The Secret Life of the Lift (Secret Life Of Machines Series 3 (1993) by Tim Hunkin)


Uploaded by Anjasomc on 12.01.2012

Transcript:
Boss: Don't do anything I wouldn't do!
[Jazzy music: 'The Russians Are Coming' - Val Bennett]
Tim: Today travelling by lift is completely taken for granted.
The experience though, of travelling at high speed in a completely sealed box,
propelled up and down by invisible machinery and often uncomfortably
close to complete strangers, can still be quite unsettling.
In this programme Rex and I are going to look at the history and workings of this slightly unnerving machine.
The basic idea of the lift is extremely simple.
You just need, er, a rope and a pulley.
Rex: Right Tim! Oy. Nooooow!
Tim: Simple gadgets like this have been used for lifting people for centuries.
But the problem is safety.
If the lady let go, her lover would plummet to the ground.
Particularly on building sites, riding up and down on unsuitable devices
was widespread until recently, despite the risks.
[construction noise]
The history of the lift, is really the history of making this sort of travel less dangerous.
Although at the time, no one seem too worried by this.
[construction noise]
All this changed in the mid-19th century, largely due to
an American engineer called Elisha Otis.
He added these teeth to the guide rails, and this ingenious mechanism to the lift itself,.
which locked into the teeth, if ever the rope went slack.
[ratchet noise]
Otis's idea was that if the person pulling the rope let go.
Or if the rope broke.
That the lift would automatically lock, and wouldn't fall.
To prove its safety he took it to the Great Exhibition in New York in 1853.
And performed daily demonstrations.
[sawing noise]
[clunk]
Despite the success of his invention, Otis himself had rather a tragic life.
He was a hard working, strict Presbyterian mechanic; who's enterprises kept failing.
[dragging wood, panting]
Tim: He started life running a saw mill.
[Otis drops wood]
Otis: Hmm, things look bad. I'll have to diversify.
Why don't I make something with all this wood I'm sawing up? [sawing wood]
Ah! That looks good!
Yeah! Who could resist this beautiful thing?
Oh, looks like everyone can.
Nevermind carriages, everyone needs to sleep don't they?
And I'll build one of those little contraptions to lower the bedsteads down to ground level.
Otis: Hey Mister, do you wanna buy a bed?
Man: Forget the bed buddy, can you make me one of those elevating contraptions? It looks very safe.
Tim: Otis's first commission resulted from an accident at a nearby factory.
Where a primitive lift had killed two men.
He never lived to see the success of his lift, dying of diphtheria while his company was still deeply in debt.
Otis: Diversification will be the death of me, Ohhh.
Tim: Otis's first lifts were all built to carry freight.
But in 1856 a department store called E. V. Horvalt commissioned a passenger lift. Advertised as a vertical railway.
It was gradually realised that lifts could enable developers to increase the height of their buildings.
Previously 5 storeys had been about the most anyone was prepared to climb.
Skyscrapers, like the Woolworths building in New York, finished in 1913,
had become totally dependent on their lifts.
One aspect of these lifts that caused alarm was the way that the car was supported.
In Otis's original lift, the rope was firmly fixed to a drum at the top.
But as buildings got higher there was more rope to wrap round.
and it started to get tangled.
By 1900 the end of the rope was normally being fixed to a large counterweight.
And merely passed over the drum at the top, gripping it by friction.
At first this seemed very daring, surely the rope might slip?
[clinking]
But in fact the friction of a rope passing over a pulley like this is considerable.
Capstan winches use this effect to lift enormous loads...
[motor noise] just wrapping the rope round once
although the capstan's completely smooth, I can lift Rex off the ground quite easily.
And as Capstans are normally used by wrapping a few times round
I can lift him off the ground with no effort at all.
Even wrapped around once, the friction is enough to stop a lift rope ever slipping.
Lifts still use this arrangement with the motor at the top and the
counterweight on one side and the lift itself on the other.
Once this idea of balancing the weight of the lift with a counterweight had been accepted,
it had the advantage that it greatly reduced the power needed to make the lift work.
I've added an extra 4 stone to balance my weight with Rex's exactly.
And er, we should now be able to go up and down quite effortlessly.
Tim: Okay ready? Rex: There we go!
Rex: Now my go!
Tim: Whoops. [Both giggle]
Rex: There you go... Tim: You going to hang on this time?
[rumbling noise]
Tim: Another major improvement, introduced in the 1890s, was wire rope.
Compared to the hemp rope used previously, it has incredible strength.
This is a testing rig for ropes. The rope is fixed in the steel frame and then pulled by an enormous hydraulic ram.
[whirring]
[bang] [bang] [bang]
This rope broke at a load of 124 tonnes. That's equivalent to supporting nearly 2000 people.
That means that each one of these wires could support 5 or 6 people before it breaks.
[jolly music]
As people started to accept the safety of lift travel.
Lifts became status symbols, particularly for hotels.
[music continues]
The basic design of lifts has changed little in the last 80 years.
