AIR COMPRESSORS 97 



faster (or longer) and against a higher pressure, either of which 

 tends to cause overheating. A much higher pressure is required 

 in the main reservoir than in the brake pipe, not only to 

 release brakes, but also to force the air through the brake pipe 

 in the shortest time possible and thus release all brakes on a 

 long train promptly and as nearly simultaneous as possible. 

 About 20 Ib. more pressure in the reservoir than in the brake 

 pipe is usually needed with a large reservoir; with a small 

 reservoir, more than 20 Ib. is necessary. In ordering main 

 reservoirs, the pressure, outside diameter, and length over 

 all, in inches, and any special features, such as special pipe 

 tapping, handholes, etc., must always be given. 



Styles of Reservoirs. Main reservoirs are made in three 

 styles: The shell of drawn tubing with convex heads welded 



in; the shell of drawn tubing with semiconvex heads welded 

 in; the shell riveted with semiconvex heads welded in. Also, 

 reservoirs are made with brazed seams for shell and heads. 



Standard Tapping. The standard method of tapping main 

 reservoirs is shown in the accompanying figure. Pipe tap B is 

 central, and there is one tap in each head. If there are two 

 tap holes in the same reservoir head, they must not be closer 

 than 4 in. between centers. Also, no hole should be placed 

 closer to the shell than 5 in. from the center of the hole to 

 the shell of the reservoir. The proper size of pipe taps for the 

 different size reservoirs is given in the table showing the style 

 of construction. 



Enameled Reservoirs. Reservoirs enameled by special 

 process are recommended on account of their durability 

 and because both inside and outside surfaces are protected 

 against corrosion, oxidation, etc., thereby preserving the 

 initial factor of safety. The reservoir is thoroughly cleaned 

 in an acid bath, neutralized by an alkali, and carefully washed 

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