Safety Appliances for Lifts: 1895 (Part 2)

A look at the contents of Umney’s paper on lift safeties

On 10 June 1895, Herbert W. Umney (1870-1958) presented an illustrated paper on lift safeties to the Society of Engineers. Umney’s paper (titled “Safety Appliances for Elevators”), the audience’s commentary on its contents and the author’s response, were published in the Society of Engineers Transactions for the Year 1895.[1] Part one of this investigation examined the paper’s historical context and the author’s biography up to 1895. This article will explore the paper’s contents. While this exploration did not shed light on the author’s predilection for American terminology and his use of the term “elevator” over its British counterpart, it did reveal that he approached his subject in a decidedly academic manner.

Umney presented his subject in the form of an abbreviated history of British lift safeties. He began by discussing a problem associated with the recent emergence of city water systems and complex interior plumbing systems — water hammer:

“The first weak point in hydraulic lifts, which is patent to all, is the effect of any hammer action that arises when the machine is stopped or started suddenly. This shock is in no way transmitted to the mains, as consumers are always required (where the supply enters their premises) to fix a valve which shall not only act as a stop-cock, but also as a back pressure and retaining valve, in order that any failure in the power supply will not affect the machine so as to cause it to descend. This stop-valve thus concentrates any shock on the pipes within the building, and they have to bear all the sudden increase of pressure. To relieve this stress to which the pipes would be subjected, relief valves are sometimes fixed, although, the author ventures to think, not often enough.”

His suggestion that relief valves were not standard features of hydraulic lift systems speaks, perhaps, to the general absence of regulations concerning these installations.

The first safety device addressed was designed for use in the connection between the supply and discharge pipes and the hoisting cylinder. Umney stated that diaphragms “are, or should be, always placed in the joint next the cylinder, in order to regulate the speed of the lift in its ascent, and this will similarly prevent any excessive velocity of the cage when descending.” He suggested that the size of the diaphragm’s orifice or opening was best determined by a simple formula, which had been “deduced from a more elaborate one developed by Henry Adams” (Professor of Engineering at the City of London College):

In the formula, d and D represented the respective diameters of the diaphragm’s orifice and the ram in inches, v equaled the lift’s velocity in feet per second, m equaled the multiplying power, and P equaled the water pressure in pounds per square inch.

In a system that employed a balancing cylinder, the diaphragm, in order to regulate the speed of ascent, was placed in the power cylinder. However, in the event of a failure in the connection between the balancing and power cylinders, “the full weight of the ram, cage and passengers” would act to “force the water out of the (hoisting) cylinder.”[1] This deficit was addressed by the development of “ram grips.” Umney described and illustrated a grip designed by Edward B. Ellington (1845-1914) (Figure 1):

“The lift ram R is embraced by two brake blocks AA, which, by a system of toggle levers, are connected with the piston rod B of a piston C working in a small hydraulic cylinder. The back of the piston at D communicates with the pressure water, and the front at E with the lift cylinder. If the lift cylinder should burst, and the water escape from it with a velocity sufficient to reduce the pressure within it so far that the lift descended quicker than its normal speed, the excess of pressure on the back of the piston D (not connected with the lift cylinder) will cause the piston to move forward on the brake cylinder, and so make the brake clip the ram.”

The safety was also designed such that it could be “controlled by hand from the lift cage,” and, thus, could be used as a brake “for locking the lift in any desired position.”

The precise origin of the next safety device discussed by Umney is unknown; he reported that:

“Grips, however, were not considered by Sir Frederick Bramwell sufficiently reliable for the safety of passengers travelling in direct-acting hydraulic lifts fitted with water balances, so he required that a brake valve … should be made and fitted on the four lifts at St. Bartholomew’s Hospital in order to minimize any risk.”

Although Bramwell (1818-1903) was a respected civil and mechanical engineer, it is unclear whether he designed the brake valve or if he simply required its application (the identity of the lift manufacturer is unknown). The valve was placed “as near as possible to the lifting cylinder” and operated as follows (Figure 2):

“Under ordinary working conditions the pressure on either side of the valve does not vary more than 20 lb, so that a light spiral spring will easily keep the valve open. Should a pipe burst, the pressure on the upper side of the valve is relieved and the valve closes, leaving only a small hole for the water to escape through. This hole is usually about a quarter of an inch diameter, so that the sudden closing of the valve does not cause any shock, and the lift is enabled to descend gradually.”

Umney, having discussed concerns associated with “pipe failures,” now directed his “attention to gear fitted on cages so as to arrest their motion when the hauling-chain or ropes fail.”

He first described a design of “one of the earlier arrangements” of a safety “applied to a goods lift cage.” The safety was mounted on top of the car and was connected to the hoisting rope such that, if the rope broke, two sets of serrated cams would grip the T-irons that functioned as guide rails (Figure 3). Umney, however, reported that:

“Safety gear is now hardly ever fixed on the top of cages, because it is then necessary to construct a far heavier frame than would be required to carry the load, lest, under the dynamic stress resulting from the motion of the lift being arrested by the safety gear, the bottom of the cage should fall out, as it did in one instance which came directly under the author’s notice.”