And it's been realised they're an extraordinarily safe form of transport.
It's actually statistically safer travelling by lift than climbing the stairs.
This lift is supported by 7 ropes sharing the weight.
And each one of them is capable of carrying the whole lift by itself.
Even if they did all break, there's yet another safety device called the governor. [motor]
If this rotates just 10% too fast this disc starts to come out.
Catching this switch, turning off all the electrics.
If it goes slightly faster still, this whole disc locks up completely.
This pulls in wedges under the car, jamming it against the guide rails.
The modern equivalent of Otis's safety.
[whirring noise] [clunk]
This is the lift motor, it's connected via a brake and a gearbox [motor]
to the pulley drum and the cables. [motor switches off]
If all the electric fails, it's still just about possible to move the lift by hand.
So it's always possible to haul any passengers trapped inside to safety.
This is the Express Lift Company in Northampton, and this tower is where they test their lifts.
As buildings got higher, there was a demand for lifts to travel faster.
This motor powers a high speed lift that travels the whole height of the tower.
Speeding up a lift is quite simple, the motor is just connected directly to the pulleys without any gears in between to slow it down.
High speed lifts were first used in the Woolworth building in 1913 and they've changed very little ever since.
The only limitation on speed is comfort, which depends mainly on the car's acceleration.
If I stand on some weighing scales as I go down. My normal weight's about 10 stone.
My apparent weight should drop. Yeah there it goes,
...sort of instant dieting. If the acceleration was any greater I'd feel I'd left my stomach behind.
And then when it stops accelerating, my weight goes back to normal.
And finally when we get to the bottom and it decelerates,
my apparent weight should increase, sort of literally weighing me down.
There it goes.
Different countries tolerate different accelerations. [motor whirrs]
Japan the least, and Australia the most.
About 10 storeys is considered the maximum practical distance for a lift to accelerate.
And this effectively determines the maximum practical speed.
About 20 foot per second in this case.
Although the mechanical design of lifts has changed little in the last 80 years,
they did used to look rather different.
Like most lifts of the '20s this had no separate shaft.
It was built into an existing stairwell, all protected by this decorative steel mesh.
This lift would have originally have been worked by a full time operator.
The biggest change in lifts since the '20s has been to automate the control gear - removing the need for an operator.
This has been partly modernised now, but err originally both doors would have had to have been shut by hand.
Without an operator, it was easy to forget to close the doors when you left the lift,
and then the caretaker would have to climb up there and shut them before the lift would work again.
Then there was just a single control for up and down,
and needed some skill to stop the lift in exactly the right place.
New York was reduced to chaos in 1937 when the operators went on strike.
Voiceover: 2000 office buildings are affected, a million and a half New Yorkers are grounded.
The strikers object to a raised hourly pay rate, but a reduced work week. Result: less take-home pay.
A few inventive geniuses find ways to have business almost as usual.
But for the most perpendicular city in the world, an elevator strike is no laughing matter.
How would you like to walk up from Way Down There?
Tim: The key to automation was really the sensors. Some are simple switches,
this is a giant model of a microswitch. [clunk clunk]
[clunk clunk] It just switches these contacts on and off.
This is their actual size. This one's being used to stop the lift car from hitting the top.
[quiet clink]
Some sensors work without touching anything.
These were originally magic eye beams that switched whenever the beam was broken. [high-pitched beeping]
[beep and silence in time with light bulb on and off]
But today you don't usually see these, because they work with infrared.
this is a modern sensor, the light comes out of one side and is picked up on the other side.
So when it is pointed at a mirror it switches just as before when the beam is interrupted. [beeping noise]
[beep] [silence]
Well sensors like this are amazingly versatile,
I used one last year to detect the difference between the head of the coin and the tail.
I simply polished the head so it reflected the beam, but i didn't polish the tail.
[coin rattle]
[whirring] [coin clunk]
There are three separate sensors on the doors.
There's a beam across them.
There's a touch sensitive strip all down the edges.
And then there's an extra sensor that checks to see nothing gets squashed too hard in the middle.
The er, doors are actually worked by a motor that sits on top of the car.
In there. If I open this up...
Take off the lock... You can see the doors, the motor move.
And then there are extra sensors to confirm whether it's open or closed.
Finally there are sensors to detect the position of the lift, fixed to the top of the car.
The infra red beams are interrupted by these metal plates,
one set for each floor, to stop the car in the right place.
All these switches and sensors are connected to the motor room by wires dangling under the car.
The control gear has become extremely sophisticated.
There are several microprocessors in here, using the information from the sensors to the lift motor.
The control gear not only has to respond to all the switches and sensors in the car,
but it also has to manage where the lifts go.
This is a control simulator at Express Lifts, and it's currently being used to test the program
to work out the best way for a group of 4 lifts to answer a number of different calls.
So if for instance I set a call from the 12th floor.
I think this lift's going to answer it, the 3rd lift.
It's come down to the 12th floor, then I think the doors should open.
