Brief introduction of various types of valve maintenance

Valves are one of the indispensable elements in industrial production. However, the types of valves are also various, and the methods of maintenance are also different. Next, we will talk about how to carry out some common valves. Daily maintenance.
First, the extraction check valve
Check valves are valves used to prevent backflow of media in pipes and equipment. The steam extraction check valve is arranged on each of the extraction pipes of the external heater of the steam extraction and regenerative system in the steam turbine unit. The function of the valve is automatically closed when the unit is under load, preventing the steam side of the heater and the steam inlet pipe. Steam is returned to the turbine, causing the turbine to overspeed to avoid accidents.
The extraction check valve of the imported 300MW unit is a gas-controlled swing-type check valve. The structure is shown in the figure, and the structural diagram of the air control seat is shown in the figure. Mainly composed of valve body, valve plate, shaft, bushing, etc., the air control seat is composed of piston, cylinder block, door rod and spring.
The extraction check valve is closed when the unit is started. When the heaters of each stage are randomly started, the air control seat of the extraction check valve is inflated, the piston rod drives the rocker arm to rotate, and the check valve sleeve is facing the valve. The limit of the plate shaft is opened, and the valve plate is in the ** state, the valve plate is opened by the suction pipe pressure, and the steam enters the heater through the valve.
During normal operation of the unit, the check valve plate remains in the normally open position due to the effect of the extraction pressure. When the unit is under load and shutdown, the extraction pressure drops suddenly, and the valve plate quickly returns to its seat by its own weight, closing the valve, thereby preventing the steam in the heater and the pipeline from flowing back into the steam turbine to achieve the protection function.
The preparation work before the inspection of the extraction check valve has the following contents:
After the equipment is out of service, protection and power supply and air supply are cut off, the air intake and outlet connections of the air control seat are released, the pin connecting the piston rod of the control seat and the check valve lever is removed, and the seat of the control seat is released. After fixing the bolts, remove the control seat and place it in a quantitative manner. Then, do the following work.
1, the valve disintegration
(1) First, mark the mating head and the valve body with a marker, and then loosen the cap bolt to remove the cap.
(2) Remove the bearing, the oil retaining ring and the lever on the side of the lever shaft and the air control seat, and set it in a fixed position.
(3) Loosen the large seal nut and remove the large pressure ring.
(4) After making the matching mark, loosen the large bracket fixing bolt, remove the large bracket, and place it.
(5) Remove the lever shaft and bushing and set it in a fixed position.
(6) Remove the small bracket and accessories of the rocker shaft side, and place them in a fixed position.
(7) Loosen the fixing nut on the small pressure ring, remove the small pressure ring, and place it quantitatively.
(8) After making the matching mark, loosen the fixing bolt on the flange cover, remove the flange cover, and place it.
(9) Remove the rocker arm and the valve core, and place them in a fixed position.
(10) Take out the rocker arm and the valve core, and place them in a fixed position.
2, the valve cleaning inspection
(1) Check the valve wire on the valve core and the valve body. There should be no grooves, air holes and traces across the sealing surface that affect the sealing performance. The contact should be uninterrupted throughout the week. If it is found that defects affecting the sealing performance, it should be treated by grinding.
(2) Check the connection between the valve butterfly and the rocker arm. Adjust the gap between the gasket and the rocker arm to be between 1 and 1.2 mm. It should not be too large or too small. Otherwise, adjustment should be made. The connection between the valve butterfly and the rocker arm should be firm. The welded joint should be complete and free of cracks. The gap between the valve shaft and the rocker arm should meet the requirements.
(3) Check that the clearance between the lever shaft, the rocker shaft and the size bushing and the sowing arm should meet the requirements. The surface of each shaft and the inner wall surface of the bushing should be smooth and free of pits.
(4) Check the packing inside the large sealing cover and the flange cover, it should be complete, if it is damaged, it should be replaced.
(5) Check that the sealing surface of the valve cover and the valve body should be complete, and there are no grooves, sand holes and scratches that affect the sealing effect.
