D: 1901.]
PUBLIC HEALTH.
[No. 10.
919
ter passing through the 12" pipe would be about thirty-two times that passing through the 3" pipe. But if the same quantity flowed through both then the current in the 3" pipe, being more concentrated, would flow more rapidly than that in the partially filled 12" pipe.
These considerations would lead to the conclusion that the best size to be used for any house-drain would be that which would just suffice to carry off the sewage with the pipe not less than half full. Within certain limitations, this is the case.
In the case of street-sewers draining large districts, from which the flow of sewage is comparatively regular and capable of estimation, the size of sewer may be calculated with some approach to precision. In house-drains, however, such precision is impracticable. The rate of flow is irregular and the quantity of sewage depends upon the habits of the inmates. Were the size of a house-drain calculated to carry off even a most liberal water supply, which is, for practical purposes, the measure of the sewage, it would be found, in the vast majority of cases, to be much less than that which experience has shown to be applicable in practice. It has been found that a house-drain less than a certain size is inconveniently liable to stoppages, caused by extraneous matters, such as rags, paper, and the like, which occasionally find their way into the best managed house-drains.
Difficulties in estimating proper size of house-drain.
I. The minimum size of house-drain is usually fixed at from four to six inches in diameter. A four-inch drain, constructed in the usual manner, is probably somewhat small as a minimum; and a six-inch somewhat large. A diameter of five inches, were this size readily obtainable, would be a better minimum.
J. Whenever the minimum size will suffice it should be used. Indeed, subject to the limit laid down in the last preceding paragraph and to certain conditions to be set forth later on, the smaller the house-drain the better. The use of unnecessarily large house-drains amounts to an abandonment of the self-cleansing principle. If a drain is so large that the normal flow of sewage cannot fill it to a sufficient depth to establish a self-cleansing velocity, deposit takes place and goes on, either till the pipe is choked and the sewage escapes, through leaks, to the sub-soil, or until the deposit has accumulated sufficiently to reduce the area of the sewage-way to that which will establish a current sufficiently rapid to prevent further deposit.
K. In order that the size of house-drains may be reduced to the minimum practicable, in each instance, rain-water should be excluded from them as far as possible. Rain-water cannot, however, be wholly excluded from house-drains. Many uncovered surfaces, such as backyards, receive slops and foul-water in the course of daily use, and this must be carried off by the house-drains. A duplicate set of drains for such areas, one for sewage and the other for rain-water, would be a costly complication, and there would be no security that each set would be used for its proper purpose only. Some sewage would
1.
Desirability of exclusion of rain-water from house-drain.
Page 45
Page 46
D: 1901.]
PUBLIC HEALTH.
[No. 10.
919
ter passing through the 12" pipe would be about thirty-two times that ssing through the 3" pipe. But if the same quantity flowed through both then the current in the 3" pipe, being more concentrated, would flow rapidly than that in the partially filled 12" pipe.
ore
pipe for
These considerations would lead to the conclusion that the best size to Best size of ased for any house-drain would be that which would just suffice to carry off he sewage with the pipe not less than half full. Within certain limitations, This is the case.
size
proper In the case of
H. In the case of street-sewers draining large districts, from which the flow of sewage is comparatively regular and capable of estimation, the of sewer may be calculated with some approach to precision. house-drains, however, such precision is impracticable. The rate of flow is regular and the quantity of sewage depends upon the habits of the inmates. Were the size of a house-drain calculated to carry/off even a most liberal water supply, which is, for practical purposes, the measure of the sewage, it would be found, in the vast majority of cases, to be much less than that which experience has shown to be applicable in practice. It has been found that a house-drain less than a certain size is inconveniently liable to stoppages, caused by extraneous matters, such as rags, paper, and the like, which occasionally find their way into the best managed house-drains.
house-drain.
Difficulties in estimating proper size of house-drain,
drain.
I. The minimum size of house-drain is usually fixed at from four to six Minimum inches in diameter. A four-inch drain, constructed in the usual manner, is size of house- probably somewhat small as a minimum; and a six-inch somewhat large. A diameter of five inches, were this size readily obtainable, would be a better minimum.
house-drain.
J. Whenever the minimum size will suffice it should be used. Indeed, Objections to ubject to the limit laid down in the last preceding paragraph and to certain use of large conditions to be set forth later on, the smaller the house-drain the better. The ase of unnecessarily large house-drains amounts to an abandonment of the self- cleansing principle. If a drain is so large that the normal flow of sewage Cannot fill it to a sufficient depth to establish a self-cleansing velocity, deposit takes place and goes on, either till the pipe is choked and the sewage escapes, through leaks, to the sub-soil, or until the deposit has accumulated sufficiently to reduce the area
sufficiently of the sewage-way to that which will establish a current
Sufficiently rapid to prevent further deposit.
K. In order that the size of house-drains may be reduced to the minimum practicable, in each instance, rain-water should be excluded from them as far as possible. Rain-water cannot, however, be wholly excluded from house- drains. Many uncovered surfaces, such as backyards, receive slops and foul- water in the course of daily use, and this must be carried off by the house- drains. A duplicate set of drains for such areas, one for sewage and the other for fain-water, would be a costly complication, and there would be no security hat each set would be used for its proper purpose only. Some sewage would
1.
Desirability of exclusion of rain-water from house- drain.
Page 45Page 46
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