28 replies to this topic

[Kicking Horse]

Here is a quote from the Colorado Tramway Board Rules

Quote

the service brake shall not open prior to the drive system developing sufficient torque to prevent overhauling.

What does that mean?

:help:

[highspeedquad]

It sounds like that means that the brake can't open until the engine gets enough power so that it doesn't roll back. But don't hold me to that, that's my translation. :help:

[Kicking Horse]

that's what i think too but i want a lift techie to awsner. :)

[liftmech]

That is what it means. Overhauling is what engineers use to describe the unpowered movement of a lift in either direction, forward or backward. Most lifts, except those designed to go backward, have a backstop in the gearbox which prevents the lift from accelerating backward when the service brake opens.

[Allan]

The z98 separates the two... Rollback is the unintended reverse movement of a lift, while overhauling is the unintended forward movement of the lift. So an overhauling load would be a load that is capable of making the llift move forward, such as more people on the downhill side than on the uphill. So the tramway rule for us would mean that the drive must build enough torque to be able to control a full downhill load before releasing the brake. (Also called torque proving, or proof of torque). This torque proving also works the other way - the drive must prove that it has enough torque to not allow a fully loaded lift to roll back. On (some) older lifts, there was no such thing - such as the Red chair - which releases the brake as soon as the start button is pressed leaving the load on the rollback devices.

[highspeedquad]

So that, along with the sheave load, is what determines if a lift can download or not and at what capacity, correct?

[Outback]

Allan, on Feb 21 2005, 08:52 AM, said:

The z98 separates the two... Rollback is the unintended reverse movement of a lift, while overhauling is the unintended forward movement of the lift.  So an overhauling load would be a load that is capable of making the llift move forward, such as more people on the downhill side than on the uphill.  So the tramway rule for us would mean that the drive must build enough torque to be able to control a full downhill load before releasing the brake. (Also called torque proving, or proof of torque).  This torque proving also works the other way - the drive must prove that it has enough torque to not allow a fully loaded lift to roll back.  On (some) older lifts, there was no such thing - such as the Red chair - which releases the brake as soon as the start button is pressed leaving the load on the rollback devices.
<{POST_SNAPBACK}>

Perfect explanation Allan!

[liftmech]

highspeedquad, on Feb 21 2005, 10:00 AM, said:

So that, along with the sheave load, is what determines if a lift can download or not and at what capacity, correct?
<{POST_SNAPBACK}>

Yes. You can tell, to a certain degree, whether a lift has a download capacity by looking at the sheaves on the light side. A tower with eight on the heavy side and two on the light side probably is not intended to download.

Old F-lift actually had to have a Jake brake on its diesel because it was intended for 100% downloading and the diesel's unaided compression wasn't high enough.

[highspeedquad]

I have seen lifts that have those towers where there is only one set of sheaves, for the uphill side. You can really tell that those are not designed for downloading.

[Kicking Horse]

Another Quote from the tramway rules.

Quote

The Failure of one braking system to properly decelerate the aerial lift shall automatically initate a second braking system, if any.

I thought all lifts are suppose to have 3 different brakes?

In fact the it says the aerial lift shall have the following friction type brakes

Service Brake
Drive Sheeave Brake
Rollback Device

I see that as 3 different brake systems?


I'm puzzled

[Allan]

Here's the info on that... Again, from the Z98 - so it may be totally different.

A lift that is self braking (decelerates, stops and remains stopped withing the service braking distances) does not require a service brake or rollback brake, but does need an E-Brake.

A lift that will not accelerate in either direction when not driven, but is not self braking requires a service brake, and e-brake but no rollback brake.

A lift that will accelerate in the reverse direction when not driven requires a service brake, e-brake and rollback brake.

A lift that will accelerate in the forward direction when not driven requires a Service Brake, E-Brake and another Retarding device. I don't know what the other retarding devices are though.

[Kicking Horse]

Allen is the there a copy of the z98 on the internet somewhere?

[Allan]

Nope - well you can buy a copy from the csa.ca website for $99 last time I looked.

[Kicking Horse]

ok. here is another one

Quote

The Rate of the carrier's acceleration to and deceleration from, the design rope speed shall not exceed eight (8) feet per second squared (2.4 meters per second squared) under the most unfavorable braking condition.

what does that mean? :help:

[highspeedquad]

I think that it means that the carriers must not speed up at speeds of more than 8 ft or 2.4 m per second in the worst braking situation. I do think that we need a techie for this one.

[vons]

This is for detachable lifts it is simply the max accel/deccel for the carrier in terminal from line. So when you chair enters the terminal it cannot slow down faster than 8 f/s^2 and when you load it cannot accelerate faster than 8f/s^2

[highspeedquad]

Okay, that makes more sense. What does it mean by the squared thing?

[liftmech]

In physics motion is represented by (x) squared to show the fact that there are two dimensions, time and distance, in the equations. Consider that you have a mass sitting still. The law of inertia says that it will resist being forced into motion, so you have to keep the accelerating force down to aviod jerking that mass (you, sitting on the chair) around. Movement in forward direction is one dimension, time required to move is the other. The same applies to braking. Once the mass is in motion, the law of inertia says that it will want to remain moving. This is why you feel like you're going to go through the windshield of your car when you hit the brakes hard. Stopping distances are calculated in the US using the equation (V squared)/8000, where V is velocity or speed of the lift. The numbers generated by this equation give you the parameters for setting your brakes up. On a fixed double or triple, where full line speed is 500 FPM, this equation gives you a maximum stopping distance of 31'3". Minimum distance is 20', because anything less than that causes sever chair swing. I forget the equation used to figure that out.

[Duck]

Acceleration. Rate of change!

In each second, the velocity of the carrier may not vary by more than 2.4 metres per second.

We'll use v2 = v1 + (a * t).

v2 (final velocity): line speed
v1 (inital velocity): initial speed in terminal
a (acceleration): our rate of change of speed or velocity
t (time): what we'll solve for to find out what the min. amount of time to accelerate from terminal to line speed is

So, let's say:

v2: 5 m/s
v1: 0.5 m/s
a: 2.4 m/s/s

v2 = v1 + (a * t)

5 m/s = 0.5 m/s + (2.4 m/s/s * t)
4.5 m/s = 2.4 m/s/s * t
t = (4.5 m/s) / (2.4 m/s/s)
t = 1.875 s

So, the minimum time to accelerate from 0.5 m/s (terminal speed) to 5.0 m/s (line speed), according to this regulation, is 1.875 seconds.

-Iain

[Duck]

liftmech said:

In physics motion is represented by (x) squared to show the fact that there are two dimensions, time and distance, in the equations.

Speed is expressed as a factor of time and distance. A vector is speed with direction. A vector (or speed) with two time components (m/s/s, or m/s^2) represents acceleration, or rate of change of speed. It of course doesn't matter what unit of distance or time you use (hours, years, millimetres, etc.).

liftmech said:

On a fixed double or triple, where full line speed is 500 FPM, this equation gives you a maximum stopping distance of 31'3". Minimum distance is 20', because anything less than that causes sever chair swing. I forget the equation used to figure that out.

d = ((v1 + v2)/2) * t

d = 6.1 m
v1 = 2.5 m/s
v2 = 0

6.1 m = ((2.5 m/s + 0 m/s)/2) * t
6.1 m = 1.25 m/s * t
t = 4.88 s

Thus the minimum stop time is about 5 seconds.

-Iain