James Walker first investigated ED when trouble-shooting problems in oilfield equipment. At that stage, little was known of the ED mechanism, only that ‘O’ rings failed when gas pressure suddenly dropped from high to low.
Tests showed that high-pressure gas permeated elastomeric seals over time. The seals operated efficiently so long as the gas inside them remained in equilibrium with ambient pressure. But when external gas pressure was suddenly removed, the gas inside the seal cracked and blistered the elastomer as it rapidly expanded and escaped.
Until the phenomenon was fully understood, the solution was to use the smallest diameter section that did not compromise sealing efficiency, and to constrain rings more tightly in their housings. There was less seal surface for high-pressure gas to permeate, and the seal could not expand beyond its mechanical limits when external gas pressure dropped.
However, the real solution was achieved after extensive research into ED mechanisms and James Walker’s development of special ED-resistant elastomers to work in aggressive media at high pressures and extreme temperatures.
James Walker produces five ‘flagship’ grades of ED-resistant elastomer that have been extensively validated for ‘O’ rings and other seals. Many of the seven million ‘O’ rings it stocks to international standards are now ED-resistant.
James Walker & Co Ltd is based in Woking, Surrey, UK. www.jameswalker.biz
