Maintenance code for automatic control valve

1, Scope of application

This regulation can be used as the general regulation for the maintenance, maintenance and repair of pneumatic control valves (including general single-seat valves, double-seat valves, sleeve valves, ball valves, disc valves, etc.) made up of actuators (pneumatic film or cylinders) and valve bodies used in factories.

Maintenance code for automatic control valve

2, the working principle of the control valve

Control valve by the actuator (pneumatic film or cylinder) and valve body parts composed of two parts. The actuator is the driving device, it produces the corresponding thrust force according to the signal pressure, so that the push rod produces the corresponding displacement, thus driving the valve core or valve plate action; Valve body parts are regulating parts of the valve, it is directly in contact with the medium, by the action of the valve core or valve plate to change the throttle area of the valve, to achieve the purpose of regulation. The actuator works on the principle of force balance, and the regulating valve works on the principle of fluid throttling.

3, Matters needing attention

1. System alignment shall be done before the regulator is put into operation.

2. When the section valve is working, the front and rear shut-off valves should be fully opened, and the bypass valve (auxiliary valve) should be fully closed. Other valves in the entire pipeline system should be opened as wide as possible, and normally the control valve should work within the normal use range (20%-80%).

3. Pay attention to the position indication mark of the handwheel when using the regulating valve with handwheel.

4. It is strictly prohibited to adjust the position of the valve stem and compression spring during the operation of the regulating valve.

4, Inspection of regulating valve

1. Check whether the air source pressure of each regulating valve is normal, whether the fastener of the air path (instrument air pipe, filter pressure reducing valve, valve positioner, etc.) is loose and whether the instrument air is leaking during the patrol.

2. During the inspection, check whether the packing box and flange connection has the process medium leakage, whether the valve stem connection is tight, whether the valve stem has the serious friction scratch or deformation.

3. Check the protection of the instrument line during patrol inspection, and check whether the inlet of the instrument is sealed well.

4. Check whether the valve stem movement is stable, whether the stroke corresponds to the output signal basically, whether there is rust in all parts of the valve, focusing on the valve stem, fasteners, cylinders and so on.

5,  Maintenance of regulating valve

1. Maintenance mainly refers to lubrication and cleaning of valve parts to extend the service life of valve parts.

2. Regularly clean and keep clean, especially the active parts such as the valve stem and the feedback lever of the positioner; Cleaning is usually done once every half a month; For the filler that needs to add lubricating oil, generally add oil once a week, and make the lubricator has enough oil stored, the variety of lubricating oil shall not be changed at will.

6, Maintenance of control valve

1. Before for regulating valve repair, need to fill in the maintenance working ticket, agree and sign the consent of the scheduling and process personnel, personnel to process closed globe valve before and after adjusting valve, if there is a leak cut-off valve, should be equipped with blind plate, and the bypass valve adjustment, technology personnel on-site monitoring various security measures in place, after being in cooling medium, and pressure relief valve, regulating valve could be performed in the maintenance and repair.

2. General procedures of maintenance:

Marking → (off line) → cleaning → disassembly → parts maintenance → grinding → degreasing (for oxygen valve) → assembly → adjustment and test → degreasing again (for oxygen valve) → (on line) → action inspection → circuit test → put into operation.

3. Marking: In order to ensure the correct reset of the regulator after off-line maintenance, attention should be paid to marking procedure. The following directions should be clearly marked

3.1 Connection orientation of valve body flange and pipe flange;

3.2 Connection orientation of the valve body with the upper and lower bonnet and their actuators.

4. To clean:

Some process media trapped in the valve body cavity is corrosive or toxic, before entering the dissolution process must be washed or steam purge, the control valve is impregnated with process media parts clean.

Disintegration of 5.

Note: for oxygen valves, oil must be banned during disassembly, including all valve components, disassembly tools and worktables.

5.1 The air-opening control valve shall add appropriate air pressure signals to the film air chamber or cylinder to make the spool or disc out of contact with the seat, and then rotate the stem to separate it from the push rod of the actuator.

5.2 Before disassembling the cylinder and valve body, the pretension of the spring in the cylinder must be released to avoid injury during disassembling. If necessary, it is necessary to completely decompose the actuator assembly and check the film, cylinder, spring and other wearing parts.