(6) Clean the sealing surface of the joint of the inspection bracket, the flange cover and the valve shell, and the old gasket adhered on the sealing surface should be cleaned and shoveled. The sealing surface shall have no defects affecting the sealing effect.
(7) All keys and keyways should be cleaned and the connection should be good.
3, the valve repair
Before the valve is installed, the surface of each shaft and bushing is rubbed with molybdenum disulfide powder to brighten it. The restoration should be carried out according to the reverse step of disassembly according to the assembly mark. The following points should be noted during the restoration process:
(1) After the valve butterfly is connected with the rocker arm, the thickness of the adjusting gasket can be adjusted to ensure that the angle of the butterfly butterfly switch reaches the angle required by the manufacturer. After that, the tightening nut should be welded to the valve butterfly.
(2) When the lever shaft, the rocker arm shaft and the rocker arm are assembled, the adjusting washer and the rocker arm end of the lever shaft, the rocker arm end and the rocker arm shaft should have a gap of 1 to 1.20 mm.
(3) When the bracket and the flange cover connected to the valve shell on the outside of the rocker shaft and the lever shaft are tightened, it is necessary to keep the two shafts concentric to prevent the valve butterfly switch from being inactive or jammed.
(4) During the compression of the packing at both ends, ensure that the axes (lever shaft, rocker shaft) are active and not jammed.
(5) All gaskets should be updated.
4, the disassembly of the control seat
(1) After the upper cover of the control seat and the cylinder block, the cylinder block and the base are assembled and marked, the short bolts in the fastening stud bolts of the upper cylinder and the base are removed and placed.
(2) The nuts that loosen the two long fastening bolts at the same time or separately are required to be carried out slowly (alternately when loosening separately) until they are loosened, and the bolts are placed and placed.
(3) Separate the upper cover of the control seat, the cylinder block and the base, and take out the piston, the door stem and the spring, and place them in a fixed position.
(4) Remove the split pin and the hexagonal slot nut so that the piston rod is separated from the piston and placed.
(5) Inspection and cleaning of the control seat.
1) Check that the inner wall of the piston cylinder should be smooth.
2) Check the cylindrical compression spring and record the length in the spring ** state for comparison with the front (rear) inspection.
3) Check that the piston rod and piston surface should be smooth.
4) Check that the sealing surface of the upper cover, cylinder block and base joint should be intact and cleaned.
(6) The loading of the control seat. The loading of the control seat is carried out in the reverse step of disintegration, and the following points should be noted:
1) Replace the sealed O-rings with new ones, and replace the temperature-resistant rubber and seals;
2) Silicone grease should be applied to the inner wall of the cylinder and the surface of the piston to ensure lubrication;
3) After the air control control seat is installed, the air stroke of the piston rod is verified by compressed air, which should meet the requirements of the manufacturer. The action of the piston rod should be continuous and without jamming.
(7) Overall verification. The control seat is fixed on the valve body and connected to the lever of the valve to open the compressed air joint for overall verification. Claim:
1) After assembly with the extraction check valve, the stroke of the compressed air switch shall comply with the stroke specified by the manufacturer.
2) During the switching process, the overall action should be continuous and there is no click phenomenon.
3) The opening indication of the valve should be verified correctly, and the action switch is checked together with the thermal control. The display of the opening and closing is in accordance with the actual position indication of the valve, and the verification is completed.
Second, the trap
1 Introduction
The steam turbine's hydrophobic system is an important part of the steam turbine thermal system, especially the steam turbine body, main steam, reheat steam and high and medium pressure valves, new steam trapping for the pump steam turbine, etc., when the unit starts the warm pipe, the requirements It can be normally and regularly drained, and when the unit is in normal operation, the valve is required to be reliably insulated without leakage. If these traps leak, the impact on the efficiency of the unit is very obvious.
In view of this, some important hydrophobic valves of the imported 300MW steam turbine unit adopt imported valves, and the structure type is a two-position stop valve operated by air control. The shut-off valve has the advantages of simple structure, good sealing and maintenance. The shut-off valve is equipped with a pneumatic control mechanism, which makes the valve quick and sensitive, and can better meet the requirements of the automatic control of the unit. The product of the US VALTEK company, the valve body part is the product of the United States ONVAL company. The structure of the valve is shown in the figure, and the structure of the air control device is shown in the figure.
