TABLE XVIII.

SHOWING INCREASED FRICTIONAL HEAD REQUIRED FOR CURVES IN VARIOUS CASES.

In the columns of loss of grade per 100 feet can be found the increased fall necessary, under the supposition that, on ordinary curves, n is increased from .011 to .013, and on sharp curves from .011 to 015.

It will be observed that when n=.013 the value of C is decreased to about eighty per cent. in all cases. Recurring to the general formula of Chezy, which for the ordinary range of diameter and velocity, becomes, approximately,

V=100√RS

We may write for ordinary curves,

V=80/RS'

Or, since in each case the hydraulic mean radius when the

In pipe sewers, however, the roughness is somewhat dependent on the ratio of the radius of the curve to diameter of the pipe.

Empirical Formula.-The following formula will give good results in pipe sewers:

roughness.

-length of curve in feet.

d-diameter of sewer in feet.

r-radius of axis of curve in feet.

H-loss of head for curve in feet due to increased

H in the above formula does not represent the total fall required for the curve, but the excess of fall necessary over that if the sewer were straight, and the flow had an equal velocity.

CHAPTER VII.

MATERIAL AND ACCESSORIES.

Sewer Pipes.-Salt-glazed, vitrified earthenware is the best material thus far produced for sewer pipes. It forms a smooth, impervious conduit, is not affected by the sewage, and is practically indestructible. It is manufactured in all sizes, from two inches to two feet in diameter, and in convenient forms for special purposes. The pieces are usually either two or three feet in length. They are either made with a "bell" at one end for holding the "spigot" end of the adjoining piece in laying, or as simple cylinders, with a separate collar for making the joint. The socket and spigot pipe is usually preferred. Pieces with Y branches should be placed wherever a house drain is to be connected with the sewer.

Tests of twelve-inch sewer pipe were made at Boston by Chief Engineer W. H. Bradley, with the following results:

"The pipes were three feet long and without sockets, except as noted.

The crushing test was made by bedding the pipes, horizontally, half their depth in sand and crushing them by a weight applied uniformly along the length on the top; figures are pounds per foot of length (average of three pipes).

"The breaking test was made by supporting ends of pipes on two blocks two feet six inches apart and applying weight at center; figures are total weight (one test).

The abrasion test was made by applying a section 1⁄2 inch square, loaded with 20 lbs., to a revolving grindstone three feet in diameter, kept wet and clean; figures are revolutions necessary, 1st, to remove glazing; 2nd, to grind away 1-10 of total thickness including glazing (average of two tests). ”

D. L. King, Secretary, Akron Co., Ohio.

D. W. Lewis, Agent, Tallmage Co., Ohio.

4606 33

Hill Sewer Pipe Co.; Ohio.

40.4

1.04

1880

75

793

""

Slip Glazed

40.0

I. IO

2.17

2052

4299

12

90

The capacity of vitrified salt-glazed sewer pipe to resist abrasion is very marked.

Hand-Holes.-A "hand-hole" is a piece of pipe provided with a detachable section. See Fig. 2. These hand-holes afford the means of removing obstructions without breaking the pipe. They are usually laid at intervals of about one hundred feet. Their use may be dispensed with and the sewer may be opened when necessary by removing the cap from a Y branch.

FIG. 2.

Lamp-Holes.-At intervals a T should be placed in the sewer and a stand-pipe carried to the surface, forming an opening where the action of the sewer may be observed. See Plate I. Part of them may stop just beneath the pavement and be covered with a light casting, shown in Plate I, and at longer intervals part of them may be carried to the surface and protected with a cast iron cover.

Fresh Air Inlets.-These will answer in place of manholes in some cases when the distance between the junction of two or more sewers is considerable. They afford facilities for inspection, and have the advantage of preserving the flow of sewage in its proper sectional form and precluding the possibility of deposit. They are, however, not as available as points from which cleaning tools can be inserted into the sewer. They should be covered with a perforated cast-iron cover, similar to that shown in Plate II, to assist in the ventilation of the sewer. They can be very cheaply constructed.

They should always be thus brought to the surface when it is proposed to extend a line of sewer in the near future, and can