5.3 Parts obtained after valve decomposition should be stored centrally to prevent loss or damage.

6. Parts maintenance

6.1 Rust removal and cleaning of rusty or dirty parts shall be carried out by appropriate means. The machining surface shall be cleaned carefully, especially the sealing surface of the valve stem, spool, disc and seat shall be protected well.

6.2 Key inspection parts

6.2.1 Body: The inner wall of the body and the internal thread connecting the seat are vulnerable to corrosion and erosion by the fluid medium.

6.2.2 Seat: Sealing surface and external threads connected with body are subject to corrosion and gas corrosion.

6.2.3 Spool, spool plate and stem assembly: the sealing surface and regulating surface of spool and spool plate and the guide cylinder are vulnerable to corrosion and wear; The upper part of the valve stem shall not be loose in contact with the sealing packing, and the valve stem shall not be bent. If the connecting pin between butterfly valve plate and rotating shaft is loose or broken, and if the shaft sleeve is worn out, replace it as appropriate; Whether the valve plate and shaft are deformed and bent; Level Ⅳ sealing butterfly valve plate seal face should not have scratches, or to replace the new spare parts.

6.2.4 Corrosion in the packing gland of the upper bonnet.

6.2.5 Corrosion degree of flange sealing surface of valve body, upper cover and lower cover.

6.2.6 Repair or replace the thin film and "O" shaped sealing rings in the actuator according to the degree of aging and crack damage. Whether there are scratches on the inner wall of cylinder actuator and cylinder, whether the spring in actuator is deformed or corroded, repair or replace as the case may be.

6.3 According to the different damage conditions of parts, it is decided to adopt updating or repairing treatment.

6.3.1 The parts that must be renewed for each overhaul, whether damaged or not, shall have sealing packing, flange gaskets and "O" ring seals.

6.3.2 Parts that are found damaged by inspection and cannot be guaranteed to work in the next operating cycle shall be replaced, such as film sheets, springs, etc.

6.3.3 Other parts and components shall be updated if they are seriously damaged; In case of minor damage, repair welding and machining can be used to repair it.

7. Assembly

Note: for oxygen valves, all components must be cleaned and degreased before assembly.

7.1 In the whole process of assembly, special attention should be paid to the alignment between each part.

7.2 When assembling the valve body and upper and lower bonnet, the diagonal "ten" word shall be tightened one by one. Lubricant should be applied to the bolts.

7.3 The following points shall be noted during the assembly of sealing packing:

7.3.1 When open packing is used, the opening of two adjacent packing materials shall be staggered 180° or 90°.

7.3.2 For the regulating valve requiring regular filling of lubricating oil, the stuffing box (also known as lantern ring) in the stuffing box shall be in a moderate position and aligned with the filling port.

7.3.3 Select appropriate lubricating sealing oil according to the material of packing.

7.4 When assembling the actuator and valve, pay attention to the marks made before disassembly to ensure that the relative orientation is restored to the original position.

8. Adjustment and test

8.1 The process shall be confirmed before the adjustment and test of the regulating valve, and the Debugging Record of the Regulating valve shall be filled in carefully during the calibration process.

8.2 Basic error checking

The input signal is given to the valve positioner in the direction of increasing and decreasing steadily, and the stroke value corresponding to each point is observed. The test points are five points of the input signal range, namely 0%, 25%, 50%, 75% and 100%. The deviation of each point should be ±1% or so.

8.3 Return error check

The maximum difference of positive and negative travel measured at the same input signal is the backslip. Expressed as a percentage of the rated stroke of the regulating valve, it shall not exceed 1.0%.

8.4 Always point deviation check

Add the upper and lower limits of the input signal to the positioner respectively, and measure the corresponding stroke value. The deviation should not exceed 1%. Special attention should be paid to ensure that the starting point and the ending point of the gas opening control valve are in the valve closing position.

8.5 Dead zone calibration

The input signal is checked at 25%, 50% and 75% of the input signal by slowly changing (increasing or decreasing) the input signal until a perceptible stroke change (0.1mm) is observed. At this point, the difference between the input signals in the positive and negative directions is the dead zone. It should not exceed 3% of the full range.

9. After the valve is repaired and installed tightly according to the requirements, after passing the debugging, the technician shall open the globe valves before and after and close the bypass valves. After the adjustment is stable, fill in the maintenance Work Ticket completely and clean up the site, so as to achieve "completion of work, static materials and clear site".

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