CHAPTER VI.Hose.

The more important steps in the evolution of the modern vacuum cleaning system can each be attributed to a change in the design or construction of some one of its component parts, which, in their former standard design, have acted as a limiting factor governing the form and size of other and more important parts of the system.

That part of the early systems which played the most important role as a limiting factor was one for whose production the builder of the system had to look to other manufacturers: namely, the flexible hose connecting the renovator stem to the rigid pipe lines and vacuum producer.

The early builders of vacuum cleaning systems naturally adopted a standard article for use as a flexible conduit; that is, the vacuum hose which had been used as suction lines for pumps of various characters. For such use it was not necessary that the hose be moved about to any great extent and, therefore, its weight was not an important factor and had been sacrificed to strength to withstand collapse and the rough handling to which suction hose is subject.

This standard hose was built up of many layers of canvas wound around a rubber tube or lining. A spiral wire was imbedded between the layers of canvas to prevent collapse and the whole was provided with an outer covering of rubber. Generally five to seven layers of canvas were used and the resulting hose was not highly flexible.

When used as a flexible conduit in connection with a vacuum cleaning system it became necessary to constantly move the hose back and forth and around the room to be cleaned. It was also necessary to limit the weight of the hose to that which could be easily handled by one person. This led to the adoption of small sizes of the then standard hose, ³⁄₄-in. diameter being first used, but soon this was abandoned in favor of 1-in. diameter hose weighing nearly 1 lb. per foot of length, which is the maximum weight that can be conveniently handled byone person. This size hose has become the standard for all systems maintaining a vacuum at the separators of 10 in. of mercury or more.

Owing to its lack of flexibility this type of hose is easily kinked and is damaged by the pulling out of such kinks, causing the tubing or lining to become separated from the canvas and to collapse, rendering the hose useless. There is also considerable wear at the point of connection to the stems of renovators, where rigid connections are used.

The outside of this hose, being rubber, is always liberally covered with soap-stone when it leaves the manufacturer, and when new hose is dragged about over carpets, it frequently soils same to a greater degree than they are cleaned by the renovator. When this hose has been in use about twice as long as is necessary to wear off the soap-stone, its appearance becomes far from handsome and is not considered to be in keeping with the nickel-plated appliances which are furnished with the cleaning tools. To overcome this objection, an outer braid has been applied generally over the rubber coating, thus adding further to its already great weight.

What was perhaps the first type of hose to be produced especially for use with vacuum cleaning systems was that in which the fabric was woven in layers, instead of being wrapped spirally around the central tube or lining. Steam was introduced into the lining, vulcanizing the lining and firmly uniting the whole mass. This hose was made 1 in. in diameter, without any metal re-inforcement, and was covered with the usual rubber coating and with braid, when ordered. This hose weighed 12 oz. per lineal foot and 1-in. diameter was still the largest that could be easily handled.

The first attempt to produce a light-weight hose for use with vacuum cleaning systems was by covering a spiral steel tape with canvas. The air leakage through this hose was found to be so high that its use resulted in loss of efficiency of the cleaning plant and it was found necessary to line the hose with rubber. This rubber-lined hose is made in larger sizes than formerly used and 2-in. diameter hose weighs approximately 14 oz. per lineal foot. It is also much more flexible than the 1-in. hose formerly used.

The introduction of this type made it possible to use largerhose in connection with vacuum cleaning systems and permitted the use of a lower vacuum at the separators, with the same results at the carpet renovator, and a larger quantity of air when using the brushes and other renovators. Without this type of hose the low-vacuum, large-volume systems would be impractical.

Another type of hose has been recently introduced in which a wire is woven into the fabric of the hose and the rubber lining vulcanized into place as already described. No outer coating of rubber is used and, therefore, no braid is necessary. This gives a light-weight hose of great flexibility and neat appearance and is undoubtedly the best hose for residence work. It is more costly than the steel tape hose which is recommended for office building and factory use, where appearance is not important.

FIG. 46. BAYONET TYPE OF HOSE COUPLING, INTRODUCED BY THE AMERICAN AIR CLEANING COMPANY.

—The earlier systems used couplings having screw-threaded ground joints, similar to those which were then in use on hose intended to withstand pressure. These couplings require considerable time to connect and disconnect and the threads are easily damaged by dragging the hose about. The exposed metal parts of the couplings are liable to scratch furniture.

