ARRANGING AND FIXING HOT- WATER PIPES. 



253 



It is considered that a continuous rise of one inch in seventy-two inches is neces- 

 sary to secure a good circulation of water in the apparatus. If "dips" cannot be 

 avoided a competent engineer ought to be employed to make the necessary arrange- 

 ments for obviating the difficulty, as this will be found economical in the end ; also 

 avoid employing small pipes to connect the principal pipes in the houses witli the boiler, 

 as these check free circulation ; and it may be pointed out that pipes exposed in and 

 about the stokehole, or any forming the mains, ought to be well enclosed with felting 

 or asbestos for preventing waste of heat. 



Joints. — The joints of pipes near the boiler are usually " made " with rope and 

 either red lead or iron filings, mixed with ammonia to hasten rusting and insure solidity. 

 For other positions expansion joints are now preferred, as these are more easily put to- 

 gether and can be taken apart as often as may be needed. Pipes are specially cast for 

 the purpose, some with and others without socket ends; loose glands or collars, enclosing 

 india-rubber rings and bolted together, form a perfect expansion joint. The fittings 

 are supplied to correspond, and an ordinary workman can put all together. 



Supply Cisterns. — These are necessary for keeping the pipes filled with water, and 

 they also answer the purpose of expansion tanks. Wherever located they must be 

 fixed a little above the level of that of the highest pipes they have to supply. In the case 

 of a very small apparatus, the cistern is often fixed at the end farthest from the boiler, but 

 for all large and moderately large apparatus, the cisterns are usually fixed nearly over 

 the boiler, and the feed pipe connected with a return pipe near to where it enters the 

 boiler, the coldest water thus being brought nearest the fire. 



Air Pipes. — At the extreme ends of each section of flow pipes, and at the points of 

 their greatest elevation, outlets are needed for the air that has to escape before the pipes 

 can be filled with water. At these and other raised bends the air is apt to collect, 

 and impede the circulation of heated water, and therefore pipes or taps must be pro- 

 vided for the exit of the air. If taps are used they ought to be opened frequently, a 

 very little air effectively stopping the circulation; while if lead pipes are preferred, 

 these must terminate 3 feet higher than the feed cistern, and should be examined 

 at least every autumn to see that the apertures are not stopped up in any way. 



Valves. — If only one house is heated by a boiler, valves can be dispensed with, 

 though they are often serviceable ; but they are absolutely necessary where several 

 houses or divisions have to be heated from one boiler. By their aid the heat can be 

 regulated as desired, checking the hot water from unduly rushing to certain points, and 



