The position in which the safety valve is on the primary return is generally considered as good as any. There is no doubt, however, that theoretically the ideal place for a safety valve is directly in the boiler, which is the seat of danger; but this position is seldom available, and at best the valve would be out of sight, and this is not desirable. The valve is therefore connected to the boiler by a pipe that will not readily become stopped up. The flow pipe is the least desirable position, as in hard-water districts the pipe is apt to choke with deposit. The return pipe is much less liable to choke. Perhaps the best way is to connect to the boiler by an independent 1-in. pipe, screwing this through the top of the boiler so that it projects down about lin. inside. It is not likely to be shelled over or stopped with lime deposit if done in this way.