CHAPTER VIII.Separators.

The appliances which remove the dust from the air current which has carried it through the hose and pipe lines, in order to prevent damage to the vacuum producer, play an important part in the make-up of a vacuum cleaning system.

—Separators may be divided into two classes according to their use:

1. Partial separators, which must be used in conjunction with another separator in order to effect a complete removal of the dust from the air. These separators are again divided into two sub-classes,i. e., primary, or those removing the heavy particles of dust and dirt only, and secondary, or those removing the finer particles of dirt which have passed through the primary separator.

2. Complete separators, or those in which the removal of both the heavy and the finer particles of dust is effected in a single separator.

Separators may also be classified, according to the method employed in effecting the separation, into dry separators in which all operations are effected without the use of liquid, and wet separators in which water is employed in the removal of the dust.

—Primary separators are nearly always operated as dry separators and depend largely on centrifugal force to effect the separation. The first type of primary separator used by the Vacuum Cleaner Company is illustrated inFig. 67. This consists of a cylindrical tank, with hopper bottom, containing an inner cylinder fixed to the top head. The dust-laden air enters the outer cylinder near the top on a tangent to the cylinder. The centrifugal action set up by the air striking the curved surface of the outer cylinder tends to keep theheavy dirt near the outside of same, and as it falls towards the bottom the velocity is reduced and its ability to carry the dust is lost. When the air passes below the inner cylinder the velocity is almost entirely destroyed and all but the very lightest of the dust particles fall to the bottom, while the air and the light dust particles find their way out of the separator through the opening in the center at the top.

FIG. 67. EARLY TYPE OF PRIMARY SEPARATOR USED BY VACUUM CLEANER COMPANY.FIG. 68. PRIMARY SEPARATOR USED BY THE SANITARY DEVICES MANUFACTURING COMPANY.

FIG. 67. EARLY TYPE OF PRIMARY SEPARATOR USED BY VACUUM CLEANER COMPANY.

FIG. 68. PRIMARY SEPARATOR USED BY THE SANITARY DEVICES MANUFACTURING COMPANY.

The primary separator used by the Sanitary Devices Manufacturing Company is illustrated inFig. 68. The inner centrifugal cylinder is omitted and the air enters through an elbow in the top of the separator, near its outer extremity, which is turned at such an angle that the air is given a whirling motionresulting in the dust being separated much the same as in the case of the Vacuum Cleaner Company’s apparatus.

Either of these separators will remove from 95% to 98% of the dirt that ordinarily comes to them through the pipe lines and are about equally efficient.

FIG. 69. PRIMARY SEPARATOR USED BY THE GENERAL COMPRESSED AIR AND VACUUM CLEANING COMPANY.FIG. 70. PRIMARY SEPARATOR MADE BY THE BLAISDELL ENGINEERING COMPANY.

FIG. 69. PRIMARY SEPARATOR USED BY THE GENERAL COMPRESSED AIR AND VACUUM CLEANING COMPANY.

FIG. 70. PRIMARY SEPARATOR MADE BY THE BLAISDELL ENGINEERING COMPANY.

The separator illustrated inFig. 69was used by the General Compressed Air and Vacuum Cleaning Company. The entering air is led to the center near the bottom and is then released through two branches curved to give the air a whirling motion. The clean air is removed from the center of the separator near the top. This separator is not as effective in its removal of dirt as either of the former types, owing to the entering air being introduced near the bottom. This tends to keep the air and the dust in the bottom of the separator continually stirred up, also the curved inlets give the air more of a radial than a tangential motion and there is less separation due to centrifugal action.

The separator illustrated inFig. 70is made by the Blaisdell Engineering Company. In this separator the inner centrifugal cylinder of the Vacuum Cleaner Company’s separator is replaced by a spiral extending nearly to the outlet in the center of the top. This arrangement tends to prevent the reduction in the air velocity and to limit its effectiveness in the removal of dust.

