuilds fix what was wrong... everything except the questionable "brittleness" of the thing. It seemed to me that if you really want brittle, use glass. Ever busted a light bulb without breaking the filament? The need to easily retrofit drove me to the magnets - you can place it anywhere and it will stay there. Halogen lamps come in a variety of lengths and are cheap if you shop well. The latest version of the halogen switch uses one lamp and one length of Garolite along side - for strength. These two are glued to the magnets (UV-cure adhesive) prior to a dip in 3M Scotchcoat and later in neoprene tool dip. The finished assembly is durable, easily mounted and has a very low profile. The profile is important because the original DR switches often get nicked by grip bolts in windy conditions. The lower profile eliminates this problem.

[vons]

let the brain wonder a but too much some times, comes with boredom

[liftmech]

FSJ, on Aug 9 2007, 09:23 AM, said:

Looks like a modified halogen bulb to me. Probably more UV resistant than a PC board.

We sprayed all your PC board-style brittle bars with black paint- well, actually Zop did- and that seemed to work for UV protection.

Emax- I asume you've got these in operation already? Do they work on other styles of assemblies, or just the Yans?

[Emax]

Some kind of coating is needed for the original DRs - I use a 3M Scotchcoat dip and then liquid neoprene. The addition of the connector sure helps.



Here's what happens to the original wires. This one was shorted at the point of entry. Can you say "bypassed switch"

[Emax]

Here's the final version of the "glass switch". Yes, they can be stuck (magnetic mounting) to any steel assembly.





After assembly, they're dipped first in Scotchcoat conformal coating and then in neoprene tool dip.

[lastchair_44]

Wow...not to get off topic but is he still working for you guys?

[Emax]

lastchair_44, on Aug 10 2007, 06:48 PM, said:

Wow...not to get off topic but is he still working for you guys?

Photo was shot this afternoon, so I guess so.

Garret is a pretty good "project guy".

[lastchair_44]

Yeah he is, tell him I said hi will ya?

[Emax]

Thread Title: "Closeup Of Brittle (break) Forks"

Technically, they're not "Brittle (break) Forks" - that's a colloquial term in the industry. They're properly called "frangible circuit elements" - things that break to interrupt a circuit.

"IN CASE OF EMERGENCY, BREAK GLASS" has adorned fire alarm systems for many years.

This post has been edited by Emax: 10 August 2007 - 05:30 PM