Thus far, the accident referenced by Umney has not been identified. The shift in the location of safeties from the top to the sides or bottom of the car or cage paralleled events in the U.S. The first example illustrated by Umney depicted serrated wedges that gripped the sides of wooden guide rails (Figure 4).

Umney associated the next phase of safety development with the introduction of steel ropes: “With improvements in steel wire rope manufacture the lifting chain gave place to a rope and the single rope, in the case of a passenger lift, to two or four ropes. This greater number is now most common.” Following a brief discussion of steel rope characteristics and proper sheave sizes, he moved on to “the class of safety devices first adopted on the introduction of four wire ropes for raising the load.” The operation of one of the first examples of this type was described as follows (Figure 5):

“A pair of ropes is taken down on either side of the cage, and each is carried to the frame work at the bottom on opposite sides of the runners. Each rope is attached to an eye-bolt passing through a guide spindle on the frame, so that all the stress of raising the load is transferred to the bottom of the cage. These eye-bolts swivel on the spindle and pass through a guide bracket, between which a spring is compressed by a nut to such an extent that if a rope breaks and the stress on the bolt head is relieved, then the spring forces the bolt down to act on the one cam, which at the same time, by gearing, brings the others into play. There is, however, a limiting power for this spring, in order that the gear may not be brought into action whenever the empty cage descends. Such a gear, therefore, has one objection, inasmuch as its efficiency depends on the force of the spring.”

According to Umney, lift manufacturers quickly developed designs that addressed the “objection” noted above. He illustrated improved designs by Waygood, Otis and Smith & Stevens, with only the latter system’s operation fully described (Figure 6):

“The ropes AA are divided as in the spring gear, and each is fastened to the horizontal arm of one of two bell cranks BB. The other ends of the crank levers are connected together by a bar C, so that the movement of one is transmitted to the other simultaneously and the pull of the ropes is balanced. Under the cage two shafts EE pass from side to side, and at each end serrated cams FF are fixed which do not touch the runner G when the lift is travelling. The cams and coupling-bar have projecting lugs which engage one with the other, so that any movement of the cranks pushes one or other cam forward, and all four cams being coupled together by the shafts EE, the action of any one is immediately transmitted, so that each runner guide is gripped on both sides. With this gear the full weight of the cage, etc., brings the grips into action, the crank-pins carrying the entire load. If the arms of the crank-lever in this balance gear are equal, the comparative efficiency of this with the previous arrangement would be dependent on the relative rails exerted by the remaining rope R, and by the spring respectively against the friction of the cam, which may be supposed to be the same in each case.”

Umney, however, also noted that these safeties could not “be considered absolutely perfect, for a unique case has been recorded, in which all four ropes broke at absolutely the same moment.” (Unfortunately, no details were provided on this “unique” accident.) The solution was to add a fifth rope, “not to carry any load, but to bring the gear into action in the event” of an accident involving all four hoisting ropes. The most effective use of a fifth or idle rope was when it “passed over a governor, for it would then bring the safety gears into action when the speed of the lift was excessive on its downward journey, as well as act in emergency cases, when the four ropes failed.” Umney illustrated three governor designs, including one by A. & P. Steven (Glasgow) (Figure 7). However, he reported that, because “governors are without doubt costly if properly made,” they were, unfortunately, not in “great favour.”

Umney also described a safety designed by Edward William Sant (1848-1919) that employed a fifth rope that “passed over a pulley at the top of the lift,” with one end attached to the safety cam or wedge via an adjustable spring and the other end attached to “a small balance weight sufficient to keep a tension on the rope.” If the car’s descending speed exceeded “a certain rate (regulated by the spring) the inertia of the weight will cause an extension of the spring, and so bring the gear into action.” Umney claimed that he had tested this safety and that he had obtained “remarkably good results.” He also noted that he found the “theoretical consideration of the efficiency of this gear interesting, as exemplifying the simplest adaptation of the elementary principles of mechanics.” This interest led to a brief (and formula filled) aside in which he explored the relationship between the velocity of the cage and the required extension of the spring needed to activate the device. The final safety discussed was an earlier version of Sant’s design that had been developed by American inventor Albert C. Ellithorpe in 1881. In this scheme, the rope-tension-weight travelled in a tube such that “not only the inertia of the weight, but the air compressed in the tube acted together to arrest the motion of the weight and bring the gear into play.”

Umney concluded his paper by noting, “Great credit is due to manufacturers of lifts from the fact that lift accidents are so few and far between, since it is computed that not less than ninety-millions of persons are annually carried in passenger lifts in London alone.” While his estimate of the number of London’s lift passengers per year may be somewhat suspect, his enthusiastic support for the employment of lift safeties is unquestionable. The conclusion of this series will examine the audience’s reaction to and commentary on his paper and Umney’s response.

Reference

[1] Herbert W. Umney, “Safety Appliances for Elevators,” Society of Engineers Transactions for the Year 1895 (1896). Note: all quotations draw from this source.