HIGH-PRESSURE TEST.

Waikato Times, Volume 117, Issue 19596, 7 June 1935, Page 7

HIGH-PRESSURE TEST.

TELEGRAPH LINE INSULATORS. POST OFFICE PURCHASES. Pressures up t’O 2500 lb. to the | square inch are applied by the Post Office engineers in the testing of insulators for New Zealand’s telephone and telegraph lines. These familiar objects perform a very important function in connection with the electric circuits which cover the Dominion, and they must be efficient Before any types of insulators are taken Into -service, samples are submitted to rigorous tests by the chief engineer’s technical staff. A porous insulator permits electric current to leak and must not be employed on a line; therefore ono of 'the important tests is to ascertain the degree of porosity in ihe insulator. It is placed in a steel i chamber resembling a bomb partly filled with vermillion dye. The pressure of the liquid is raised lo 2500 lb. while the insulator is in the chamber and it is afterwards cracked for examination. If any of the tell-tale dye has been squeezed into the body o i' the insulator it fails to pass the test. Weathering properties are also important. and on a lofty building scores of insulators of different designs and material, including glass, are kept under ordinary service conditions for long periods and regularly tested to ■ ascertain whether they are maintaining their efficiency as non-conductors. 1 The roof is frequently swept by heavy gales carrying salt-spray, a very thor- ■ ough test of their weather resisting qualities. ' ' Tim Post Office has purchased 1 155,000 insulators during the past five '■ years.