Update 1

• Preventive Maintenance?
• Generic Equipment
• Elevators and Doctors
• Hydraulic Cylinders
• How Fast Can We Go?

The concept of "Preventive Maintenance" has long been accepted in the elevator/escalator industry as an article of faith.

The idea is that by carrying out certain routine maintenance checks and procedures it is possible to reduce the incidence of call-backs and unscheduled shutdowns.

To quite an extent the idea of regular checks proceeded from the need to routinely oil and grease various parts of the elevator in the era prior to sealed bearings. Elevators in the first half of this century had a number of large bearings that required periodic greasing and checking.

There is very little need for regular lubrication on a modern elevator and the necessity for routine checking has been minimized by the use of more non-wearing parts. At one time the maintenance mechanic had to check controller contacts and clean them or replace them on a fairly regular basis. Today these contacts have to a large extent been replaced by solid state devices.

Of course each visit by an elevator mechanic to the site involves traveling time. In many cases the traveling time will exceed the time spent working on the elevator.

For all of these reasons the routine maintenance procedures have been called into question. More and more the major elevator companies are moving away from fixed time based maintenance. They are attempting to establish by means of historical data the life expectancy of components. With this information the possibility of "predictive" maintenance can be considered.

If the particular time at which a component will fail can be established then it is possible to replace it just prior to failure rather than replace it after failure.

Obviously this has advantages in reducing maintenance cost and increasing equipment reliability.

One of the difficulties with machinery reliability assessment - which is the first requisite of a predictive maintenance program - is the rather wide range of life expectancy of a given component.

It is apparent that the mean time between failure for any part is a function primarily of its actual use time rather than just calendar time. The common example is that of elevator lift cables. The life of these cables is generally considered to be proportional to the "mileage" on them. For this reason it makes sense to install a meter to record the running time or distance. Again, the life span of many components is directly related to the number of times an elevator starts and stops; thus it makes sense to install "trip" meters. The inputs from devices such as these then allow the maintenance contractor to determine when to replace components.

In the case of the elevator lift ropes, it is of course true that the mechanic could also check the ropes regularly foot by foot. This is a laborious procedure. In some cases the cost of checking ropes starts to approach the cost of replacing them. In cases such as this the advantage of predictive maintenance is quite apparent.

How effective are the various approaches to predictive maintenance? Too early to tell as yet. The jury is still out.

In any case, it is certain that the current trend towards predictive maintenance will continue.

The term "generic" equipment is used in the elevator business to denote equipment that is not manufactured by an elevator company but rather by a supplier to the elevator industry.

At one time, as with the Ford motor company, elevator companies such as Otis made virtually all of the elevator components from raw materials. They had foundries, machine shops, motor shops and all of the necessary factories to produce each piece of the elevator.

With the passage of time, this approach proved incompatible with the realities of modern manufacturing and more and more items were purchased from equipment vendors.

As an example of this, the Otis factory in Hamilton, Canada could produce virtually every part of every type of elevator. This factory was originally, in the early part of the 20th century, owned by the Fensom elevator company - a Canadian company. This company was merged with Otis to create Otis-Fensom and then later just Otis. The Hamilton factory was closed in the eighties as part of a program of rationalization of production.

In recent years the elevator companies, rather than manufacturing, have been purchasing much of their equipment. This has led to the development of companies that market their products almost exclusively to the industry rather than directly to the final user.

One of the long established companies in this area is GAL of New York. They make door operators and door equipment which is generally considered to be the standard in the industry. ECI, a Canadian company competes directly with them in this field. Both companies seem to do quite well. In addition, GAL has a sister company Hollister-Whitney which manufactures geared machines and a good economical rope brake.

The German company Ziehl-Abegg has been supplying elevator motors for some years as has the French company Leroy-Somer.

In fixtures, the Canadian company Dupar has a good line of devices. Their US89 line of pushbuttons has gained wide acceptance with architects based on appearance and in the industry based on performance.

All of these products compete with and in some cases replace various "in-house" products offered by the elevator manufacturers. The net result is that the end user has a wider choice of good products.

In North America we have one elevator for every two hundred people. On the other hand we have one doctor for every four hundred people.

Although these figures are approximate it is clear that we have more elevators than doctors to serve a given number of people.