To overcome the time required to connect and disconnect the screw-coupling, the American Air Cleaning Company introduced the bayonet type of coupling, as illustrated inFig. 46. This coupling is not readily damaged by rough handling, but it has metal surfaces exposed which will scratch furniture.

Both of these couplings have the disadvantage that the air current in the hose must always be in the same direction and the same end of the hose must always be next to the renovator handle. Both of these features tend to increase the wear on the hose, and the reversal of the air current to remove stoppages is not possible.

The coupling produced by the Sanitary Devices Manufacturing Company has a piece of steel tubing fitted into each end of the hose and secured by means of a brass slip-coupler fitting over the tubing. All ends being alike, the reversal of the hose is possible with this form of coupling. However, the metal coupler is liable to mar furniture and sometimes there is trouble with the couplings pulling apart.

FIG. 47. ALL RUBBER HOSE COUPLING USED BY THE SPENCER TURBINE CLEANER COMPANY.

Much of the hose in use today is provided with “pure gum” ends are vulcanized in place, it is necessary to take the hose of metal tubing is slipped inside of these ends to make a coupling. With this arrangement there is no metal exposed to mar furniture and the hose lengths are reversible. However, there is some trouble from the couplings pulling apart. Since these ends are vulcanized in place, it is necessary to take the hose to a rubber repair shop whenever the hose breaks back of the coupling, which occurs frequently when rigidly attached to thestem of the renovator. These repair shops are much more numerous than a few years ago and this drawback is not a serious one.

Another form of coupling used by the Spencer Turbine Cleaner Company is the all-rubber male and female end, as illustrated inFig. 47. This has the advantage over the metal-slip couplings and the coupling with pure gum ends in that when it is properly locked it cannot be pulled apart. It is absolutely air tight, which is true of no other coupling. But it does not permit the reversal of the hose and is, therefore, recommended for use only with hose of 1¹⁄₄-in. diameter or larger, where there is less liability of stoppage, and where the ball-bearing swivel is used at the connection to the stem, preventing excessive wear at this point. The pure gum ends, with the internal-slip coupler, is considered to be the most satisfactory for use in all cases, except as above stated.

—Hose friction plays an important part in the action of any vacuum cleaning system. In fact, where 1-in. hose is used, it becomes a limiting factor in the capacity of the system to perform some kinds of cleaning.

There are several tables of hose friction published by the manufacturers of vacuum cleaning systems, all of which appear to have been based on a constant velocity within the hose equal to that which would be obtained if the air were at atmospheric pressure throughout the entire length of the hose. But in practice the air is admitted to the hose from the renovator at a considerably lower absolute pressure of from 25 in. to 27 in. of mercury, and is, therefore, moving at a higher velocity. As the pressure is decreased by the friction loss in the hose, the velocity constantly increases with the expansion of the air.

The results of many tests made by the author during the past seven years, with hose ranging from 1-in. to 2-in. diameter and with an entering vacuum ranging from 0 to 7 in. of mercury and a friction loss of from 1 in. to 25 in. of mercury, indicate a close agreement with the formula given in Prof. William Kent’s “Mechanical Engineer’s Pocketbook,” which is based on the formula:

Q = c√pd⁵wL

Q = free air in cubic feet per minute.

c = a constant which was determined by D’Arcy as approximately 60.

p = the loss of pressure in pounds per square inch.

d = the diameter of pipe in inches.

L = the length of pipe in feet.

w = the density of the entering air in pounds per cubic foot.

Reducing the pressure loss to inches of mercury and using in lieu of w, r which is the ratio of the average absolute pressure in the pipe to atmospheric pressure, this formula becomes:

Q = 310.3√pd⁵Lr

To permit the rapid calculation of the air quantity which can be passed through a hose, the author has prepared the diagram shown inFig. 48. To use this table, look up the friction loss in the hose in the right hand margin, pass along the horizontal line to the left until it intersects the line inclined at an angle of 45° toward the left, indicating the length of the hose. From this intersection pass vertically to the line inclined at approximately 30° toward the left, representing the diameter of the hose. The quantity in the left-hand margin, opposite the horizontal passing through this intersection, represents the quantity of air which would pass through this hose in cubic feet at the average density in the hose. To correct this quantity to free air, step off the distance on the vertical line from the bottom of the table, representing the average degree of vacuum in the hose, to its intersection with the curved line near the bottom of table. Transfer this distance vertically downward on the left hand margin from the quantity first read on this margin. The quantity opposite the lower end of this distance will be the cubic feet of free air per minute passing through the hose under these conditions.