Separators similar to the Sanitary separator have been manufactured by many firms producing vacuum cleaning systems. These all differ somewhat in details of construction but the principle involved,i. e., centrifugal force and reduction in air velocity, is the same in all cases.

With vacuum producers in which there are no close clearances or rubbing contacts, these are the only separators used. The finer particles of dust passing these separators are carried harmlessly through the vacuum producer and through the exhaust to the outer atmosphere or to the chimney or other flue where they are effectively sterilized.

—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 inFig. 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 inFig. 72was 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.

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 entirelyoutside 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.

FIG. 73. SECONDARY SEPARATOR USED BY THE SANITARY DEVICES MANUFACTURING COMPANY.

FIG. 74. TYPE OF DRY SEPARATOR USED AS SECONDARY SEPARATOR.

The separator used by the Sanitary Devices Manufacturing Company differs from those already described in that the air and water are mixed before they enter the separator and the air comes into the separator above the water line. The air enters the pipe “a” (Fig. 73) and passes to the aspirator “b,” which is connected to the separator by the pipe “d” below the water line and the pipe “e” above the water line. The excess of vacuum in the separator draws the water out of the aspirator and its pipe connections until the water line in this pipe is lowered below the top of the horizontal portion of the piping, when the air bubbles up through the demonstrator glass “c” and passes into the separator through the pipe “e.” The filling of the vertical pipe leading to “c” with air causes the static head of the water in the separator to produce a flow of water through the pipe “d” into the aspirator “b.” This is formed in the shape of a nozzle and the water enters in the form of a spray and thoroughly mixes with the air. The cleansing action of this water spray has been found to be very effective in removal of all fine dust and this separator has been found to be the most effective wet separator ever produced.

While the wet separator when properly designed will effectively remove the finest of dust, greasy soot will not emulsify with the water and its removal is practically impossible. Fortunately, this form of material in the finely-divided condition in which it passes the primary separator is not gritty and does not produce injurious effect on the vacuum producer.

The wet separator is also at a disadvantage in that there is a loss of vacuum in passing through same equal to the head of water that is carried between the inlet and the surface of the water. This generally amounts to nearly 2 in. mercury.

Means must be provided to observe the height of the water in the wet separator. For this purpose a glass window in the side of the separator has been found to be the most effective. The use of an ordinary gauge glass such as is used on boilers has been tried, but it has been found that they readily become so clouded by the action of the muddy water as to render them useless while the constant agitation of the water against the window when the system is in operation tends to keep the glass clean.

Dry separators have been used for secondary separators to a limited extent. All of these contained a bag made of canvas or some other fabric. The separator illustrated inFig. 74contains a bag made of drilling which is slightly smaller than the inner diameter of the cylindrical casing of the separator. The air enters the inside of the bag, inflating it, and passes through the bag and out through the opening in one side of the casing. A wire guard is placed over this opening to prevent the bag being drawn against the opening and thus rendering only a small portion of it effective.

These bags offer very little resistance to the passage of the air when they are clean but they soon become filled with dust and produce an increased resistance which, if neglected, may result in so great a difference in pressure as to hinder the action of the system and result in the rupture of the bag, letting the dust into the vacuum producer.

Some trouble has been experienced in finding a suitable material through which the dust will not pass. Hush cloth, such as used on dining tables, has been found to be the best materialfor this purpose. Better results are obtained by passing the air from the outside of the bag towards the inside than when the air is passed as indicated inFig. 74. When this arrangement is adopted, it is necessary to stretch the bag over a metal screen or frame in order to prevent collapse.

