Several power plants worldwide are equipped with a gas turbine installation from the manufacturer named Mitsubishi Heavy Industries Japan. Mitsubishi is working closely with the company Nakakita Seishokushio who is the world leading manufacturer of control, butterfly safety valves, and automatic controllers. Due to this relationship, all the power plants that are built by Mitsubishi, are equipped with Nakakita valves.
Earlier last year a major Dutch power plant contacted Ravebo with a problem concerning an emergency shutdown gas valve. They requested our service as Ravebo is the European sales and service agent for Nakakita. Upon investigation, the problem was identified when closing the valve as this was not lowering smoothly but with a juddering movement. The replacement packing’s were arranged via Nakakita who were able to deliver within a very short time and with these spares 2 service engineers attended the power plant to overhaul this special valve. After they opened the valve the conclusion was that the gland packing was the problem and was replaced by a new set.
Other packing’s were replaced as well and the valve was re-assembled accordingly and the operation test could be started. The first test (opening and closing) was made successfully in a non pressured situation. The second test was made under a pressure of 5 bar with Nitrogen and was closing/opening correctly. During this test, the valve was checked if it was gastight and no leakage was observed. The last test was made in a operational situation with 40 bar gas in the line but the valve was opening and closing without any problem. Again the valve was checked if it was gastight and passed the survey without any problem and was in a very good working condition.
Later on that year 2 other valves from 2 other units were overhauled successfully as well.