2, steam trap maintenance
Since the valve is composed of two parts, the operating mechanism and the valve body, the disintegration is carried out in two steps.
(1) Demolition of the operating mechanism.
4) Remove the peripheral components such as the compressed air pipe inlet connector, solenoid valve, and action switch connected to the air control operating mechanism, and place them in a fixed position.
5) Remove the manual operation device of the operating mechanism and set it.
6) Loosen the spring compression bolts on the top of the operating mechanism.
7) Loosen the fastening bolts at the connection between the operating mechanism and the valve stem and move the fastening ring slightly upwards.
8) Loosen the connecting bolts on the Huff lock block that fixes the operating seat to the valve body, remove the two locking blocks respectively, and bolt the two locking blocks together and set them.
9) Loosen the connecting nut of the valve stem and the operating mechanism with a wrench until the operating mechanism is disengaged from the valve body, and the operating mechanism is placed.
(2) Disassembly of the valve body.
1) Loosen the fastening bolt on one side of the bonnet with an Allen key, and screw the fastening bolt from the other side by the thread. Place a thickness of about 1 mm in the middle slot of the bonnet fastening. The iron plate (diameter Ø35 ~ Ø40), tighten the fastening bolt with a hex wrench to further open the slot of the bonnet to increase the clearance.
2) Use a special wrench (or rubber hoe) to pull (or tap) the door cover so that the door cover rotates counterclockwise until it is unscrewed and placed.
3) Tap the outside of the packing gland with a copper rod until it is loose, and take out the packing gland.
4) Take out the door lever and the door core and set it.
(3) Inspection. After the valve is completely disassembled, all parts such as the sealing surface of the valve should be inspected.
1) Valve line inspection on valve seat and door core: Appearance inspection Valve line seal should be contacted all week, and there should be no defects such as grooves and blows that affect the seal.
2) The sealing surfaces between the valve stem, the valve casing and the packing gland should be in good contact.
3) There should be no foreign matter or impurities in the inlet and outlet of the valve.
(4) Maintenance treatment.
1) If the valve line has a blown phenomenon, the valve line in the valve core and the valve seat should be treated differently: the valve line on the valve core is driven out on the lathe at the original angle; the valve line on the valve seat is dedicated. The repair tool repairs the hard alloy sealing surface in the valve seat, and the amount of scraping is about 0.05-0.08 mm each time, and the amount of scratching is determined according to the actual condition of the valve line defect. After observing that the sealing surface has no dents, the valve wire is finely ground with an abrasive paste. After the valve wire is polished, the blue oil (or red powder) is uniformly applied to the sealing surface on the door core, and is fixed by a special sleeve and sent to the valve seat for sealing contact test. The sealing surface should be evenly and uninterrupted throughout the week.
2) If the filler in the stuffing box is a non-flexible graphite filler, it should be replaced with a flexible graphite filler. If it is originally a flexible graphite filler, it should be checked for damage and should be updated if it is damaged.
3) The sealing surface on the door rod (in contact with the packing) should be bright and rust-free, and the self-sealing surface in the valve seat and the lower part of the stuffing box should be polished.
4) The connecting thread surface at the top of the door stem should be clean and the connection should be active.
5) The threaded connection of the packing compression sleeve should be cleaned to make it easy to move. In order to ensure that it can be easily adjusted during normal operation of the unit.
(5) Loading. After the cleaning and inspection work is finished, all the connecting threads are coated with the anti-biting paint, and then the valve can be loaded. The installation is performed in the reverse step of the disassembly procedure.
(6) Adjustments and precautions.
1) After the operating mechanism is connected to the valve stem, the lower limit of the valve (off direction) is adjusted. When the door rod thread is screwed into the connecting nut of the manipulating mechanism, the compressed air is directly connected to the air inlet of the operating mechanism, the valve is operated and controlled, and the connecting nut is adjusted until the valve is closed and the seat and the valve body are connected. The lower section of the * has a gap of 3 to 5 mm. At this point, the initial adjustment is over (at this time the Huff lock block is not installed).
