264 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1957 



the special quick-release clamp used for handling the repeater during 

 the laying operation. 



Protection against corrosion is provided by shot-blasting the surface 

 and then applying hot-sprayed zinc to a thickness of 0.010 in, followed 

 by two coats of \'inyl paint. The A-end of the repeater is finished red. 

 The dimensions of the complete repeater are 8 feet llf inches X lOJ 

 inches diameter, and its weight is 1,150 lb in air 



Sealing of Housing 



The bulkheads, which register on seatings designed to withstand the 

 axial thrust due to the water pressure, are in the form of discs with ex- 

 tended skirts. A watertight and diffusion-proof seal is formed between 

 the casing and the outer skirt of each bulkhead by a silver-soldering 

 process, using carefully controlled electromagnetic induction heating to 

 raise the jointing region to the required temperature. The diametral 

 clearance between the cylinder and the locating surface of the bulkhead 

 is 0.003 inch ± 0.002 inch, the diameter of the bulkhead being reduced 

 b}' 0.004 inch for an axial distance of 3 inches from the rim of the skirt 

 to provide a recess into which the molten solder can flow. 



The solder is applied as eight pre-formed No. 16 s.w.g. wire rings which 

 are fitted into place cold and coated with a paste formed by mixing flux 

 powder with dehydrated ethyl alcohol. The generator used for heating 

 has a nominal output of 50 kw at a frequency of about 350 kc and is 

 capable of raising the temperature of the jointing region to 750°C in 5 

 min. The temperature, as indicated by four thermocouples inserted in 

 special holes drilled in the ends of the casing, is maintained at 750°C for 

 a period of 45 min to allow ample time for the entrapped gas and flux 

 pockets to float to the surface. Fig. 9 shows the arrangement for solder- 

 ing in a bulkhead. 



The primary object of the outer skirt is to keep the heated region far 

 enough away from the base to prevent the temperature of the latter rising 

 unduly. Temporary water jackets are also clamped o\'er the gland and 

 around the outside of the casing during the sealing operation. A sub- 

 sidiary skirt on each bulkhead contains a vent hole which serves to allow 

 displaced air to escape as the bulkheads are inserted into the casing. 

 These vents are later used to apply a low-pressure gas-leak test to the 

 bulkhead seals and then to flush the housing with dry nitrogen to remove 

 any trapped moisture. The vents are finally sealed. At this stage the 

 sealed housing is pressure-tested in water at 1\ tons*/square inch for a 



* These are long tons. 1 long ton = 2240 lb. 



