GLASS STRUCTURES AND APPLIANCES. 



275 



The india-rubber rings make excellent joints 

 (Fig. 48, in which, a shows the ring before, and h 

 after, the joint is made). They require very little 

 skill, are made quickly, and can be taken to pieces, 

 and removed or altered in a very short time. Cement 

 joints take up less space, they locl^ neater than 

 screws, and their cost when fixed is abuut the same ; 



but if alterations or 

 removal are neces- 

 sary they become 

 more expensive. 



Fig. 43.— Ring Joint. 



Pig. 49.— Flange Joint. 



Fig. 50. — Ordinary Throttle-valve. 



Iron cements re- 

 quire skilful pre- 

 paration, as o\sdng 

 to the chemical 

 change which even- 

 tually sets in, 

 tightly - caulked 

 joints often burst 

 the sockets. When 

 spigot and faucet 

 pipes are used, red 

 and white lead, 

 thoroughly mixed, 

 and strands of tar- 

 red hawser - rope, 

 make joints equal, 

 and in many re- 

 spects superior, to 

 the best mineral 

 cements. By the 

 application of fire 

 these joints can be 

 fused and taken to 

 pieces without 

 breakage. An ex- 

 cellent joint can be 

 made by caulking 

 with rope, and 

 facing with Port- 

 land cement ; but, 

 like the joints made 

 with iron filings 

 and sal-ammoniac, 

 it is almost im- 

 possible to disconnect them when once they are 

 thoroughly set without breaking the pipes. 



Another joint (Fig. 49), which is now rapidly 

 gaining favour, is made with socketless pipes, which 

 butt together, and are kejjt perfectly water-tight by 

 means of vulcanised india-rubber rings, drawn to- 

 gether by two- flanges, which can be tightened with 

 screws and nuts. The pipes being east without 

 sockets, alterations or additions can be quickly made 

 by' unskilled workmen, and any length can be re- 

 moved and replaced with little trouble. 



Fig. 51. 



-Patent Slot Throttle- 

 valve. 



Valves.— Without vtdves a complicated heating 

 apparatus would be like a ship without a rudder. 

 The circulation in a single flow and return pipe, like 

 that shown in Fig. 47, can be regulated by stopping 

 or increasing the fire ; but when more than one series 

 of pipes is used, stop-valves become absolutely neces- 

 sary. The ordinary throttle- valve (Fig, 50) is made 

 with a metal disc, which offers very little resistance 

 to the water when onen. TMien closed it checks the 



Fig. 52. — Improved Diaphragm Valve. Section. 



Fig. 53.— Improved Angle Valve. Section. 



Fig. 54. — Improved Slide Valv.e. 



Section, 



circulation fairly well, but the discs being made of 

 brass, and the body of the valve of cast iron, they 

 soon get out of order. Valves should always be 

 placed in returns, as well as in flows, otherwise, espe- 

 cially when boilers are shallow, and the orifices of 

 the flows and returns are near to each other, the 

 water will circulate backwards, it will leave the 

 boiler by the return-pipe, and return by the flow. 



The slot throttle-valve (Fig. 51) is a great improve- 

 ment on the old throttle-valve. 