So then say the person that's got into that lift wants to go to the 7th floor.
And this, the doors should close again, and the lift should start going down.
Well if these lifts receive a whole lot of calls together.
Then the number of different possible combinations for the lifts to answer all these calls
quickly grows to hundreds and thousands. It's the microprocessor that decides the most efficient way to answer them all.
It has been found that people start to get impatient [footsteps]
if they have to wait more than 30 seconds for a lift to arrive.
[footsteps] Boss: Bother! Leave it Polly, it's stuck on 6.
Man: Here she comes now... Polly: It's gone straight past!
[footsteps] Boss: Don't fiddle with the button Joan, it won't make any difference.
Joan: Sorry.
Boss: If I'm late for my meeting, I'll... [watch ticking]
Tim: The more floors the lift has to serve, the longer the average waiting time.
[footsteps] [Ding!]
Man2: Ahem. Let me squeeze in here, eh Brenda? Brenda: Oooh! *giggles*
Tim: The only way to shorten it is to have more lifts.
This actually sets the maximum practical number of floors for a skyscraper, about 100. [footsteps] [lift dings]
Whereas a 10 storey building may only need one lift,
a 20 storey one needs two.
Continuing on up, the lifts would eventually leave no room for anything else.
[hydraulic pump noise]
Rex: Although modern lift controls have become more and more sophisticated
mechanically they've become much simpler and cheaper by using hydraulic power.
They've become much safer.
Like the device I'm standing on, which is merely a piston, tight fitting in a tube
and the hydraulic pressure pushes them apart, lifting me up.
Now if Tim pulls the pipe off... [water spraying]
I still descend: safely, and under control.
Cos the water can't come out any faster.
To make it even safer, Tim has now fitted a pressure release valve.
This still lifts me okay, but if Tim hangs on me...
It limits it, so there's no way you can overload the device.
[noises] [Tim sighs] [noise]
Tim: Hydraulic power has proved so effective, that it's now used on all kinds of machines.
[Diesel engine noise]
Hydraulic powered lifts are nothing new. They were first introduced in the 1870s,
and by the '20s had become a familiar prop in slapstick comedies.
[oriental music]
The lever opens a valve to let the water in and push the piston up.
Hydraulic lifts needed no electricity , working directly from the mains water supply.
Modern hydraulic lifts use oil instead of water, which keeps everything lubricated.
There's a reservoir in the basement, and the oil comes through this pipe
And it's fed into this enormous ram, that goes 80 feet down into the ground.
6 storeys is about the maximum for a single ram. [machinery humming]
And this sort of lift uses more power than a conventional lift,
because there's no counterweight to balance the load.
But they're cheaper to build, easier to maintain, and they're considered
so safe they don't even have to be fitted with safeties on the car.
[Slow music] The risk of the lift car plummeting to the ground may be negligible
but there have always been other dangers.
[lift doors click open] One of the main reasons for people falling into lift shafts
was while trying to escape from cars stuck between floors.
Modern lifts have extra precautions to prevent this.
They have this extension underneath, or toe-guard to fill the gap.
[lift doors clank closed]
People also used to fall into the shaft after escaping through the hatch in the roof.
Erm. Modern lifts no longer have a hatch anywhere because it's been
realised that people are actually much safer trapped inside.
But these safety regulations do make lifts much more claustrophobic.
In fact they're sort of sensory deprivation chambers,
the only clue you've got where you are is the indicators.
[crackly film noise]
[lifts open and close]
[lift whirrs]
[high pitched wheee noise]
[lift whirrs]
[whee noise decreases in pitch]
Tim: It's not surprising that many people have phobias and fantasies about travelling in lifts... [ding]
[squashing noise] Joan: Oh! I can't breathe in here! Oh!
[ding] Man2: Polly, just you and me...
...In the garden of Eden *sleazy cackle*
[ding] Boss: Why's it stopped?!
[electrical crackle] This inefficiency drives me round the bend!
I refuse to be stuck in here! Let me out! Let me OUT! banging against lift walls]
[ding] Polly: Oooh.
[slurping and eating noises]
[Ding] Man: These women bosses, they're only after one thing!
My Body! Oh No! Miss Methias! Heeeelp!
[Ding] Brenda: *coughs*
[noise of smashing plasterboard]
Brenda: Oooh! My hero!
Brenda: So what's wrong with dreaming? [ding ding]
[ratchet noise] Tim: Perhaps Mr Otis's original lift did have its advantages.
You could always see exactly where you were, and look up at the safety for extra reassurance.
It travelled very slowly, and being completely open it it at least
left you with the feeling that you could escape if ever you needed to.
Anyway, I hope this programme's convinced you that however unnerving and disorientating
modern lift travel may feel, in fact the lifts themselves are actually incredibly safe machines.
Mission control voice: Five! Four! Three! Two! One! Zero! [hissing]
[boom] [roaring]
[Jazzy music: 'Take 5' - Dave Brubeck]