A modification of this form of swivel has been made by the manufacturers of the last-described swivel, in which semi-circular grooves have been cut, one on the inside of the female portion and one on the outside of the male portion. Steel balls are forced into this groove, after the parts are assembled, through an opening provided in the edges of the parts. This opening is closed, after the balls are in place, by a small pin, as shown in [Fig. 43]. The swivel then becomes a ball-bearing joint, with a freedom of motion characteristic of such bearings. This joint readily responds to every movement of the stem and keeps the hose hanging vertically downward and always free from kinks. Its action is illustrated in [Fig. 44], in which it is being used in connection with a carpet renovator. This joint is considered to be the most efficient on the market. It is protected by a patent controlled by a manufacturer of vacuum cleaners.
FIG. 44. ACTION OF BALL-BEARING SWIVEL JOINT.
Valves are placed at the upper end of the stems by many manufacturers, to cut off the suction when carrying the renovators from room to room, and when it is necessary to stop sweeping to move furniture. These valves have nearly always taken the form of a plug cock with tee or knurled handle. They are useful on large installations, where vacuum control is either inherent in the exhauster or where some means of vacuum control is provided, as a considerable saving of power may be obtained by closing same, as will be explained in a later chapter, and to overcome the unpleasant hissing noise caused by the inrush of air into the renovator when same is held off the floor.
FIG. 45. ILLUSTRATION OF DEFECTS OF PLUG COCKS.
When the exhauster has a capacity of but one sweeper and when the cleaning is done at times when the building is unoccupied, there seems to be little need for this refinement, which has two defects: first, the operators will not close the valves: second, when they have been closed they are only partly opened, as indicated in [Fig. 45]. When this occurs, the portions of the plug, which are shown stippled, are quickly cut away by the sand-blast action of the dust, making it necessary to open the valve a still smaller amount the next time it is operated, cutting off still more of the plug until a new plug is necessary in order to make the valve again operative.
A few attempts have been made to overcome these defects by making the valves self-closing and having them so constructed that when the operator grasps the handle the valve will be forced wide open, on the principle of the pistol grip. These valves will, of course, close whenever the handle is released, and it is impossible to grasp the handle in any degree of comfort without throwing the valve wide open. However, since the valve is closed by a spring, considerable pressure must be applied to the handle in order to keep it open and it acts similar to the Sandow dumb bell in producing fatigue of the fingers in a short time; they have not come into general use. The use of valves in the renovator handle is considered by the author to be an expense not justified by the gain in economy and they are no longer included in specifications prepared by him.
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.