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 this expansion, and on the first floor they were connected as in Figure 33. If the radiator connections were very short, two joints would have been put on each of these risers.

In laying out large systems, valves should be placed on each riser so that each one can be shut off independently of the others in case of leaks or in case of repairs or changes to be made on any of the radiators. Gate valves should be used preferably on account of the fact that they interpose infinitely less resistance to the flow of steam or water than do globe valves. Furthermore, in such cases provision should be made for changes in the arrange- ment of rooms and consequent changes in the location of radiators. It is a very good practice to put tees on each riser at each floor whether or not, in the first instance, a radiator connection is re- quired, as subsequent changes in the arrangement of rooms may make it desirable to change the radiators.

Figure 36 shows the arrangement of piping in the attic of the Ellicott Square, a large 10-story building in Buffalo, N. Y., which is heated by direct radiation on the overhead system. The figure illustrates the method of connecting the overhead mains to the risers, and also the way in which expansion of the mains is pro- Tided for by bends and offsets. In this instance the piping was rigidly anchored at four points marked D, and the expansion al- lowed in all directions from these four points. It may be noted here that branch mains were taken off at points marked E and F, instead of connecting each riser to the main 10-inch pipe at these points. This was done for the purpose of saving the expense and 'the delay to the work of connecting each riser into the 10-inch pipe.

Valves. Much care should be used in placing valves on a piping system. Gate valves should always be used on mains. If globe valves are used anywhere, the stems must be placed horizontally, as otherwise they form a water pocket. Thermostatic valves, so- called, are often used on radiators, being connected with an auto- matic device which opens the valve when the temperature falls, -and closes when it rises.

Location of risers. In laying out the floor plans for the heating system of a large office building it is a mistake to try to reduce the number of risers to a minimum. It is much better to put in risers enough so that a radiator can be placed under any window in the building without too long a connection from the riser, for