CHAPTER XIII.Tests.
Having decided on the type of vacuum cleaning system that is best suited to the conditions of the particular building in which it is to be installed, it then becomes necessary to ascertain what are the tests necessary to determine whether the installation will produce the desired results.
If the installation is one in which carpet cleaning is important and the plant is of more than one-sweeper capacity, the exhauster must be of sufficient capacity to produce a vacuum of not less than 4 in. mercury at a carpet renovator attached to any inlet on the piping system, when the plant is operating other renovators of any type attached to any of the other inlets corresponding to one less than the total sweeper capacity of the system.
When hose lengths as short as 25 ft. can be used on any or all of the outlets, it has been demonstrated inChapter VIIthat an air removal of 70 cu. ft. of free air per minute for each sweeper of plant capacity is necessary, no matter what size of hose is used. It was also shown that where pipe lines are very long and it is possible to always use 100 ft. of hose, efficient cleaning can be done with less expenditure of power with an air displacement of 45 cu. ft. of free air for each sweeper of plant capacity.
Many methods have been recommended for testing a cleaning plant. Perhaps the earliest was the maintaining of 15 in. of vacuum at the vacuum producer with carpet renovators each attached to 100 ft. of hose, equal in number to the sweeper capacity of the plant in operation on carpets. Another test is to attach 100-ft. lengths of hose to inlets on the system, with the ends wide open, equal in number to the sweeper capacity of the plant, and require the pump to maintain a vacuum of 15 in. mercury.
Both of these tests were recommended for use on plants where 1-in. diameter hose was provided and the results are dependent largely on the size and length of the piping system. With an average-sized system, the first test will require an exhaustion of approximately 25 cu. ft. of free air per renovator per minute if Type A renovators are used. The second test wall require an exhaustion of approximately 50 cu. ft. of free air per open hose per minute. Neither of these tests will insure a plant of sufficient capacity to do effective cleaning where 25-ft. lengths of 1-in. hose can be used or if larger bore than 1-in. hose be used.
If these tests are required with bores larger than 1-in. diameter and the vacuum is maintained the same as before, air exhaustion with 1¹⁄₄-in. open hose will be approximately 70 cu. ft. of free air per open hose, and with 1¹⁄₂-in. hose, approximately 150 cu. ft. per open hose, while, if carpet renovators be used, the vacuum at the renovator would be from 7 to 9 in. of mercury. In either case, the vacuum required to be maintained at the separators is higher than is necessary to produce economical cleaning with either 1¹⁄₄-in. or 1¹⁄₂-in. hose.
Tests with carpet renovators attached to 100 ft. hose lines in number equal to the capacity of the plant, and a vacuum of 4¹⁄₂ in. of mercury at the renovator will result in an exhaustion below that necessary to produce efficient cleaning when bare floor renovators and carpet renovators with shorter hose lines are used, as is likely to occur in actual practice.
Again, open hose tests require a variable length of hose to be used in order to obtain the same air quantity with the proper vacuum at the separator for economical operation.
If 70 cu. ft. of air is desired, as in the case of Class 2 plant (Chapter XII), the hose lengths should be:
50 ft. 1 in. diameter. 12 in. vacuum at separator.
75 ft. 1¹⁄₄ in. diameter. 9 in. vacuum at separator.
125 ft. 1¹⁄₂ in. diameter. 6 in. vacuum at separator.
Any of these lengths would give satisfactory cleaning with one carpet renovator in use, together with sufficient bare floorrenovators to equal the capacity of the plant. This is a possible condition in any plant.
Another method of testing is to measure the actual air passing through a given length of hose and require sufficient vacuum at the separator to produce this flow. This method is open to the objection that variation in the size of the hose will result in considerable variation in the vacuum at the separator and conditions of hose lengths may be such that when carpet renovators are attached to the hose, the vacuum at the renovator will vary according to the resistance offered to the passage of the air by the friction in the hose. With the small hose, the friction will be greatest, and the reduction in the quantity of air passing the renovator from that passing an open hose will result in the greatest reduction in friction loss through the hose and produce the highest vacuum at the renovator. This will cause a widely different vacuum at the renovator with different sizes of hose, each of which passes the same amount of air with the end of hose open.