2) The air control opens the valve, so that the control frame is tightly connected with the valve body, the Harmon lock block is installed, and the fastening bolts are tightened.
3) The air control will switch the valve and adjust the opening indicator of the valve so that the position of the pointer of the valve matches the actual switch position of the valve.
4) After the peripheral devices such as solenoid valves and action switches are installed, adjust the calibration of 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.
Third, the regulating valve
The regulating valve is used to adjust the flow of the medium in the equipment and the pipe. The working principle is mainly to change the flow channel area between the valve core and the valve seat to achieve the purpose of regulating the flow. The structure has multi-stage throttling, rotary cylinder type, Sleeve plunger type, flat gate type and cage type. The large-scale thermal power plant has complex system and high requirements for medium regulation. Therefore, the regulating valve has wide application in the steam and water systems of the unit. With the continuous improvement of the automation degree of the unit, the regulation performance of the regulating valve is required. It is also constantly improving.
Regulating valves are used in power systems* for a wide range of electric and air-controlled adjustments in terms of their drive. Here we introduce a pneumatic control valve manufactured by FISHER. The structure of the regulating valve is shown in Figure 4-8, and the structure of the pneumatic control part is shown in Figure 4-9.
The regulating valve is composed of a valve cover, a valve body, a valve stem, a valve core and a valve seat, and the air control operating part is composed of a gas control head (including a rubber film, a compression spring, etc.), a solenoid valve, a compressed air tube and the like.
1, the valve disintegration
(1) Remove the compressed air pipe joint, solenoid valve, etc. connected to the air control operating mechanism.
(2) Loosen the nut connecting the transmission mechanism drive rod and the valve door lever, and loosen the door rod until it is disengaged from the transmission rod.
(3) Loosen the nut of the upper control unit bracket of the valve cover, and lift the air control device to set it.
(4) Loosen the valve cap bolt and take the cap together with the door rod to set it.
(5) Loosen the gland bolt, pull out the door stem and the door core from the cap, and set it.
(6) Take out the sleeve on the valve body and the split valve seat and sealing gasket on the valve seat, and place them in a fixed position.
2, clean up and check
(1) Check the valve line on the valve core and the valve seat, it should be in good condition, and there is no defect that affects the sealing effect. If there is a slight defect, the grinding method should be used to eliminate the grinding method; if there is a deep blow or pit, it should be repaired by lathe processing; if the valve line is seriously damaged and cannot be repaired, the spare parts should be exchanged.
(2) Check that the stem seal section should be clean.
(3) There should be no oxides and other impurities deposited and attached around the window of the inspection sleeve. If it is, it should be cleaned.
(4) Check the sealing surface between the valve line and the valve seat on the valve seat, which should be smooth and complete, without any dents, blisters and penetrating scratches that affect the sealing.
(5) Check that the sealing surface between the bonnet and the valve body is complete.
(6) Check the inside of the valve body, especially the inner wall of the outlet side, and there should be no obvious blow loss and thinning.
(7) Check the packing in the packing chamber and replace it if it is damaged.
(8) All sealing surfaces should be cleaned.
3, loading
The loading is performed in the reverse step of disintegration. Pay attention to the following points when loading:
(1) The gasket should be replaced with a new one.
(2) After the sleeve is assembled, the sealing surface of the upper end should be kept at the same height as the sealing surface on the valve body to ensure the sealing effect of the cover head and the valve seat.
(3) When the control seat is connected with the valve body, the nut of the transmission door rod should be tightened for easy adjustment.
4, adjust
After the valve is installed in place, the peripheral accessories such as the air control connector are installed in place, and the valve is adjusted with the relevant personnel of the thermal control.
(1) Turn on the compressed air, adjust the valve lever to the closed position, then operate the control device to open the valve, adjust the door lever to the closing direction for 2~3mm, and then the valve stem and the air control device. The nut is tightened.
(2) Adjust the position of the valve to the off position, adjust the opening indication of the valve to the zero position, and then operate the valve switch several times to confirm the full stroke switch of the valve.