The line inclined towards the right, which passes through the intersection of lines representing hose diameter, and the horizontal line representing the cubic feet of air passing through the hose at actual density in same, shows the actual velocity in the hose in feet per second.

For friction loss over 10 in. of mercury, use the figures at the right hand of the lower margin, instead of those in the right hand margin, and pass vertically to the hose diameter.Then proceed as before. As these high frictions are seldom used in practice, this departure has been made in order to reduce the size of the diagram.

FIG. 48. CHART FOR DETERMINING HOSE FRICTION.

To illustrate how much the friction tables, based on air at atmospheric density, vary from actual results, two tests made by the author are given. In the first test it was desired to pass 68 cu. ft. of free air per minute through a ⁷⁄₈-in. diameter orifice at the end of 100 ft. of 1-in. diameter hose. Tests on larger hose showed that, to permit this quantity of air to pass through the orifice, a vacuum at the orifice of 2.6 in. mercury was necessary. The most rational table the writer could find indicated that the friction loss in the hose should be 18 in. mercury, and the final vacuum necessary at the hose cock would have to be 20.6 in. mercury. On test it was found that, with 24.8 in. vacuum at the hose cock, but 50 cu. ft. of free air per minute was passing, with a vacuum at the orifice of 1.6 in. mercury, showing a friction loss of 23.2 in. mercury. With the smaller quantity of air passing, the same friction table indicated a friction loss, with this quantity of air, of but 9.8 in. mercury, or 39% of that actually observed. Checking the results of the test with the diagram (Fig. 48) gives 50 cu. ft. of free air, with a friction loss of 23 in. mercury.

To illustrate more clearly the effect of the increase of velocity on the friction loss, the actual vacuum in the hose has been computed for each 10 ft. of its length and curves drawn through these points. The results are shown inFig. 49. The straight line indicates the vacuum which should exist were the velocity in the hose constant throughout its length, and the curved line shows the vacuum in the hose when the effect of the increasing velocity, due to the rarefaction of the air, is considered. The wide variation in the results shows clearly the error in the former assumption of a constant velocity in the hose throughout its length.

Another test, in which 44 cu. ft. of free air was passed through 100 ft. of 1-in. diameter hose, is shown graphically inFig. 50, which discloses that the assumption of a constant velocity in the hose produces an error of 35% in the results, indicating a loss of but 7.8 in., when the actual loss is 12 in. mercury.

Naturally, the lower the final vacuum at the hose cock, the less will be the error due to the assumption of constant velocity in the hose. Tests with 1¹⁄₂-in. hose gave results which agreesubstantially with the result given in tables already published, and it was this condition that led to the discovery of the error in the assumption stated.

FIG. 49. EFFECT OF INCREASE OF VELOCITY ON THE FRICTION LOSS.

—As any increase in the degree of vacuum necessary to be maintained at the vacuum producer over that maintained within the renovator requires a greater expenditure of power, without any increase in the efficiency or speed of cleaning, it is essential that the friction loss in the air conduit from the renovator to the vacuum producer should be made as small as possible. The friction loss in the hose is the greatest loss in any part of the system, being the smallest in diameter, and its reduction to the lowest figure possible is of vital importance.

Take, for example, the use of a Type A renovator with a vacuum within the renovator of 4¹⁄₂ in. mercury and with 29 cu. ft. of air passing through same. The friction loss, with varying lengths of different-sized hose, will be as follows:

TABLE 6.Vacuum at Hose Cock with Type A Renovatorsand with Varying Lengths of Different-Sized Hose.

FIG. 50. ANOTHER TEST SHOWING FRICTION LOSS DUE TO VELOCITY.

This indicates, first, that a much lower friction loss will result with the use of larger hose than is the case with the smaller size. Note, also, that the difference in the final vacuum at the hose cock is much more uniform when the larger-sized hose is used in varying lengths. Since it is desired to maintain a constant vacuum at the renovator at all times and it is also desirable to be able to vary the length of hose to suit the conditions of the work, while it is not convenient to vary the vacuum at the hose cock, much more uniform results will be possible when larger hose is used. If the smaller hose is used in varying lengths and a practically uniform vacuum is maintained at the hose cock, the quantity of air and the vacuum at the renovator will vary. If 1-in. hose is used and the vacuum at the hose cock be maintained at 10 in. mercury, the air quantities and vacuum at the renovator will be approximately:

TABLE 7.Air Quantities and Vacuum at Renovator with 1-in. Hoseand 10-in. Vacuum at Hose Cock.