What is desired in cleaning operations is a certain degree of vacuum at the carpet renovator, with the system operated under the same conditions that will obtain in practical cleaning, and with cleaners of various types attached to hose ends equal in number to the capacity of the plant.
The most rational system of testing is one in which the actual conditions of air quantity and vacuum are measured at the hose ends. This can be obtained by actually attaching cleaning tools to the hose ends and measuring the vacuum within the renovator. However, a wide variation in vacuum will result when the renovator is moved along the carpet, and this variation will be different with different operators and different grades of carpet to such an extent as to render it impossible to actually meet any requirements that may be specified, unless a considerable variation in vacuum is permitted.
It is also possible for an operator to become so expert in the manipulation of the renovators as to be able to meet the specification requirements with a plant which will not give satisfactory results in actual operation.
The most satisfactory method of testing that has been devised is the use of an orifice of proper size fixed to the hose end and measure the vacuum just inside of this orifice. In making such measurements care must be taken that the tube connecting to the vacuum gauge is not inserted in such a manner that the air velocity affects the reading of the vacuum gauge. The shape of orifice must also be carefully specified, as the rounding of the edges of the opening will greatly increase the quantity of air passing a given-sized orifice. The best standard is a sharp-edged orifice in a thin disk which has a coefficient of ingress of approximately 65%.
FIG. 104. VACOMETER FOR USE IN TESTING VACUUM CLEANING SYSTEMS.
FIG. 104. VACOMETER FOR USE IN TESTING VACUUM CLEANING SYSTEMS.
A convenient form of testing appliance based on the orifice test is the vacometer, manufactured by the Spencer Turbine Cleaner Company and shown inFig. 104. This device consists of a spherical aluminum casting, with a 1-in. diameter hole on the equatorial circle, a vacuum gauge being attached to one polar extremity, the other being attached to the end of the hose. A ring having a slip fit is placed around the equatorial circle in which openings varying from ¹⁄₂-in. to ⁷⁄₈-in. diameter are drilled. By turning this ring any of the orifices may be made to register with the opening in the sphere. The opening to which the vacuum gauge is attached is so located that it is not affected by the entering air current, and its readings are not affected by the velocity head.
Experiments with this instrument in connection with a Pitot tube show that a ¹⁄₂-in. diameter orifice is equivalent to a Type A carpet renovator, a ⁵⁄₈-in. orifice to a Type F renovator and a ⁷⁄₈-in. orifice to a bare floor renovator.
With instruments of this type equal in number to the capacity of the plant in sweepers, attached to the ends of the cleaning hose, it is possible to obtain uniform conditions equal to the average results that will be obtained in actual practicewith renovators attached to the hose, without the possibility of expert manipulation of the renovators affecting the results.
The proper orifice to be used in each vacometer during the test will vary with the character of the service for which the plant is designed, and the author recommends the following for each of the classes of plants described inChapter XII:
Class 1. 2-in. mercury, with ¹⁄₂-in. orifice, maximum length of hose to be used in actual cleaning.
Class 2. One-half the inlets ¹⁄₂-in. orifice, 4.5 in. mercury at one orifice attached at end of longest hose desired to use in practice, the remaining ¹⁄₂-in. outlets on shorter hose lengths. The other half of inlets to have ⁷⁄₈-in. orifices open at same time, with longest hose on one-quarter of total inlets and shortest on the balance.
Class 3. All inlets on long hose, one-half with ¹⁄₂-in. orifice, balance with ⁷⁄₈-in.
Class 4. All inlets to have ⁷⁄₈-in. orifice and 1 in. vacuum at vacometer, all hose lines maximum length.