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Theory and practice in the filtration of water
Aug., i916.]
('URR;';NT "I'oPWCS.
277
These are : ~ 1) "l he installation of an efficient grounding system for the removal of static electricity from the machine ; (2) the installation of a suction fan to remove snmt and dust and to prevent the formation of an explosive nfixture of dust and air while the threshing is being carried on; and (3) the installation of a device to act as an automatic fire extinguisher which in the event of fire will not only save the machine but will prevent the flames f r o m spreading to the surrounding grain. The first two of these devices have been tried with successful • results in the field. The automatic fire extinguisher was not constructed until the threshing season had been closed, but it has been tested under severe conditions in the explosion galleries of the Bureau of Mines at Pittsburgh, and in these tests it has operated successfully. It has also been tested under practical threshing conditions at the government f a r m at Arlington, and has proved effective in extinguishing fires which were produced in different types of grain separators there. Blue prints of each of these devices may be secured upon application to the office of Public Roads and Rural Engineering of the department at W~ashington. The best method, the investigations indicate, for carrying off any static electricity that may be produced is to connect wires from all moving parts on the machine to one wire and to ground that wire• The suction fan is arranged to exhaust f r o m above the cylinder and also f r o m beneath the pan. While it is pointed out that there is no way of absolutely demonstrating that either the grounding of the machine or the suction fan actually prevents explosions, the fact remains that no such occurrences have taken place, so far as is known, with separators that were properly equipped in this way. These devices, however, do not remove all danger f r o m fire, for, in addition to electric sparks, foreign materials which find entrance into the separator may start fires, and for this reason the automatic fire extinguisher is regarded as a desirable additional protection. T h e o r y and P r a c t i c e in the F i l t r a t i o n of W a t e r .
W. CLEX~ENCE.
(The Journal of the Institution of Mechanical Engineers, May, I 9 1 6 . ) - - O p e n sand-filters for purifying waters for potable purposes have now been in use for nearly a century, and since 183o they have been continuously used in connection with the London water supply. The first sand-filtration plant, designed by James Simpson for the Chelsea W a t e r Company, consisted of decanting basins in which the raw water could be kept at rest for twelve hours, and open filterbasins in which a layer of fine sand 2 feet 6 inches deep was placed on a bed of gravel of about the same thickness. In the gravel bed brick collecting drains with arched covers were constructed. These large drains were found to induce a too rapid flow of water through the sand immediately over them, and in later practice smaller drains were used which were distributed over the whole area of the floor of the filter to secure an even speed through the bed. VOL. I82, No. Io88----2o
278
CVI~RENT TOPICS.
[J. F. I.
During the last twenty years what is known as the " mechanical filter" has been introduced, in which the arrangement of filtering material differs little in section from that adopted in open sand-beds, but the water under treatment is passed through the materials at a speed from twenty to sixty times greater than that which has been found in practice to represent a safe limit of speed with slow sandfilters in order to obtain complete purification of the water. This limit is generally agreed upon to be from 50 to 75 gallons per square foot per 24 hours, and it is ohvious that if the process of purification is found to be incomplete in the slow filter, on exceeding this speed it must be more so in the rapid filter. With filters of fine sand working at a slow speed it is found that practically all matters in suspension in the water, whether living organisms or silt particles, are retained on the surface of the filtering medium, where they eventually form an impervious layer, and it becomes necessary to remove this in order to restore the permeability of the bed. It has been established in practice that with filters on which a filtering layer is allowed to form the efficiency of the filter is impaired if the layer is disturbed, and that after its complete removal when the filter is cleaned the chemical and bacterial efficiency is not restored until a film has again formed. Much attention has been paid by engineers in recent years to the improvement in the conditions of working and the design of filters, resulting in the formation of two distinct methods o{ practice, based on widely divergent theories. On the one hand, those who support the theory that the bacterial purification of water by filtration is chiefly due to the mechanical action have developed the mechanical filter, in which a fihn is created artificially by the use of a coagulant, and a high speed is adopted. On the other hand, Armand Pusch proved by experiment and observation that the formation of a film on the surface of a filter was a hindrance rather than an aid to purification, and lPusch and Chabal have developed the system of multiple filtration, which is founded on the now ascertained fact that the formation of a film, either natural or artificial, on the surface of the filtering medium is unnecessary and undesirable. N e w Car for Fish Distribution. ANON. (United States Commerce Reports, No. 159, juIy 8, I 9 1 6 . ) - - A new car for the Bureau of Fisheries, designed for carrying live fishes long distances, has lately been completed and is receiving its special equipment preparatory to being placed in commission. The car is entirely of steel and is thoroughly insulated by the latest improved method to insure against heat and cold. It has a length of 6o feet ~ inch over ends of body plates, and a standard width of io feet. The weight of the car wi]:h equipment is I5O,OOO pounds, and is designed to carry a load of 35,ooo pounds. In the centre, running lengthwise on each side, are insulated tanks with a total capacity for I3o ten-gallon cans in which fish are held. During transportation the fish will be fur-
('URR;';NT "I'oPWCS.