From this it is evident that the vacuum within the renovator will be increased above that necessary for economical cleaning. It will require somewhat more effort to push the cleaner over the carpet and also a slightly greater expenditure of power at the hose cock to operate the cleaner with a short than with a long hose. However, the author does not consider that either the increase of effort to push the renovator or the increase of power will be sufficient to prohibit the use of 1-in. hose with the Type A renovator.

If we use 1¹⁄₄-in. hose with Type A renovator and maintain a vacuum of 6 in. of mercury at the hose cock, the resulting vacuum and air displacement at the renovator will be:

TABLE 8.Air Quantities and Vacuum at Renovator with 1¹⁄₄-in. Hoseand 6-in. Vacuum at Hose Cock.

This table shows a more uniform degree of vacuum at the renovator with the varying length of hose, but the greatest difference is in the horse power required at the hose cock to accomplish the same results at the renovator.

If we use 1¹⁄₂-in. hose with Type A renovator, the vacuum at the hose cock can be reduced to 5 in. mercury and a practically constant vacuum will be obtained at the renovator, with an expenditure of 0.36 H. P. at the hose cock.

With the Type C renovator where the vacuum within the renovator is maintained at 4 in. mercury, with 44 cu. ft. of free air per minute passing through the renovator, the resulting vacuum at the hose cock, with various lengths of the three sizes of hose, will be as follows:

TABLE 9.Vacuum at Hose Cock, with Type C Renovatorsand Various Lengths of Three Sizes of Hose.

Referring toFig. 17, Chapter III, it will be noted that Type C renovator will not accomplish much in the way of cleaning with a vacuum in the renovator lower than 4 in. mercury. Therefore, if we use this type of renovator, with 1-in. diameter hose, its length should be limited to 50 ft., for if we use a vacuum higher than 10 in. at the hose cock, there will be too much increase in the vacuum at the renovator when short hose is used to allow easy operation, and if we use longer hose with 10-in. vacuum at the hose cock, there will be a reduction in the vacuum at the renovator and effective cleaning cannot be accomplished. Also, the power required at the hose cock to pass 44 cu. ft. of air, with a vacuum of 19 in. mercury, required to produce a vacuum of 4 in. at the renovator with 100 ft. of 1-in. hose, will be 3.3 H. P., which is prohibitive when compared with that required with the use of larger hose, i. e., 0.825 H. P. with 1¹⁄₄-in. hose and 0.59 H. P. with 1¹⁄₂-in. hose.

The Type F renovators tested by the author will show even wider variations in the vacuum required at the hose cock with the various lengths and diameters of hose than is given for Type C renovator. However, the type F renovator, which is now used by the Spencer Turbine Cleaner Company, having a cleaning slot 15 in. long and ¹⁄₂ in. wide throughout its length.passes 44 cu. ft. of free air per minute, with a vacuum under the renovator of 4 in. mercury and the resulting vacuum at the hose cock will be the same as that given in the case of the Type C renovator.

When a bare floor renovator of the bristle-brush type is attached to the hose, the effect is practically the same as when the end of the hose is left wide open, as the open character of the brush prevents the formation of any vacuum in the renovator. Therefore, sufficient air must pass through the renovator to create a friction loss in the hose equal to the vacuum at the hose cock.

As practically all systems are arranged to maintain a constant vacuum at the vacuum producer and as the pipe friction is generally less than the hose friction, the vacuum at the hose cock will be practically the same when operating a floor brush as with a carpet renovator.

Assuming that 10 in. mercury is maintained at the hose cock with 1-in hose, 6 in. with 1¹⁄₄-in. hose, and 5 in. with 1¹⁄₂-in. hose, the quantity of air which will pass through a floor brush with various sizes and lengths of hose will be:

TABLE 10.Air Quantities Through Floor Brush Operated inConjunction with Type A Renovators.

The quantities given for the shorter hose lengths are higher than will be observed in actual practice, due to the increase in the pipe friction, which will depend on the length of the pipe lines. However, the results will illustrate the great increase in the quantity of air which will pass these bare floor brushes when operated on the same system with carpet renovators. If the same number of bare floor renovators are to be used at one time as there will be carpet renovators at some other time,that is, if the sweeper capacity must be maintained when using bare floor brushes as when using carpet renovators, a much larger air exhausting plant must be installed than would be necessary to operate that number of carpet renovators.

