In Table XXXVI figures above the diagonal line refer to standard wrought pipes the diameters of which vary a little from the actual diameters given. In the lower part of the table the figures refer to pipes of the actual sizes given.

The table is used in the following manner: If it is desired to know the number of 3/4-inch taps or pipes that will equal in discharging capacity a 2-inch pipe, glance down the column marked 2 to the intersection of the line in the first column marked 3/4. This shows that it requires fourteen 3/4-inch taps or pipes to equal one 2-inch pipe. To find the number of pipes of one size that equals the discharging capacity of another, in the lower part of the table, follow down the columns the size of the smaller pipe until it intersects the line of the larger one. Thus to find the number of 2-inch pipes that equal a 10-inch pipe, follow down the column marked 2 to where it intersects the line marked 10 and it will be found that 80.4 two-inch pipes equal in discharging capacity one 10-inch pipe.

Hotels, clubs, hospitals and other buildings that require an uninterrupted supply of water should when possible be provided with two service pipes. Each service pipe should be of sufficient capacity to supply the entire building and should be connected to the street main in different streets. The service pipes should then be cross connected within the building, so that if water is shut off from one city main an adequate supply can be drawn from the other one.

Service pipes are usually provided with a stop cock located at the curb. This curb cock gives the water company control of the supply within a building, so that water can be shut off at any time without digging down to the corporation cock or entering the premises.

Sizes Of Water Pipes

Water supply systems should be so proportioned that a plentiful supply of water at low velocity can be had at all fixtures. If pipes are too small, there will be the annoyance of one faucet robbing another, also, owing to the high velocity of flow when water is being drawn, a disagreeable singing or hissing noise will be heard in the pipes.

In proportioning a water supply system the chief condition to be ascertained is the probable number of fixtures at which water will simultaneously be drawn. In residences and other buildings with comparatively few fixtures the supply pipes should be proportioned to supply all the fixtures simultaneously. In hotels, apartment houses and like buildings, however, such provision is unnecessary. It is not probable that more than one fixture at a time will be in use in a bath room, nor is it probable that more than one fixture at a time will be used in the kitchen, although it is quite probable that fixtures in kitchen and bath room will be simultaneously used; hence, if provision be made to supply at the same time one fixture in each group within a building, the pipes will be of sufficient capacity to meet all requirements.

The largest pipe used to supply any fixture is 3/4 inch diameter and the average size 1/2 inch in diameter. Faucets and cocks for 3/4-inch pipes seldom have an unobstructed waterway larger than 1/2-inch diameter, while the waterway of 1/2-inch cocks and faucets seldom exceeds 3/8 inch in diameter; hence, if in all water pipes an allowance is made of the sectional area of a 1/2-inch pipe for one fixture in each group, the system will be so proportioned that an adequate supply of water at low velocity will be had at all fixtures. An exception to the foregoing statements must be made in the case of public toilet rooms and batteries of wash basins in factories or other institutions. All the fixtures in such batteries might be used at the same time and an allowance of the sectional area of a 1/2-inch pipe for each fixture should be made.

Example

What size of water main will be required for an apartment house of fifteen families, each family being provided with bath room and kitchen?

Solution

Fifteen bath rooms and fifteen kitchens equal thirty-groups of fixtures to be supplied at once, and allowing the sectional area of a 1/2-inch pipe for each group of fixtures requires a pipe with a capacity of thirty 1/2-inch pipes. From Table XXXVI will be found that a 2-inch standard pipe has the required capacity.

Example II

What size of service pipe will be required to supply a hotel equipped with 280 bath rooms and 20 other groups of fixtures?

Solution

280 + 20 = 300, and according to Table XXXVI, about a 4 1/2-inch pipe would equal in capacity three hundred 1/2-inch pipes.