266 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1957 



Fig. 10 — Section of high-pressure gland. 



bulkhead, and the initial seal is formed by the contraction, during cool- 

 ing, of potythene moulded on to the core and enclosing a steel stem, hav- 

 ing a castellated profile, which forms part of the bulkhead. Each side of 

 the castellation has a taper of about 7°. The application of water pressure 

 increases the contact pressure between the polythene and the stem, thus 

 making the gland inherently self -sealing. As an additional safeguard, the 

 gland stem is first prepared by a lead plating and anodizing process, 

 followed by the application of a thin film of polythene which forms a 

 chemical bond to the plated surface. The injected polythene merges with 

 this film, thus bonding the molded portion to the castellated stem. Tests 

 on sample gands, using a radioactive tracer, have shown no measurable 

 (less than 0.001 mg) water diffusion at a pressure of 5 tons*/square 

 inch over a period of 6 months. 



Intrusion of the potythene into the housing, at hydraulic pressures up 

 to at least 6 tons*/square inch, is eliminated by the use of a small-diame- 

 ter core and by the provision of a screw thread in the hole through which 

 the core passes. During the molding operation a corresponding thread is 

 formed on the polj^thene core itself. This method of construction dis- 

 tributes the axial force over a sufficiently wide area to prevent any ap- 

 preciable creep of the polythene. 



