Water Pressure.—Pressure at a fixture or outlet so that the water will flow is generally obtained by the force of gravity. When this method is not sufficient, a pneumatic system is employed. This method is employed to force the water to the top floors or to supply the whole building in high structures. The pneumatic system requires a pump, an air-tight tank, and pipes to the various outlets. The water pumped into the air-tight tank will occupy part of the space generally occupied by the air. The air cannot escape and is, therefore, compressed. Continued pumping will compress the air until the limit of the apparatus is reached. If a valve or faucet that is connected with the tank is opened, the air will expand and force the water out of the opening. This explains in a general way the operation of a pneumatic water-supply system. Water can be pumped into this air-tight tank from a well, cistern, river, lake, or from the city supply mains.
Piping.—From the service pipe on which there has been placed a shut-off, a line of piping, full size, is run through the basement, overhead to a convenient place, perhaps to a partition in the center of the cellar. The pipe is brought down and connected into the end of a header. This header or banjo is made of Ts placed 4 inches center to center. From each T a line of pipe is run to each isolated fixture or set of fixtures (see [Fig. 70]). A stop and waste cock is placed on each line at such a point that all stop cocks will come in a row near the header. A small pipe is run from the waste of each stop and discharged into a larger pipe which connects with a sink. This way of running pipes while it is expensive makes a very neat and good job. Each stop cock has a tag on it stating explicitly what it controls. If the building is a large one a number of these panelled headers are used. A less expensive way to run this pipe is to branch off from the main at points where the branch pipe will be as short as possible and use as few fittings as possible. Stop and waste cocks are then placed on each branch near the main.
All pipe must follow the direct line of fitting with which it is connected. The line of pipe should be perfectly straight. If it seems necessary to bend the pipe to get around an obstacle, then good judgment has not been used in placing the fitting into which the pipe is screwed. The fitting should be re-located so that the pipe can be run without bending. To have true alignment of pipes the whole job or section of the job must be drawn out on paper first and any obstacles noted and avoided before the piping is cut. This not only saves time but it is also the forerunner of a good job. When getting measurements for piping the same rule or tape should be used to get out the pipe as was used to get the measurements.
The water main and branches that run through the basement of a building are generally hung on the ceiling. Rough hangers of wood, rope, or wire are usually used to hold the pipe in place at first, then neat and strong adjustable hangers are placed every 8 feet apart. There are in use too many kinds of hangers to explain or describe them here. The essential point of all good hangers is to have them strong, neat, and so made that perfect alignment of the pipe can be had. The hangers should be so placed that no strain will come on the fitting or the valves. A hanger should be placed near each side of unions so that when the union is taken apart neither side of the pipe will drop and bend. Hooks and straps should be used to hold vertical pipes rigid and in position. A vertical pipe should be so held in place that its weight will come on the hooks and straps that hold it rather than on the horizontal pipe into which it connects. Where there are six or eight horizontal lines of pipes close together, a separate hanger for each pipe makes a rather cumbersome job and it consumes considerable time to install them properly. A hanger having one support run under all the pipes will allow space for proper alignment and adjustment for drainage. Allowance must be made on all lines of pipe for drainage. When a building is vacant during cold weather, the water is drawn off; therefore, the pipes should have a pitch to certain points where the pipes can be opened and the entire system drained of water.
Kinds of Pipe.—The kind of pipe that is used for cold-water supply depends on and varies according to the kind of water, the kind of earth through which it runs, and the construction of the building. Wrought iron, steel, lead, brass, tin-lined brass, are in use.
The supply pipe to every fixture should have a stop on it directly under the fixture. This will allow the water to be shut off for repairs to the faucet without stopping the supply of other fixtures.
The making of perfect threads on pipe is an important matter, especially on water pipes. If the pipe and the dies were perfect, and the mechanic used sufficient oil in cutting, and the fittings were perfectly tapped to correspond to the dies used on the pipe, of course a perfect union between pipe and fitting would result and the joint would be found to be perfect on screwing the pipe home. As all the above conditions are not found on the job, threads are made tight by the use of red or white lead and oil. The lead is put on the thread and when the thread is made up the lead will have been forced into any imperfection that may be in the threads and the joint will then be water-tight. White lead and oil should be used on nickel-plated pipe as other pipe compounds are too conspicuous and look badly. A pipe compound should be used with discretion, for if too much is put on a burr of it will collect in the bore of the pipe and reduce it considerably. This is not tolerated, so only a small amount is used. Water pipes should be run in accessible places, making it possible to get at them in case of trouble. In climates that have freezing weather water pipes should not be run in outside partitions. If it is found absolutely necessary to do so, as in the case of buildings which have no inside partitions on the first floor, the pipe should be properly covered and protected. The different methods of covering pipes are described in [Chapter XV].