—Complete separators are of two classes,i. e., dry and wet. The first complete separator that the author has knowledge of was used by the Vacuum Cleaner Company, in the form of a cylindrical tank and contained centrifugal cylinder and also a perforated plate. It was practically a combination of the separators indicated inFigs. 67and71. This separator was installed in connection with a small rotary pump and mounted on a truck. It worked very well until it became filled with dirt when, in one case, the entire contents were ejected into an apartment in which it was being used. This separator was then rebuilt in the form shown inFig. 75, the bag being made of hush cloth stretched over a wire screen. The air enters the cylinder tangentially and much of the separationis accomplished by centrifugal force, the remainder of the dust being removed as the air passes through the bag. This separator was successfully used as long as this company continued to manufacture such apparatus.

Another form of complete separator quite similar to that above described has recently been brought out by the Electric Renovator Manufacturing Company and is shown in section inFig. 76. The air enters this separator tangentially below the line of the dust bag, which is made of muslin folded back and forward over a set of concentric cylinders thus giving a large area for the passage of the air. Being entirely above the line of the entering air, none of the heavy dirt strikes the bag and what dirt is caught on the bag is on the lower side of same and is shaken off every time the bag is agitated. This agitation occurs every time there is any change in the volume of air passing the separator, and when these separators are used in connection with fan type of exhausters there is a constant surging whenever the exhauster is operated with a small volume of air passing. This tends to keep the bag clean automatically.

FIG. 75. FORM OF COMPLETE SEPARATOR USED BY THE VACUUM CLEANER COMPANY.

The separator illustrated inFig. 77is manufactured by the American Radiator Company. The air enters this apparatus through the pipe in the center and passes directly down to the bottom, the velocity being gradually reduced due to the expansion of the air as it passes down the cone-shaped inlet, the heavy dirt falling to the bottom. The air then passes up along the inner surface of the cylindrical shell and thence through the bag, which is stretched over a screen, to the outlet. In this separator we see the first case in which centrifugal action is not utilized in separating the heavy dust, the makers evidently considering the reduction of air velocity and the action of gravitation to be ample. This bag is arranged to permit the air passage from the outside towards the inside and it is tapered to allow the dirt to fall off. The vacuum gauge is connected to the inner and outer sides of the bag by means of a three-way cock to permit of measuring the difference in vacuum between the inside and outside of the bag to determine when the bag is in need of cleaning, which is accomplished by a reversal of the air current through the bag. This is quite necessary in order to keep the separator always in an efficient condition.

FIG. 76. COMPLETE SEPARATOR BROUGHT OUT BY THE ELECTRIC RENOVATOR MANUFACTURING COMPANY.

FIG. 77. COMPLETE SEPARATOR MADE BY THE AMERICAN RADIATOR COMPANY.

A separator was devised by the Sanitary Devices Manufacturing Company in which the bag was held extended by a wire ring having a weighted rod passing out through the top of the separator attached thereto. When the bag became clogged the difference in pressure on the two sides would result in a tendency of the bag to collapse and the rod would be raised up out of the separator, indicating that cleaning was necessary, which could be easily accomplished by drawing the rod up and down a few times thus shaking the dust off the bag. This separator never came into general use, although its arrangement was ingenious and should have been easy to operate.

The great difficulty with all bags which must be cleaned periodically is that they are almost universally neglected even when there is a visual indicator to show the accumulation of dirt, and when it becomes necessary to manipulate a three-way cock in order to ascertain when this cleaning must be done it will seldom if ever be attended to. A bag that will clean itself, such as the Capitol Invincible, is shown inFig. 76.

The separator used by one manufacturer consists of a simple cylindrical tank into which the air is blown tangentially, with a screen near the top, the whole forming a base for the vacuum producer. This separator does not remove any but the heaviest dirt and is suitable for use only with a vacuum producer having very large clearances and in locations where the discharge of considerable dirt into the atmosphere is not objectionable.

