11 replies to this topic

[Lift Kid]

Hey everyone! I have some questions about sheaves. First question, tell me more about drop sheaves! I have seen a ton of topics on this forum about em'. I know that they're heavy, painted red, made from steel, etc. But what is their true purpose? (diagrams would be a huge help) Next, I've heard about sheaves that reduce static electricity build-up. What are they called? What do they look like? How do they work? (again, pics and diagrams help) Also, what is the technical name of the sheaves inside of the terminals of a detach? (the ones that act as the PTO) Anything else that forum readers should know about sheaves perhaps could be included in this topic as well. Thanks!

And yes, I have searched the forum and have not found exactly what I'm looking for.

This post has been edited by Lift Kid: 26 October 2008 - 04:45 PM

[SuperRat]

Since I'm not quick with diagrams I'll tackle an easy one. In Doppel-Tec world the sheaves that act as a PTO are called PTO sheaves. The other sheaves in the terminal are called terminal sheaves, dampening sheaves and if the bullwheel is smaller than the line gauge there will be horizontal deflection sheaves. In the UNI-GS quad terminals I work on each side has (starting closest to the nearest tower) 3 dampening sheaves, 1 terminal sheave, 2 PTO sheaves and in our 2007 lift they included single horizontal sheave for maintaining coupling alignment as the bullwheel liner wears.

[Allan]

The drop sheaves are used to break the derail fork; as seen in the attached pic. On our new Doppelmayr the setup is a little different but achieves the same thing - a broken fork. On some lifts there are indeed special sheaves that take care of static buildup in the rope. YANs have copper lugs installed in two of the guide sheave liners. Our Doppelmayr T-Bar has bullwheel liners with conductive material in them, the Thiokol is supposed to have conductive guide sheave liners, and the Mueller has aluminum bullwheel liners.

Attached File(s)

•  Tower_2_Heavy_Side_01_19_07__5.JPG (706.35K)
  Number of downloads: 52

[Lift Dinosaur]

[quote name='Lift Kid' date='Oct 26 2008, 06:45 PM' post='79803']
First question, tell me more about drop sheaves! I have seen a ton of topics on this forum about em'. I know that they're heavy, painted red, made from steel, etc. But what is their true purpose?
The drop sheave is usually the #1 sheave on the assembly. It is mounted on a 2-pair bar and when the cable leaves the sheaves, the weight drops the pair bar which breaks the brittle bar deropement sensor and stops the lift. Leitner-Poma does not use this system as their brittle bar / cut wire deropement sensor is located in the cable catcher.

Next, I've heard about sheaves that reduce static electricity build-up. What are they called? What do they look like? How do they work?
They are generally refered to as "grounding sheaves" or "grounding liners". Variations are liners with copper plugs, or conductive materials included in the rubber liners as described by Allan. Their purpose is to disapate startic electricity that may build up in the haul rope. They probably don't look any different to you, except for the YAN guide sheaves which are usually painted RED
Also, what is the technical name of the sheaves inside of the terminals of a detach? (the ones that act as the PTO) Anything else that forum readers should know about sheaves perhaps could be included in this topic as well. Thanks!
Terminal sheaves are: entrance (or arrival) and exit (or departure) sheaves which hold the cable at the proper elevation to enter and exit the terminal. Next are the Power Take Off (PTO) sheaves which take the power generated by the moving cable and transfer the energy to: synchronization - acceleration/deceleration - arrival/departure mechanisms (That may seem confusing - that is different terminology used by various Manufacturers to describe the same equipment). These mechanisms have belts and pulleys (of different ratios) to slow the chair on arrival and accelerate it for departure. After the PTO's will be deviation / deflection sheaves which may be vertical or horizontal (or both) to alter the path of the rope from line gauge (width) to bullwheel guage (diameter)

Here's a picture of a PTO Assembly: PTO Sheaves in the Red box; PTO Belts in the Blue box; Accel / Decel pulleys and belts in the Green box; Accel/Decel tires in the Orange Box. The tires interact with the plate on top of the grip to slow down and speed up the carrier. (My best photo shop effort-sorry)
 PTO_Assembly_MarkUp.JPG (21.73K)
Number of downloads: 46

Clear as Mud??


Dino

This post has been edited by Lift Dinosaur: 27 October 2008 - 08:09 AM

[Lift Kid]

That all makes some sense. Thanks everyone! Now why does Doppelmayr continue to use the drop sheave system over having the sensor inside of the cable catcher?

I guess its a little off topic, but can't deropement detectors be electronic sensors v.s. brittle bars/break wires?

[Allan]

Lift Kid, on Oct 27 2008, 02:18 PM, said:

That all makes some sense. Thanks everyone! Now why does Doppelmayr continue to use the drop sheave system over having the sensor inside of the cable catcher?

I guess its a little off topic, but can't deropement detectors be electronic sensors v.s. brittle bars/break wires?

Our new Doppelmayr only has drop sheaves on the negative and combination assemblies - I would guess because you don't really know where the rope is going to end up in a full deropement. The support assemblies have the forks sticking out into the cable catcher.
Would a rope position detector be considered an electronic device? I believe high speed lifts require forks and RPDs? It may also have something to do with physically breaking the circuit.

[Lift Kid]

Allan, on Oct 27 2008, 07:14 PM, said:

Our new Doppelmayr only has drop sheaves on the negative and combination assemblies - I would guess because you don't really know where the rope is going to end up in a full deropement. The support assemblies have the forks sticking out into the cable catcher.
Would a rope position detector be considered an electronic device? I believe high speed lifts require forks and RPDs? It may also have something to do with physically breaking the circuit.

That all makes sense. I guess having something that physically breaks the circuit is considered more reliable.

Now, I thought I recalled RPD's were electronic or involved a magnet. How do those work on newer and older lifts?

[mikest2]

In the Z98 (Canadian code) you need a manually resetable tower switch, a prox switch does not satisfy that requirement, so break forks (Dopp) or cut wires (Poma) are used.

[Lift Dinosaur]

Lift Kid, on Oct 27 2008, 06:36 PM, said:

Now, I thought I recalled RPD's were electronic or involved a magnet. How do those work on newer and older lifts?

Proximity sensors (switches that detect the position of the rope in the sheave groove) made by Efector, Allen-Bradley and ??? are required by ANSI B77-1 2006 for lifts that run over 600 FPM. This is why most modern detachable lifts have a "Circuit One and Circuit Two". Circuit One being a Prox Sensor and a Brittle Bar/Break Fork and Circuit Two being a Break Fork only. This way if there is a failure of a Prox Switch (which is verified as a non deropement by area personnel) the lift can still be run at 600 FPM until the switch is repaired/replaced.
PRD's are not required on Fixed Grip lifts as they do not run over 600 FPM (even though some have them to advance safety)
Sparkys - feel free to jump in here anytime!!

Dino

[Lift Kid]

So how exactly does a PRD work? Magnetic perhaps?

[mikest2]

Lift Kid, on Oct 27 2008, 06:22 PM, said:

So how exactly does a PRD work? Magnetic perhaps?

http://www.pc-contro...k/Inductive.htm

[Lift Kid]

Very nice. Thanks for that.