It has been suggested that everyone would be healthier if we walked up one floor and down two floors rather than take the elevator.

If this were done, the number of elevators would then drop. However, since we would be healthier the number of doctors would also drop.

Perhaps the two-to-one ratio of elevators to doctors is a constant in an advanced society? And is the answer to lower health costs the removal of elevators?

In the past few years there have been several accidents involving hydraulic elevators in which the elevator has dropped abruptly, crashing into the pit and killing or injuring the passengers.

The cause is the failure of the hydraulic cylinder. This failure results from the fact that it is placed beneath the elevator and buried in the soil. Electrolytic action causes the steel cylinder to corrode and burst. When this happens the column of oil supporting the elevator is expelled into the surrounding earth and the elevator drops - in more or less free-fall.

Catastrophic failure of the buried cylinder has been, in all of the accidents to date, related to the failure of the bulkhead at the bottom of the cylinder. This bulkhead is a circular steel plate - a sort of plug - which is welded inside the cylinder to make it water (or in this case oil) tight. The electrolytic action seems to attack this weld in preference to the other parts of the cylinder. When the weld has been eaten away the bulkhead "pops" out - something like a champagne cork.

The first major accident of this type occurred in the late sixties. In the late seventies the various safety codes were revised to require a double bulkhead. This design has the same bulkhead as before but in addition a second bulkhead placed slightly higher up in the cylinder. In this second bulkhead a small hole is drilled so that if the first bulkhead fails the elevator will move down very slowly. This preserves the safety of the installation and at the same time gives a warning that something is wrong.

This design seems to deal with the safety problem. The side of the cylinder will still be attacked by corrosion but for whatever reasons there has been no example of a catastrophic side wall failure. The typical failure is characterized by pin holes in the steel wall with consequent slow loss of oil. There is therefore enough warning of trouble and potential hazard to allow corrective action to be taken.

More recently, the codes have required that buried cylinders be installed within plastic pipes so as to ensure that the cylinder will not rust.

Given the difficulties attendant upon the use of buried cylinders the trend today is towards hydraulic designs with exposed cylinders. In particular, the "holeless" hydraulic and the "roped" hydraulic are becoming more popular. These designs avoid the problem altogether since there is no buried cylinder.

As the world gets squeezed more and more for space with more and more people populating our planet there is an increasing tendency towards higher buildings in some of the more densely populated urban areas of the world.

This tendency is also fueled, apart from practical considerations of space, by the desire to have the "tallest building in the world" or at least if not the tallest, one of the tallest. To some extent the prestige of a city or its degree of modernity is measured by the height of its buildings.

As part of this "higher-high-rise" trend, a few elevator companies - notably in Japan - have begun experimenting with faster elevators. Consideration is being given to elevators traveling at speeds of 1000 and 2000 meters per minute.

Unfortunately, as elevators travel faster, the air pressure changes faster. The experience is similar to flying in an unpressurized airplane. The change of pressure with change in altitude can be quite uncomfortable because of the problems it causes to the inner ear.

Each person reacts differently to the pressure change; it is a purely individual and subjective phenomenon. There is no absolute criterion that will fit all people.

When the PanAm building was constructed in New York City after the Second World War, Westinghouse, the elevator contractor designed the high rise group to travel at 1800 fpm (550 meters per minute). It was reported that the elevator passengers found the pressure change sufficiently uncomfortable that their complaints led to a reduction of the speed to 1600 fpm (490 meters per minute). If this is to be believed then this could be considered the upper limit of acceptable elevator speed.

On the other hand it was also rumoured that the speed was reduced because there were problems with the speed control system. Take your pick.

In any case, there is a limit.

Japanese researchers have published information indicating that their tests show that much higher speeds (and consequently much higher pressure changes) can be tolerated. These tests were made with volunteers (at least we assume they were volunteers) in pressure chambers. The terminology used is of course significant. A test subject may accept pressure changes that the average high rise office occupant would not. One could expect more reluctance to experience discomfort from someone paying top prices for luxury office space.

Perhaps the answer is indeed that if we wish to keep one hundred percent of the building population happy, we will have to either accept the 490 to 500 meter per minute speed limit or find means to channel passengers through space locks and pressure chambers so as to maintain acceptable pressure change.