277
These are : ~ 1) "l he installation of an efficient grounding system for the removal of static electricity from the machine ; (2) the installation of a suction fan to remove snmt and dust and to prevent the formation of an explosive nfixture of dust and air while the threshing is being carried on; and (3) the installation of a device to act as an automatic fire extinguisher which in the event of fire will not only save the machine but will prevent the flames f r o m spreading to the surrounding grain. The first two of these devices have been tried with successful • results in the field. The automatic fire extinguisher was not constructed until the threshing season had been closed, but it has been tested under severe conditions in the explosion galleries of the Bureau of Mines at Pittsburgh, and in these tests it has operated successfully. It has also been tested under practical threshing conditions at the government f a r m at Arlington, and has proved effective in extinguishing fires which were produced in different types of grain separators there. Blue prints of each of these devices may be secured upon application to the office of Public Roads and Rural Engineering of the department at W~ashington. The best method, the investigations indicate, for carrying off any static electricity that may be produced is to connect wires from all moving parts on the machine to one wire and to ground that wire• The suction fan is arranged to exhaust f r o m above the cylinder and also f r o m beneath the pan. While it is pointed out that there is no way of absolutely demonstrating that either the grounding of the machine or the suction fan actually prevents explosions, the fact remains that no such occurrences have taken place, so far as is known, with separators that were properly equipped in this way. These devices, however, do not remove all danger f r o m fire, for, in addition to electric sparks, foreign materials which find entrance into the separator may start fires, and for this reason the automatic fire extinguisher is regarded as a desirable additional protection. T h e o r y and P r a c t i c e in the F i l t r a t i o n of W a t e r .
W. CLEX~ENCE.
(The Journal of the Institution of Mechanical Engineers, May, I 9 1 6 . ) - - O p e n sand-filters for purifying waters for potable purposes have now been in use for nearly a century, and since 183o they have been continuously used in connection with the London water supply. The first sand-filtration plant, designed by James Simpson for the Chelsea W a t e r Company, consisted of decanting basins in which the raw water could be kept at rest for twelve hours, and open filterbasins in which a layer of fine sand 2 feet 6 inches deep was placed on a bed of gravel of about the same thickness. In the gravel bed brick collecting drains with arched covers were constructed. These large drains were found to induce a too rapid flow of water through the sand immediately over them, and in later practice smaller drains were used which were distributed over the whole area of the floor of the filter to secure an even speed through the bed. VOL. I82, No. Io88----2o
278
CVI~RENT TOPICS.
[J. F. I.
During the last twenty years what is known as the " mechanical filter" has been introduced, in which the arrangement of filtering material differs little in section from that adopted in open sand-beds, but the water under treatment is passed through the materials at a speed from twenty to sixty times greater than that which has been found in practice to represent a safe limit of speed with slow sandfilters in order to obtain complete purification of the water. This limit is generally agreed upon to be from 50 to 75 gallons per square foot per 24 hours, and it is ohvious that if the process of purification is found to be incomplete in the slow filter, on exceeding this speed it must be more so in the rapid filter. With filters of fine sand working at a slow speed it is found that practically all matters in suspension in the water, whether living organisms or silt particles, are retained on the surface of the filtering medium, where they eventually form an impervious layer, and it becomes necessary to remove this in order to restore the permeability of the bed. It has been established in practice that with filters on which a filtering layer is allowed to form the efficiency of the filter is impaired if the layer is disturbed, and that after its complete removal when the filter is cleaned the chemical and bacterial efficiency is not restored until a film has again formed. Much attention has been paid by engineers in recent years to the improvement in the conditions of working and the design of filters, resulting in the formation of two distinct methods o{ practice, based on widely divergent theories. On the one hand, those who support the theory that the bacterial purification of water by filtration is chiefly due to the mechanical action have developed the mechanical filter, in which a fihn is created artificially by the use of a coagulant, and a high speed is adopted. On the other hand, Armand Pusch proved by experiment and observation that the formation of a film on the surface of a filter was a hindrance rather than an aid to purification, and lPusch and Chabal have developed the system of multiple filtration, which is founded on the now ascertained fact that the formation of a film, either natural or artificial, on the surface of the filtering medium is unnecessary and undesirable. N e w Car for Fish Distribution. ANON. (United States Commerce Reports, No. 159, juIy 8, I 9 1 6 . ) - - A new car for the Bureau of Fisheries, designed for carrying live fishes long distances, has lately been completed and is receiving its special equipment preparatory to being placed in commission. The car is entirely of steel and is thoroughly insulated by the latest improved method to insure against heat and cold. It has a length of 6o feet ~ inch over ends of body plates, and a standard width of io feet. The weight of the car wi]:h equipment is I5O,OOO pounds, and is designed to carry a load of 35,ooo pounds. In the centre, running lengthwise on each side, are insulated tanks with a total capacity for I3o ten-gallon cans in which fish are held. During transportation the fish will be fur-