If it were possible to so arrange the schedule of cleaning operations that bare floor brushes were never used at the same time as carpet renovators, the vacuum at the machine might be reduced when operating the floor brushes to a point that would reduce the quantity of air passing to within the capacity of a machine designed to operate the same number of carpet renovators. Unfortunately, this condition rarely exists and, therefore, the vacuum must be maintained at the degree necessary to operate the carpet renovators that may be in use at the same time with the floor brushes.

It is also evident that if the length of hose used with bare floor brushes could be limited to the maximum ever used with the carpet renovators, a reduction in the capacity of the exhauster necessary could be made. This is another condition which the designer of the system cannot control.

—The horse power required at the hose cock to operate the bare floor brushes with each of the different sizes and lengths of hose is:

TABLE 11.Horse Power Required at Hose Cock to OperateBare Floor Brushes in Conjunction with Type A Renovators.

This shows that where bare floor or wall brushes of the bristle type are used in conjunction with carpet renovators on any system and with Type A carpet renovator, 1¹⁄₄-in. diameter hose will give the lowest power consumption.

When either Type C or F renovator is used in combination with bristle-type brushes, the use of 1-in. diameter hose must be abandoned in lengths over 50 ft. and the vacuum at the hose cock must be maintained at 10 in. mercury. With 1¹⁄₄-in. hose, it will be necessary to maintain a vacuum at the hose cock of 7 in. mercury, and, with 1¹⁄₂-in. hose, 5 in. will be sufficient, provided we continue to use 100 ft. of hose in the case of the larger sizes. The free air passing a brush type of bare floor renovator under these conditions will be:

TABLE 12.Free Air Passing Brush Type of Bare Floor RenovatorOperated in Conjunction with Type C Renovators.

This shows an increase in the volume of air passing the floor brush with 1¹⁄₄-in. hose, while a higher vacuum is now carried at the hose cock than was necessary when Type A renovator was used in conjunction with the bristle-type of floor renovator. The horse power at the hose cock will now be:

TABLE 13.Horse Power at Hose Cock with Brush Type ofBare Floor Renovator Operated in Conjunctionwith Type C Renovators.

With this combination of floor and carpet renovators, there is no difference in the power consumption when any one of the three sizes of hose is used. However, there is a considerableincrease in the quantity of air passing the larger hose. This leads to the statement made by some manufacturers that this increase in air volume results in more efficient cleaning.

Tests given inChapter IIIindicate that increase in air volume does not result in any more rapid or efficient cleaning of carpets. The results of actual use of the bare floor brush of the bristle type show no gain when cleaning bare floors. As stated inChapter IV, the felt-faced renovator, being more effective while it requires less air. In other words, it is the degree of vacuum within the cleaner and not the quantity of air which produces the cleaning in all cases where any degree of vacuum is possible. When intimate contact between the cleaner and the surface cleaned cannot be had, the volume of air determines the efficiency of cleaning. However, the author does not consider that an exhaustion of more than 60 to 70 cu. ft. of free air through cleaners of this type will increase the efficiency to such an extent as to justify the increase of power necessary to adapt a system to larger volumes.

The author considers that with a system in which brushes of the bristle type are to be used, the exhauster should have a capacity of 70 cu. ft. of free air per minute. Such a system is termed by the author a “large volume system,” as already mentioned inChapter IV.

When the felt-covered floor renovator is used instead of the brush, the vacuum within this renovator must not be permitted to rise above 2 in. or the operation of the renovator on the floor will be difficult. To accomplish this, it is necessary to provide openings in the ends of the cleaning slot, as has been explained inChapter IV. If the vacuum at the hose cock be assumed as 10 in. with 1-in hose, 6 in. with 1¹⁄₄-in. hose, and 5 in. with 1¹⁄₂-in. hose, and the vacuum within the felt-covered floor renovator be maintained at 2 in. mercury the cubic feet of free air passing the renovator with the various sizes and lengths of hose will be:

TABLE 14.Cubic Feet of Free Air Passing the Felt-CoveredFloor Renovators Operated in Conjunction withType A Renovators.

These figures show a considerable reduction from those obtained with the brush type of floor renovator, particularly when the larger sizes of hose are used, and considerable reduction can be made in the capacity of the exhauster and still obtain the best results when using carpet renovator and bare floor renovator simultaneously.

The horse power at the hose cock required to operate these felt-faced floor renovators with different sizes and lengths of hose are:

TABLE 15.Horse Power Required at Hose Cock to OperateFelt-Covered Floor Renovators in Conjunctionwith Type A Renovators.

