Leverless limit switches halt downtime at Avon Lake

Issue 4 and Volume 99.

Leverless limit switches halt downtime at Avon Lake

Repeated limit switch failures, costly maintenance and downtime spurred Cleveland Electric Illuminating Co. to consider upgrading and expanding the water treatment plant at its Avon Lake Generating Station Unit 9. The water facilities package was broken into segments supplied by different manufacturers, with the pretreatment system, demineralizer system and condensate polishing system all under scrutiny as the company studied alternatives for the upgrade.

As originally supplied, the associated valving incorporated mechanical limit switches with lever arms, lever shafts and enclosures with gaskets. The limit switches are tied into control systems and show open and/or closed positions of valves. In some cases they indicate whether the water treatment at various stages of the process meets the station criteria for the water used in the boiler. Unless the limit switches are being tripped, the computer will not allow the process to continue until the fault has been corrected.

Limit switches supplied as original equipment in this application had a high failure rate, attributed to the harsh environment, which included moisture ingression, chemicals such as caustic solutions and sulfuric acid, and flyash. The areas at Avon Lake Unit 9 causing the greatest problems were the makeup system, condensate prefilters, condensate demineralizers and the demineralizer regeneration system. The boiler operates at high temperatures and pressures and requires stringent control to maintain the water treatment process.

Cleveland installed OleverlessO limit switches and valve indication packages from GO? Switch designed for harsh conditions. The switches are fully encased in stainless steel and are factory-wired with a quick disconnect. GO Switch supplied 73 Series GO Switches and a GO Valve Indication Bracket package custom designed for each valve.

The switches are environmentally sealed in stainless steel or brass housings to withstand temperatures from -40 F to +445 F. They are certified to handle explosion-proof application in Class I Division I and Class I Division II areas as well.

The switches immediately solved the maintenance and control problems at Avon Lake station. They have been maintenance and failure free since installation in 1991 on all water system valves in Unit 9.