BOILERS AND PIPES. 



245 



at the junction of three sets of double 

 pipes— one on each side of a high-pressure 

 boiler ; and they allow the water to flow, 

 or check it, as may be required. When 



the part of the stopper marked g on the 

 cross section is in the position shown in 

 the fig., the cock is open in every direc- 

 tion, allowing the water to flow freely 



Fig. 323. 



from the boiler along the pipe a, and 

 through the cock into b and c, returning 

 again by e and / in the under part of the 

 cock, and into the under part of the boiler 

 by the main return d. When g is turned 

 round in front of pipe b, no circulation 

 takes place in that direction ; the whole 

 water then flows along the pipe c, and re- 

 turns by the under part of the cock /, 

 and into the boiler by d. When g is 

 placed in front of c, the flow and return 

 is there stopped, and the water flows and 

 returns by b and e into the cock, and into 

 the under part of the boiler by d, as indi- 

 cated by the arrows shown on section. 

 And again, when g is placed in front of 

 all connection with the cock is cut off, 

 and the water from the boiler flows along 

 the other set of pipes situated on the left 

 hand of the boiler, which can, in this 

 case, be more quickly heated if required. 

 These cocks are made for 4-inch pipes, 

 and are bored, turned, and ground very 

 exactly, to prevent any heating from the 

 different branches. They are solid in the 

 bottom, which prevents leaking, and have 

 a close cover ground into the outer case, 

 and on to the top of the movable stopper. 



Some of these stopcocks are made to 

 circulate along a, and return down through 

 the stopper to the boiler by d, without 

 going into any of the other branches. 

 These latter have not the branches b or e. 



Stopcocks are both an expensive, and 

 often an unsatisfactory part of a heating 

 apparatus. One of the simplest substi- 

 tutes is thus described by Tomlinson, and 



may be made applicable where two or 

 more hothouses are to be heated by the 

 same boiler, or where bottom and atmo- 

 spheric heat is supplied from the same 

 source : " To effect this, a small open 

 cistern, a, should be placed on top of the 

 boiler b, as shown at fig. 324, and from 

 the bottom of this cistern the various 



Fig. 324. 



flow-pipes are made to branch off. By 

 this means," he says, "the expense of 

 stopcocks or valves is avoided ; for by 

 driving a wooden plug into one or more 

 of the pipes which open into the cistern, 

 the circulation will be stopped until the 

 apparatus is heated j — but in that case, 

 water will flow back through the return- 

 pipe. This, however, may be prevented, 

 by bending a lower portion of the return- 

 pipe into the form of an inverted siphon, 

 as shown in the figure. This will not 

 prevent the circulation when the flow- 

 pipe is open ; but if that be closed by a 

 plug in the cistern, the hot water will not 

 return back through the lower pipe. Any 

 sediment that may accumulate in the 