—The only total wet separator which is in commercial use is manufactured by the American Rotary Valve Company. This separator is contained in the base of the vacuum producer and is provided with a screen near the point of entrance of the dust-laden air, which screen is cleaned by a mechanically-driven bristle brush. When the water in theseparator becomes foul, the contents of the separator are discharged direct to the sewer by means of compressed air. If this separator receives proper attention it makes the most sanitary arrangement that has been introduced in the vacuum cleaning line to date. However, the separator should be emptied at frequent intervals or the volume of solid matter contained in the same will become so great that there will not be enough water present to flush the sewer and stoppage is likely. These separators are often neglected until the contents become of the consistency of mortar or molasses which is not a fit substance to discharge into a sewerage system.

There is still another form of apparatus used in connection with vacuum cleaning systems which should be called an emulsifier rather than a separator. That is the type used with the Rotrex and the Palm systems. The dust is mixed with water when it first enters the pump chamber, a screen being used to remove the lint and larger particles of dirt and then the mud produced by the combination of the dust and water is passed through the pump along with the air. The air and muddy water are separated on the discharge side of the vacuum producer. In many cases where the exhaust pipe is long, there is considerable back pressure on the discharge which is often sufficient to force the seals in traps on the sewerage system, allowing sewer gas to be discharged into the building in which the cleaning system is installed. No means are provided for automatically cleaning the screen used in these appliances and the author knows of cases where the screen has become so completely clogged with lint that its removal from the machine was necessary in order to render the operation of the cleaning tools possible.

When dry separators are used, the manual removal of the dry dirt accumulated is necessary and is an objectionable as well as unsanitary operation. The author considers that the ideal arrangement of separator would be one in which the dirt can all be emulsified with water and retained in the separator, only the air passing through the vacuum producer, and in which the contents of the separator would be discharged automatically to the sewer when the density of this mixture becomes as heavy aswill readily run through the sewer. This discharge should be of sufficient volume to completely fill an ordinary house sewer in order to insure a thorough flushing of the drain, and should be discharged into the sewer under atmospheric pressure in order to guard against the forcing of water seals in any of the plumbing fixtures.

FIG. 77a. INTERIOR CONSTRUCTION OF DUNN VACUUM CLEANING MACHINE.

A separator of this type has recently been patented by E. D. Dunn, originator of the Dunn Locke system. It is illustrated inFig. 77a. The action of the separator is as follows: After starting the motor and turning on a small quantity of water, a vacuum is produced in one tank and through a system of piping to the cleaning implement in use. The dust and dirt collected by the implement is saturated as it approaches theplant and in this saturated condition enters the bottom of a body of water in the tank.

When the accumulating dirt and water reach a certain level a valve is automatically operated which closes the tank’s communication with the vacuum pump and allows its contents to flow off to the sewer by gravity. The mechanism for operating the valve is rather unique and includes a float which, on rising with the water, makes a positive electrical contact, as shown in the figure. In this illustration one tank is about to discharge and the other tank is about to become operative. The electrical contact causes the core of the magnet at O¹ to rise, making the lever, K, turn over, which action opens one valve and closes the other. In this way the tanks alternately partly fill and empty their collections of water and sweepings.

This system has not as yet been in commercial use for a sufficient length of time to insure its successful operation, and the author does not consider the passing of dirt and water through ordinary check valves to be commercially possible without rendering these checks inoperative.

Check valves have been used where partial wet and dry separators are operated in tandem to prevent drawing water into the dry separator, in the event of the plant being shut down with all inlets on the pipe line closed. In such a case, the leakage through the pump into the wet separator may raise the pressure in this separator faster than leakage on the pipe line raises the pressure in the dry separator.

This is accomplished by providing a small connection between the upper part of the two separators, fitted with a check valve opening towards the dry separator. When the vacuum producer is in operation, the vacuum in the wet separator is approximately 2 in. greater than that in the dry and the check is held closed. When the vacuum producer is stopped and the vacuum in the wet separator falls faster than in the dry separator, this check opens and clean air passes from the wet to the dry separator. When operating under these conditions, the action of the check valve is satisfactory. However, the author has known of cases where the check leaked and when this happened the check was immediately clogged by the dust-laden air from the dry separator.

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