—With vacuum producers having close clearances or rubbing parts in contact with each other and the air exhausted, further separation of the finer dust particles is necessary. To accomplish this, secondary separators are used.
All of the early systems used a wet separator as a secondary separator. That used by the Vacuum Cleaner Company is illustrated in [Fig. 71]. It consists of a cylindrical tank partially filled with water, with a diaphragm perforated in the central portion and fixed in place below the water line, and an inverted frustrum of a cone placed just above the water line. The air enters the separator below the water line and passes up through the water in the form of small bubbles which are broken up into still smaller bubbles on passing through the perforations in the diaphragm. This action is very essential to the thorough cleansing of the air, as large bubbles of air may contain entrapped dust which will pass through the water and out into the vacuum producer. The inverted frustrum of a cone is intended to prevent any entrained water passing out of the separator with the air. This separator has always given satisfactory results when used in connection with reciprocating pumps.
The separator illustrated in [Fig. 72] was manufactured by the General Compressed Air and Vacuum Cleaning Company. The air enters the separator through the pipe curved downward and escapes at the center below the water line. It then rises in the form of bubbles and most of it strikes the under side of the ribbed aluminum disc “a,” which is intended to float on the surface of the water, and passes along the ribbed under surface of this disc, escaping into the upper part of the separator around the edge.
FIG. 71. SECONDARY SEPARATOR USED BY THE VACUUM CLEANER COMPANY.
FIG. 72. SECONDARY SEPARATOR USED BY THE GENERAL COMPRESSED AIR AND VACUUM CLEANING COMPANY.
The clean air passes out of the top of the separator to the vacuum producer. The successful operation of this separator is dependent on the freedom of motion of the disc “a,” which will always keep it on the surface of the water, and on all of the air passing up through the water under the disc.
Should the disc become caught on the supporting pipe the violent agitation of the water, which occurs when the system is in operation, will cause the disc to be left high and dry above the water at times, and submerged at other times. When this disc is above the water line it will not break up any of the large bubbles. Also, when there is a large quantity of air passing through the separator, there is great likelihood that considerable of the air bubbles will pass up through the water entirely outside of the disc and these bubbles will not be broken up. This separator has given somewhat unsatisfactory results in some installations tested by the author.
