A Watched Valve Never Boils

CCI Sweden (formerly BTG Valves) instructed Wieslaw Konieczny, the Inspector for Maintenance and Repair at the Zespót Elektrocieplowni Pozananskich power plant in Poznan, Poland, “not to open the two VFA boiler feedwater valves for five years.”

“We haven’t touched them either,” says Mr. Konieczny, “because during the four years since 1995, when they were installed, they have shown absolutely no sign of leakage. And unless the valves are unintentionally damaged by foreign particles entering them…we expect to find no sign of cavitation. So all we expect to do after inspection is change the packaging in the special seal bonnet.”

Wieslaw Koniezcny, the Inspector for Maintenance and Repair at the Zespót Elektrocieplowni Pozananskich power plant.

“No cavitation in 10 years would be ideal,” adds Mr. Konieczny.

At the Poznan power plant, a single line fitted with a feedwater pump feeds high-pressure steam to two boilers. The two VFA feedwater valves are positioned between the pump and a shutoff valve in each of the lines into the boilers. These valves are designed to resist cavitation damage at extreme pressure differences of short duration.

Mr. Konieczny explains, “We use the feedwater valves in both startup and normal operations. Starting both boilers at the same time presents no problem because the level of high-pressure water coming from the feedwater pump can be divided between the two feedwater valves.”

“However,” Mr. Konieczny adds, “starting up one boiler while the other is in operation is more problematic because the feedwater valve has to cope with the full pressure required to keep the other boiler in operation.”

Under these circumstances, the valve has to be able to handle extreme turndown ratios. For example, water can enter the valve at approximately 2470 psi (170 bar) and exit at 73 psi (5 bar), and if it is not well designed there is great risk of cavitation, a costly problem.

“A gap caused by cavitation of only .08-in. (2-mm) between the valve body and the seal under these circumstances can mean a loss of 30 tons of water per hour,” says Mr. Konieczny.

To date, apart from these two VFA valves, there is one other CCI Sweden valve at the Poznan plant, a VLB turbine bypass valve.

Mr. Konieczny concludes, “In the future we hope that all of our steam conditioning equipment can be from CCI Sweden.”

Published in SOLUTIONS Fall 2002