When operated with Type A carpet renovators, these curved stems were apparently satisfactory. However, when they were used in department stores, and other places where much bare floor cleaning was necessary, the stems were cut through at the curved portion by the sand blast action of the dust. The cutting of these stems in bare floor work, while they were satisfactory in carpet cleaning, indicates that the velocity in the stem, due to the large volume of air passing the bare floor renovator, was too great for this soft metal to withstand the impact of the dust on the curved surface. With the systems in use at that time no means were provided to control the vacuum at the vacuum producer and the hose and pipe lines were small, both of which tended to cause a wide variation in the volume of air exhausted under various conditions, in the character of surface cleaned, and in the number of renovators in use. Therefore, the value of this destructive velocity is not readily obtainable. However, the author considers that, in extreme cases, the quantity of air passing through these stems may have been as high as 55 cu. ft. per minute. As the inside diameter of the stems was ³⁄₄ in. the area was 0.44 sq. in., or 0.00328 sq. ft., and the velocity through the stem was nearly 17,000 ft. per minute. With an average air passage of 40 cu. ft. per minute the velocity was 12,200 ft. per minute.
Referring to tests of carpet renovators, [Chapter III], it will be noted that the maximum volume of air passing through carpet renovators of Type A was 33 cu. ft. per minute, which gives a velocity of 10,000 ft. per minute. Apparently, at this velocity, the cutting action, due to the impact of the dust on the curved surfaces, was not severe. However, the author considers that the maximum velocity that should be permitted through these stems is 9,000 ft. per minute.
As the dirt picked up must be lifted almost vertically, the velocity in the stem must not become too low or dirt will lodge in the stem. Experiments made by the author indicate that the minimum velocity should be at least 4,000 ft. per minute, in order to insure a clean stem at all times.
Shortly after the introduction of vacuum cleaning, the use of drawn-steel tubing for the manufacture of stems for cleaning tools was standard with one manufacturer and, lately, its use has become almost universal, except in cases where very long stems are necessary, as on wall brushes when cleaning very high ceilings. For such work, aluminum stems have been adopted.
This harder metal will better withstand the cutting action of the dust and can also be made much thinner and lighter in weight than brass tubing of equal strength. These stems were made from 1 in. outside diameter, No. 21 gauge tubing, having an internal area of 0.68 sq. in., and the author does not know of any cases where these stems have been cut by the impact of the dust.
Stems of this metal are recommended by the author for use with all floor renovators and with wall brushes, except in cases where exceedingly long stems are required, when those of drawn aluminum tubing are recommended.
For use with Type A renovators, where the minimum air quantity is approximately 22 cu. ft. per minute, the greatest area permissible is 224000 = 0.0055 sq. ft., or 0.79 sq. in., equivalent to 1-in. diameter. With a maximum air quantity, under proper control, of 39 cu. ft. per minute, the minimum area will be 399000 = 0.00433 sq. ft. or 0.625 sq. in., equivalent to 0.89 in. diameter, so that a 1-in. outside diameter stem of No. 21 gauge metal, having an inside diameter of 0.932 in., is recommended.
For use with a Type F renovator, with a minimum air quantity of 44 cu. ft. per minute, the maximum area of the stem will be 444000 = 0.011 sq. ft., or 1.58 sq. in., equivalent to 1.4 in. diameter, while, with a maximum air quantity of 70 cu. ft. per minute, the minimum area will be 709000 = 0.0077 sq. ft., or 1.11 sq. in., equivalent to 1.18 in. diameter, and a 1¹⁄₄-in. diameter stem of No. 21 gauge metal, having an inside diameter of 1.18 in. is recommended.
Tests of Mr. S. A. Reeve, which are discussed in [Chapter III], indicate that both edges of the cleaning slot on any renovator must be in contact with the surface cleaned in order to do effective cleaning. A renovator which is rigidly connected to its stem can be effectively operated with the stem at but one angle with the surface cleaned, which makes the cleaning under furniture, or on wall at various heights above the floor, impossible. In order to do effective cleaning with any degree of speed and comfort to the operator, some form of swivel joint between the renovator and its stem is necessary.
These swivels have been made in many forms, one of which consists of two hemispheres connected by a bolt on their axis, as shown in [Fig. 37]. This form of swivel is unsuited for use under these conditions, as lint, thread and any other small articles picked up will catch on the bolt which lies directly in the path of the dust-laden air current, and its use should be prohibited in all cases.