924
standard grade.
No. 10.] THE ORDINANCES OF HONGKONG: [A.D. 1901
of the drain nearest to the outlet, rather than in the part nearest to the inlet, and in the main trunk of the drain rather than in the branches...
NOTE.-The available fall in a house drain, 100 feet long, is 2 feet 6 inches or one in forty. It will be better to make the first thirty feet from the inlet with a fall of 1 in 30, and the remaining length of 70 feet with a fall of 1 in 46.66, than to give a uniform fall throughout.
100'
e.g. (1.)
1 IN 30
A
B 1 IN 40
1 IN 46'8
It is clear that an obstruction at A would be more easily removed than one at B, in the pipe of uniform gradient, because it would have a greater head of water behind it; and in flowing from the inlet to it, the stream will have attained a certain momentum, tending to carry it on, through the flatter part of the pipe.
e.g. (2.)
40'
60'
90'
A B is a drain 90 feet long, with an available fall of 3 feet, between A and B. At C, distant 60 feet from A, there is a branch C D 40 feet long D being at the same level as B.
If the main-drain AB were given a uniform fall of 1 in 30, then C would be 1 foot below B and D Then CD would have a fall of 1 in 40 only. The proper course to pursue would be to give CD a fall of 1 in 30, or 1′ 4′′ in all. BC would then have a fall of 1′ 4′′ in 30 feet, or 1 in 22.1, and CA a fall of 1.98 in 60 feet, or 1 in 36.
Requiring automatic flush tank in case of fall less than standard grade.
Direction and grading of house-drain.
16. Whenever the gradient of any portion of a drain is less than 1 in 30, the Board may, in its discretion, require an automatic flush tank or any other suitable contrivance for attaining an effective flush to be used.
17. All changes of direction in house-drains shall be made by means of properly curved pipes or by half channels in man-holes, and between the points at which any change of direction occurs all house-drains shall be laid in straight lines and regular grades from point to point.
NOTE.-Inasmuch as changes of direction are the points at which obstructions most frequently occur, and for the purpose of removing obstructions generally, householders will do well to provide, at each change of direction, a manhole, giving access to the drain. For this purpose the manhole should be made 3 feet by 1 foot 6 inches to the surface or a depth of 5 feet above the drain. Beyond this depth the manhole may be narrowed
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Page 51
924
standard grade.
No. 10.] THE ORDINANCES OF HONGKONG: [A.D. 1901
w
of the drain nearest to the outlet, rather than in the part nearest to the inlet, and in the main trunk of the drain rather than in the branches...
NOTE.-The available fall in a house drain, 100 feet long, is 2 feet 6 inches or one in forty. It will be better to make the first thirty feet from the inlet with a fall foot, or 1 in 30, and the remaining length of 70 feet with a fall of 1 in 46 66, than to give an uniform fall throughout.
100'
e.g. (1.)
Ն
1 IN 30
A
B 1 IN 40
1 IN 46'8
It is clear that an obstruction at A would be more easily removed than one at B, in the pipe of uniform gradient, because it would have a greater head of water behind it; and in flowing from the inlet to it, the stream will have attained a certain momentum, tending to carry it on, through the flatter part of the pipe.
e.g. (2.)
40'
60o
B
A
90'
A B is a drain 90 feet long, with an available fall of 3 feet, between A and B. At C, distant 60 feet from 4, there is a branch C D 40 feet long D being at the same level as B.
If the main-drain AB were given an uniform fall of 1 in 30, then C would be 1 foot below B and D Then CD) would have a fall of 1 in 40 only. The proper course to pursue would be to give CD a fall of 1 in 30, or 1′ 4′′ in all. BC would then have a fall of 1′ 4′′ in 30 feet, or 1 in 221, and CA a fall of 198 in 60 feet, or 1 in 36.
Requiring automatic
flush tank in
case of fall
less than
standard grade.
Direction and.. grading of house-drain.
16. Whenever the gradient of any portion of a drain is less than 1 in 30, the Board may, in its discretion, require an automatic flush tank or any other suitable contrivance for attaining an effective flush to be used.
17. All changes of direction in house-drains shall be made by means of properly curved pipes or by half channels in man-holes, and between the points at which any change of direction occurs all house-drains shall be laid in straight lines and regular grades from point to point.
NOTE.-Inasmuch as changes of direction are the points at which obstructions most fre quently occur, and for the purpose of removing obstructions generally, householders) wil do well to provide, at each change of direction, a manhole, giving access to the drain. For this purpose the manhole should be made 3 feet by 1 foot 6 inches to the surface or a depth of 5 feet above the drain. Beyond this depth the manhole may be narrowed
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