The Overhaul of Traps in Power Plants

The steam turbine drainage system is an important part of the steam turbine thermal system, especially the steam turbine body, main steam, reheat steam, high and medium pressure valves, feed pump steam turbine new steam drainage and other important drainage valves. When the heating pipe is working, the water can be drained normally in time. When the unit is in normal operation, the valve is required to be reliably isolated without leakage. If these traps leak, the impact on the efficiency of the unit is very obvious. In view of this, some important drain valves are imported valves, which are pneumatic two-position globe valves. The globe valve has the advantages of simple structure, good sealing performance and easy maintenance. The globe valve is equipped with a pneumatic control mechanism, which makes the valve operate quickly, has a sensitive response and can better meet the requirements of the automatic control of the unit.
 
2. The overhaul of steam traps
Since the valve is composed of two parts, that is, the operating mechanism and the valve body, the disassembly is carried out in two steps.
(1) Disassembling the operating mechanism
Remove the compressed air pipe intake joint, solenoid valve, action switch and other peripheral components connected with the pneumatic control mechanism, and place them in a fixed position. Remove the manual operating device of the operating mechanism and place it in a fixed position. Loosen all the spring-loaded bolts on the top of the operating mechanism. Loosen the fastening bolts at the connection between the operating mechanism and the valve stem, and move the fastening ring slightly upwards. Loosen the connecting bolts on the Huff lock block that fixes the operating seat on the valve body, and remove the two lock blocks respectively. Connect the two lock blocks with bolts and place them in a fixed position. Loosen the connecting nut between the valve stem and the operating mechanism with a wrench until the operating mechanism is disconnected from the valve body, and the operating mechanism is placed in a fixed position.
 
(2) Disassembling the valve body
Use an Allen wrench to loosen and remove the fastening bolts on one side of the bonnet. Screw in the fastening bolts from the other side, and place a piece of iron with a thickness of about 1mm and a diameter Ø35 to Ø40 in the middle slot where the bonnet is fastened. Tighten the fastening bolts with an Allen wrench, and further open the slot of the valve bonnet to increase the gap. Use an Allen wrench or rubber clapper to turn or knock the cover, so that the cover rotates counterclockwise until it is unscrewed and removed, and placed in a fixed position. Tap the outside of the packing gland with a red copper rod until it is loose, and then take out the packing gland. Take out the door rod and door core, and place them in a fixed position.
 
(3) Inspection
After the valve is completely disassembled, the sealing surface and other parts of the valve should be inspected. Inspection for the valve seat and valve spool: The valve line seal should be in full contact, and there should be no defects such as grooves and blow damage that affects the seal. The sealing surfaces between the valve stem, valve casing and packing gland should be in good contact. The inlet and outlet of the valve should be free of foreign matters and impurities.
 
(4) Maintenance
If the valve line is damaged by blowing, the valve line in the valve core and valve seat should be treated differently. The valve line on the valve core should be turned on the lathe at the original angle; the cemented carbide sealing surface in the valve seat should be removed by dedicated tools. The amount of the sealing surface removed is about 0.05 to 0.08mm each time, which is determined according to the actual situation of the defect of the valve. After observing that the sealing surface is free of dents, finely grind the valve with abrasive paste. After the valve is ground, evenly apply blue oil or red lead to the sealing surface of the valve core; fix it with a special sleeve, and send it to the valve seat for sealing contact test. The sealing surface should be in uniform and uninterrupted contact around the entire circumference.
 
If the packing in the stuffing box is non-flexible graphite packing, it should be replaced with flexible graphite packing. The original flexible graphite packing should be checked for damage. If it is damaged, it should be renewed. The sealing surface on the valve stem (the part being in contact with the packing) should be bright and free of rust, and the self-sealing surface in the valve seat and the lower part of the stuffing box should be polished. The surface of the connecting thread on the top of the valve stem should be clean and the connection should be flexible. The threaded connection of the packing compression sleeve should be cleaned so that it can move freely, ensuring easy adjustment during the normal operation of the unit.
 

(5) Installation

After the cleaning and inspection are performed, all the connecting threads should be coated with anti-seize paint, and then the valve can be reassembled. Reassembly should be carried out in the reverse order of the disassembly procedure.
 
(6) Adjustments and matters needing attention
After the operating mechanism is connected with the valve stem, the lower limit of the valve (the close direction) is adjusted at the beginning. When the valve stem thread is screwed into the connecting nut of the operating mechanism, connect the compressed air directly to the air inlet of the operating mechanism; open and close the valve, and adjust the connecting nut until the valve is fully closed at the connection between the operating seat and the valve body. Leave a gap of 3 to 5 mm at the bottom. The preliminary adjustment is over. The Huff lock block is not installed at this time.
 
Open the valve by pneumatic control. After the control seat frame is tightly connected with the valve body, install the Hada lock block and tighten the fastening bolts. Pneumatic control makes the valve open and close. Adjust the opening indicator of the valve so that the position of the pointer of the valve matches the actual opening and closing position of the valve. After the solenoid valve, action switch and other peripheral equipment are installed, adjust and verify the switch signal indication together with the thermal control professional to confirm that the opening and closing directions are correct, and the adjustment is completed.