For the successful operation of high buildings the elevator forms an integral part of the building. The physical deterioration of this part of the equipment is compound, consisting of that due to the fixed portion of the construction, the hoistway - guides and beams - and that of the motive portion or engine with accompanying apparatus, such as valves, gears, wheels, bearings, drums, shafts, ropes, and motors.

An adequate number of such appliances, providing not only an ample but an easily operated service, will have a longer physical life than one in which, by a shortage of machines, the service becomes severe, involving heavy loads, frequent reversals, and general wear and tear. The elevator, like any other moving apparatus, requires constant care and minute supervision to maintain it in thorough serviceable order. If all the elevators in a building are in constant urgent use, there is not available time for this work of upkeep to be properly effected.

Table G. Economic Existence Of Mechanical Apparatus

I. FIXED EQUIPMENT

Life in years

Steel construction, foundations, elevator guides, and overhead framing ......................

30

Exterior framing, copper-cased housings, heating pipe systems used part of the year, gas piping..............

27

Buried vents and ducts when painted...........

26

Steel-plate stacks and smoke-ducts, cold-water piping, electric conduits

24

Heating-boilers used part of year

22

Roof-tanks, sanitary piping systems

21

Pressure steam piping and appliances, interior drums and tanks, hot-water and pneumatic piping.............

20

Exposed and unpainted vents and ducts

19

Highest-class pressure steam-boilers

17

Sanitary fixtures, refrigerating piping, kitchen fixtures, and valves .

16

Drip and drain piping, cheaper class of pressure steam-boilers . . .

14

Electric switches, wiring, and connections....... , . .

II

Exhaust heads, exposed galvanized ironwork, hot-water drums . .

9

II. Motive Appliances

Slowest-speed apparatus, apparatus intermittently used.....

20

Dumb-waiters, switchboards, elevator gates, slow-speed elevator engines, shafting and bearings, slow-geared apparatus, elevators intermittently used

18

Motor-driven pumps, compressors, and moderate-speed fans . . .

17

Slow-speed reciprocating apparatus, such as pumps, elevator reversing gear, platform lifts

15

Elevators in regular use, laundry, kitchen, refrigerating, electric devices, and other apparatus frequently reversed.......

14

Moderate-speed reciprocating engines, medium-speed rotary apparatus, dynamos and motors..............

12

Fan engines, high-speed rotary apparatus on large variations of loads, dynamos, motors, high-pressure engines, condensers.....

9

High-speed, high-pressure, reciprocating engines and machines on extreme variable loads

7

The effective life of much of the appliances is thus reduced, and its upkeep is at the same time rendered burdensome as well as a source of much anxiety to those charged with its maintenance. But apart from the foregoing, the economic side of the matter requires an ample provision of elevators in a building, inasmuch as inadequate or irregular service directly affects the rentable value of the upper floors, which are totally dependent for access, in lofty structures, upon the elevators.

The economic life of the apparatus is, moreover, affected by the march of mechanical improvement, and an elevator installation maintained in excellent condition may be properly abandoned in favor of another affording greater efficiency in service and perhaps in cost of operation. It cannot be assumed that the effective life of an elevator installation is equal to that of the building it serves, and, in fact, the evidence of past experience in this line is to the effect that this part of the motive appliances must be reconstituted at least once and perhaps twice during the period of effective life of the building.

This has been the case in a number of instances. In the building in which one of the earliest forms of hydraulic elevator was installed, the apparatus was replaced, after about seventeen years of service, by others of more modern hydraulic pattern. But it is reasonable to suppose that in another equal period, should the building's existence be so prolonged, another replacement by still better appliances will take place.

The steam-driven machines in several office buildings saw service of approximately a similar length of time, so that a period of about twenty years certainly has covered the life of

II Motive Appliances 26

"Extending this existence by reconstruction may be of so expensive a nature and of so limited an effect, that replacement may be preferable"

Depreciation of Mechanical Equipments and Power Plants such apparatus in the past, and there is no reason to anticipate a greater length of economic life in the future. On the contrary, in elevator engines, as in other lines of development, modern devices nearly always take the direction of high speed, which in itself contributes to physical deterioration. An ample number of elevators, of moderate speed and moderate size of cars, is the best form of economic investment in this important part of building equipment.

A noticeable feature in connection with equipment is the increase in the demand which arises as time proceeds, and which directly affects the economic side of the investment.

The apparatus, which is originally designed or purchased for a given service or combination of services, is not, by the process of use and age, improved in its capacity to respond to this increased demand, and it therefore often happens that efficiency decreases at a ratio accelerated by these two causes.

This is an effect specially noticeable in boilers, the working value of which is decreased directly by age and accompanying reduction of allowable pressure, and indirectly by irregular usage and wear and tear, so that an increased demand for output comes upon a weakened and aged appliance incapable of efficient response. Further, when the power thus generated has been planned to operate machinery with a given economic pressure, the lowering of that pressure adversely affects the economy of the machinery.

A boiler when installed may have an allowable working pressure of 100 pounds per square inch, and the engines it supplies do their work best and most economically with that pressure. As time proceeds, the boiler itself becomes less efficient by leaky setting, by fouled and choked smoke-passages, and by scaled interior, and, to cap these deficiencies, the local inspector reduces the allowable working pressure. The engines are therefore supplied at less pressure, reducing further as time proceeds, and their product is affected in both quantity and economy, until some point is reached in the scale where the owner is compelled to undertake rebuilding or replacement.

The operation of extending this existence by remodeling, by reconstruction, or by additional apparatus may be of so expensive a nature, and of so limited an effect, that their entire reconstruction or replacement may be economically preferable.

Radical remodeling, involving more or less reconstruction, may bring the appliance up to reasonable mechanical efficiency, yet may not bring it to the point of full effectiveness to meet the growth of demands for its work. Therefore the conservative practice will be to set aside an annual percentage of value which will cover complete replacement within the period of effective earning existence, so that provision may.be made in advance for such contingencies as have been referred to, which percentage can be readily ascertained by reference of any item to the corresponding rate of compound interest in Table E.

As regards the life of usefulness of power-generating machinery, the further consideration must be applied that the commercial value of such apparatus ends as soon as the cost of its operation reaches the price at which its output could be purchased from another source of supply or supplied by some other substitute.

Lenders of money upon security of improved real estate sometimes demand the installation of machinery therein, regarding it as a part of their security; but the value of motive machinery in such a connection is discounted by its relatively short period of useful existence and by the probability of necessary replacement more than once during the life of the structure. Moreover, the mortgageable value of such apparatus, even if regarded as part of the building, is but second-hand value as soon as it is put in operation.

If a mortgage or bond is secured in part upon motive appliances, that part of the security declines at a much more rapid rate than the building, and would seem to require the establishment of a special and regularly invested sinking-fund in order to maintain its stability, since the relative life of motive appliances as compared with that of the building is only from 20 to 27%.