In this case, the 1¹⁄₄-in. hose is the most economical size to use, as was the case with the brush renovators. However, the advantage over the 1¹⁄₂-in. hose is not as great as with the brush renovator.

With this type of renovator, the manufacturer has some control over the length of hose which the operator will use in connection with the bare floor renovator, as he may open the ends of the renovator just sufficiently to produce 2 in. of vacuum under same with, say, 50 ft. of hose. Then, if theoperator should attempt to use the renovator with 25 ft. of hose, it will stick and push hard and he will soon learn that a longer hose is necessary.

—For locations where it is desirable to sacrifice efficiency somewhat to reduction in the amount of power required, as in residences, the Type A carpet renovator may be used and the vacuum under the same reduced to 2 in. mercury, which will still do effective cleaning, but at a slower rate, as was shown by tests inChapter III. This requires not exceeding 20 cu. ft. of free air per minute.

With this quantity of air the velocity in the hose must be considered as, in order to have a clean hose at all times, it is necessary to maintain a velocity in the hose of not less than 40 ft. per second. Referring to the diagram,Fig. 48, it will be seen that this velocity will not be obtained in any hose larger than 1¹⁄₄ in. and this is, therefore, the largest size which can be used. In all the former cases the velocity was so much in excess of this minimum that its consideration was not necessary.

With a vacuum of 2 in. of mercury in the renovator and 20 cu. ft. of air passing, the vacuum at the hose cock will be:

TABLE 16.Vacuum at Hose Cock, with 2-in. Vacuumat Type A Renovator.

In this case the increase in vacuum at the renovator would not be objectionable as, with 4 in. vacuum at the hose cock, the vacuum at the renovator would never reach the standard used with the former deductions and the volume of air passing could, therefore, never reach 29 cu. ft. Any increase, due to the use of shorter hose, would, therefore, be an advantage in its approach toward the standard set for the larger plants. Therefore, we will assume that a vacuum of 4 in. mercury will bemaintained at the hose cock with 1-in. hose and a vacuum of 2¹⁄₂ in. at the hose cock with 1¹⁄₄-in. hose.

The renovators for bare floor work will be the felt-covered type and will be opened at the ends just sufficiently to limit the vacuum within the same to 2 in. mercury when operating with 25 ft. of hose. This will require the passage of 40 cu. ft. of free air per minute when 1-in. hose is used and 35 cu. ft. when 1¹⁄₄-in. hose is used. The horse power at the hose cock will be 0.39 H. P. with the 1-in. diameter hose and 0.17 H. P. with the 1¹⁄₄-in. hose. Here again we see that the 1¹⁄₄-in. hose is the more economical to use.

If bristle brushes are used with this system at the same time that carpet renovators are in use, the quantity of air which will have to pass them, in order to maintain the vacuum on the system at the proper point to do effective cleaning with the carpet renovators, will be:

TABLE 17.Air Quantities When Bristle Bare Floor RenovatorsAre Used in Conjunction with Type ACarpet Renovators at 2 in. Hg.

The use of these brushes in plants of more than one-sweeper capacity would require the use of an exhauster of greater capacity than is required for either the carpet or the bare floor renovator. Where the plant is of but one-sweeper capacity, the quantity of air that would pass these brushes, were the plant of proper capacity to serve the carpet and floor renovators, would not be sufficient to do effective work, as was explained inChapter IV. In such cases, this arrangement should be prohibited.

A system of the type just described is what has been termed by the author as a “small volume” plant inChapter IV.

—The author has made the deductions in this chapter, using 100 ft. of hose as the maximum length. This is considered to be the greatest length that should be used. The adoption of a shorter length is recommended by many manufacturers, but the author does not consider that the advantage to be obtained by the adoption of a shorter length justifies the additional expense of piping which will result in many cases. This will be governed by the character of the building and, in many cases, it will be possible to use 50 ft. as a maximum. It has been the practice of the author to lay out his installations so that any point on the floor of any room may be reached in the most direct line with 75 ft. of hose. When this is done 100 ft. of hose will easily clean any part of the walls or ceilings and give an ample allowance for running around furniture or other obstructions.

The figures in this chapter will demonstrate to the reader the part that the cleaning hose plays as a limiting factor in the operation of a vacuum cleaning system and shows the care that must be exercised in the selection of the proper hose for each condition.

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