When defects appear on the sealing surfaces of valve heads and valve seats, if the defect depth is less than 0.5mm for valves without being nitrided, abrasive machining shall be done directly to eliminate the defects or the method of lathe machining before abrasive machining shall be adopted, which depends on the damage condition of the sealing surfaces. If the surface of the valve is nitrided, the valve should be nitrided again after eliminating the defects on the sealing surface of the valve head and the valve seat.
When the defect depth on the sealing surface of valve heads and valve seats exceeds 0.5mm, surfacing should be performed first, then lathe machining and abrasive machining should be done in turn to meet the quality requirements of the valve. Assemble the new valve; remove the old one; clean the sealing surfaces of the two flanges of the mouth of the pipe; brush with lead powder oil; finally put the new valve in place; install gaskets; symmetrically tighten the flange and fasten bolts.
For welded valves, the new valve should be disassembled and inspected before replacement. If it is an alloy valve, the materials of all parts of the valve should be tested and verified, and all the materials should be qualified. Cut off the old valve; repair the groove of the two mouths of the pipe; weld the valve seat of the new valve in place. The alloy valve should be preheated before welding and heat treatment should be done after welding. After the ultrasonic inspection and hardness testing of the weld are qualified, replace the seal and assemble the new valve.
When the defect depth on the sealing surface of valve heads and valve seats exceeds 0.5mm, surfacing should be performed first, then lathe machining and abrasive machining should be done in turn to meet the quality requirements of the valve. Assemble the new valve; remove the old one; clean the sealing surfaces of the two flanges of the mouth of the pipe; brush with lead powder oil; finally put the new valve in place; install gaskets; symmetrically tighten the flange and fasten bolts.
For welded valves, the new valve should be disassembled and inspected before replacement. If it is an alloy valve, the materials of all parts of the valve should be tested and verified, and all the materials should be qualified. Cut off the old valve; repair the groove of the two mouths of the pipe; weld the valve seat of the new valve in place. The alloy valve should be preheated before welding and heat treatment should be done after welding. After the ultrasonic inspection and hardness testing of the weld are qualified, replace the seal and assemble the new valve.
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