80. Globe valves and globe checks retard the flow of water too much, and, therefore, should not be used for low-pressure work, nor where a loss of pressure would be objectionable. Gate valves, or plug cocks, should be used instead, as they afford a freer passage for the liquid.

81. Plug, or ground key, bibbs are not suitable for water which carries fine sand or grit in suspension. The fine particles of sand will get in between the plug and the socket and cut grooves, thus forming small waterways and causing the cock to leak. Neither are they very suitable for high pressure, if much used, because of the unavoidable wear and tear on the parts whose seats have been ground, which under a high pressure will soon leak. They are, however, suitable for low pressure if the water is free from grit.

82. Compression cocks are suitable for faucets only, and should not be used as cut-off or controlling valves.

For faucets, compression bibbs have the advantage over plug cocks of closing slowly, and thus avoiding destructive shocks upon the piping. Also, if they become leaky, they can be readily supplied with a new valve disk; while, if a plug cock becomes leaky, it must be reground.

83. Hot-water connections may be made of lead, brass, copper, or galvanized iron. Plain iron is unsuitable. The choice will depend upon the pressure and upon the appearance desired; also, upon the character of the water, and its action upon the metal. In all cases where the water corrodes the metals named, pipes must be used which have an interior coating of glass or porcelain or are lined with pure block tin.

Brass tubing has these advantages: It will not corrode to any appreciable extent in pure water, and it will not sag in consequence of heat, as lead will do.

For carrying cold water, galvanized-iron pipe is generally used. It will endure the corrosive action of moist earth better than lead.

To secure easy curves and to avoid a multiplicity of sharp turns resulting from the use of elbows, T's, or other iron pipe fittings in a building, the iron supply pipes may be continued to the fixtures with lead pipe which can be easily bent to fit any position.

In cases where it is known that the water will not corrode either lead or brass, the cold water may be conducted through lead pipe, and the hot water through brass.

Lead is unsuitable for underground pipes, because all soils corrode it externally and gradually destroy it.

Ale, beer, and other liquors should be conveyed in block-tin or tin-lined pipes.

84. Lead pipe is very smooth on the inside, and offers the least resistance to the flow of water. It is easily bent to suit any situation, and easy curves are readily made. It is not suited to high pressures because of its small tensile strength.

Lead pipe varies greatly in quality. The pure lead is soft and pliable, and is particularly adapted for waste piping because it will stretch more equally, and will not tear or crack as quickly as a harder and more impure lead would while being worked into bends, etc. The hardness varies according to the kind and quantity of metals mixed with it. A hard, tenacious lead will stand more tensile strain than a softer lead. Therefore, no reliable estimate can be formed of the actual strength of lead pipe. It will bend under pressure without breaking, and is, therefore, desirable for connections to fixtures that are liable to change their position, in consequence of the settling or rocking of the building.

85. Brass and copper tubing are smooth inside, and are made of any thickness. They are best for heavy pressures of 60 pounds per square inch or more. Below that pressure lead may be used.

86. Galvanized-iron pipe is suitable for the heaviest pressures, but it must be put together with screw joints. The short bends and sharp angles, incident to this mode of connection, cause much friction, and impede the flow of water.

87. Plain, or black, wrought-iron pipe is subject to the same drawbacks, and it also rusts rapidly; it is very liable to clog by rusting internally.

88. Soil pipes should be made of cast iron not less than 1/8 inch thick for diameters of 4 inches or less, nor less than 5/32 inch thick for larger sizes.

For buildings under 65 feet in height, the standard grade is sometimes used, but in buildings higher than 65 feet, extra heavy soil pipes should be used. We recommend the exclusive use of extra heavy soil pipe and condemn standard cast-iron soil pipe as being unsuitable for house drainage work.

89. Wrought-iron pipe, put together with screw joints, is coming into use in some quarters, but it is still regarded as problematical. It appears to have some advantages.

When once made tight, it will remain so. The number of joints is much less. In some situations, screwed joints can be made where socket joints cannot be calked.

Wrought-iron pipe is very rigid; it is able to stand upon an independent base, and can thus be detached from the walls of the building. Its expansion and contraction due to changes in temperature is somewhat more than that of cast-iron pipe.

All soil or vent pipes of cast or wrought iron should be coated outside and inside with hot asphaltum. This should be done at the mills, by the maker. The fittings for soil, vent, or drain pipes, of cast or wrought iron, should always be flush fittings, so that the bore of the pipe shall be uniform, without enlargements or pockets.

90. Lead, as a material for soil or drain pipes, is rapidly going out of use. The chief virtue of lead pipe is the smoothness of its interior surface, which enables waste matter to flow through it very easily. Lead pipe will not corrode internally to a serious extent if it be well ventilated. Nearly all varieties of soil or earth will corrode lead pipe externally, therefore, it should not be used for underground drains. It should not be enclosed by cement or mortar where it passes through a wall without first being wrapped with tarred paper or other rot-proof material.

Lead soil pipes should not be less that 1/8 inch thick. Steam rapidly destroys lead soil and waste pipes, and plumbing fixtures using hot water should not discharge into them. The alternation of hot and cold water will cause the lead to crack at the weakest point, usually at the supports.

If steam or very hot liquids are to be admitted to a drain, the pipe should be of wrought iron with screwed joints. The alternate expansion and contraction will strain and eventually destroy the calking in hub and spigot joints of cast-iron pipe.

91. Earthen or vitrified pipes are suitable for underground drains only, and even for that use are inferior to the cast-iron pipes. They should never be used inside of a building, nor in any situation where the leakage from them can do any damage. They should not be used in the neighborhood of wells or cisterns, because they are so liable to crack and leak, and thus pollute the water in the soil for a considerable distance. They should not be laid in new or made ground, as this will settle with heavy rainfalls and the pipes will break. The pipes being so short, the number of joints is greater than of any other kind of pipe. Plain earthen pipes should only be used to drain wet ground. The vitrified or salt-glazed pipe should be chosen to convey sewage.