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 floor renovators 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%.
