Valve disc root selection and replacement method Valve maintenance

Valve disc root selection and replacement method Valve maintenance

The disc root of the valve is used to seal the door rod or seal the disc, which can prevent the outflow of the working medium. The valve disc eradication plays a sealing role, but also requires small friction with the stem, should not hinder the stem action. The selection of valve disc root should be based on the working medium, pressure and temperature, the use of disc material and shape are not the same.
First, valve disc root selection
The disc root of the valve is used to seal the door rod or seal the disc, which can prevent the outflow of the working medium. The valve disc eradication plays a sealing role, but also requires small friction with the stem, should not hinder the stem action.
The selection of valve disc root should be based on the working medium, pressure and temperature, the use of disc material and shape are not the same.
Table 5-1 lists the classification, performance, and application range of common disk roots.
Table 5-1 Classification, performance, and application range of common disk roots Material pressure
Temperature (MPa)
(C) Medium cotton coil root cotton yarn braided cotton rope, oil immersed cotton rope, rubber cotton rope < 20~25 < 100 Water, air, oil hemp coil root twine, oil immersed twine, rubber twine < 16~20 < 100 common asbestos coil root oil and graphite impregnated asbestos wire < 4.5 < 250 water, air, steam, oil aluminum wire asbestos braided wire, Oil, graphite impregnated < 4.5 < 350 clip braided wire, copper wire asbestos, graphite impregnated oil < 6 < 450 high-pressure asbestos packing (line), with asbestos cloth for rubber adhesives, asbestos and flake powder mixture of < < 6 450 water, air, steam, graphite packing ring made of graphite, and between the ring filling silver graphite powder, mixed with stainless steel wire, To improve the life of < 14540 steam carbon fiber packing
(pan root) by pre-oxidation or carbonization of polypropylene fiber, impregnated polytetrachloroethylene emulsion < 20 < 320 various media fluorine fiber filler
(can be made into standard shape) PTFE fiber, impregnated PTFE emulsion < 35260 various media wire filler lead wire 230 oil copper wire 500 steam RSM-0 type
The flexible graphite sealing ring is a rectangular cross section circle < 32 for high pressure valves
Two, valve disc root replacement method
Valve packing need to change, want to put the old packing, but be careful not to damage the door rod, sealing plate and stuffing box, after all the old packing, you can change the new packing, new packing, first to choose size and performance meet the requirements of the packing, do not allow to high and low, used in large generation or smashed, and then packing should be cut into single circle, The counterpart of the disc root should be neatly cut into an acute Angle of 45°, and its length should be suitable. When cutting the disc root, the disc root can be tightly wound on the round rod with the diameter equal to the diameter of the valve stem, and then the incision line is recorded before cutting. Add the cut coil ring into the coil box one by one, and use the pressure cap or ** tool to pound the coil root and compacted each circle. The incision of each single coil root should be staggered by 90°, 180° or 90°, 180°.
Packing to the dosage and had pressed again appropriate allowance, the depth of the gland pressure into the packing room, not less than 10% of packing chamber height, should not be greater than 20% ~ 30%, and the tight packing gland, more uniform, the strength of the screw tight packing is good when rotate the valve stem, in order to check the packing tighten the extent of the valve stem, gland tight, should level off, no tilt phenomenon.
The installation of the shaped disc root, can be directly set on the upper end of the valve stem should be as far as possible to use the method of direct set of people, when the filler can not be directly set of people, can also use the method of incision lap.
Valve maintenance 1.1 Valve maintenance and installation points for attention
1). The valve should be placed in a dry and ventilated room, and both ends of the diameter should be sealed and dustproof;
2). Long-term storage should be inspected regularly, and the processing surface should be coated with oil to prevent corrosion;
3) Before valve installation, carefully check whether the mark is in accordance with the use requirements;
4). During installation, the inner cavity and sealing surface should be cleaned, and the packing should be checked to see whether it is pressed tightly, and the connecting bolts should be tightened evenly.
5). The valve should be installed in accordance with the allowable working position, but attention should be paid to maintenance and convenient operation;
6) In use, do not partially open the gate valve to adjust the flow rate, so as not to damage the sealing surface when the medium flow rate is high, it should be fully open or fully closed;
7). When turning the handwheel on or off, do not use other auxiliary levers;
8). Transmission parts should be lubricated regularly; The valve should always be oiled in the rotating part and the stem trapezoidal thread part
9) After installation, regular maintenance should be carried out to clear the dirt in the inner cavity, check the sealing surface and the wear of the valve stem nut;
10). There should be a set of scientific and correct installation standards, sealing performance test should be carried out in maintenance, and detailed records should be made for investigation
11) Other matters needing attention:
1) Valves should generally be positioned before pipeline installation. The pipe should be natural, the position is not hard pull, so as not to leave the prestress;
2) Before positioning the low temperature valve should be as far as possible in the cold state (such as in liquid nitrogen) to do the opening and closing test, flexible and no jamming phenomenon;
3) The liquid valve should be configured with a 10° tilt Angle between the stem and the level to avoid liquid flowing out along the stem and increase the cold loss; More importantly, it is necessary to avoid the liquid touching the sealing surface of the packing, so that it is cold and hard and loses the sealing effect, resulting in leakage;
4) the connection of the safety valve should be elbow to avoid direct impact on the valve; In addition to ensure that the safety valve does not frost, so as not to work failure;
5) the installation of the globe valve should make the medium flow direction consistent with the arrow marked on the valve body, so that the pressure on the valve top cone when the valve is closed, and the packing is not under load. But not often open and close and need to strictly ensure that in the closed state does not leak the valve (such as heating valve), can be consciously reversed, with the help of medium pressure to make it closed;
6) large specifications of gate valve, pneumatic control valve should be installed vertically, so as not to bias one side due to the weight of the spool, increase the mechanical wear between the spool and the bushing, resulting in leakage;
7) When tightening the pressing screw, the valve should be in a slightly open state, so as not to damage the sealing surface of the valve top;
8) After all valves are in place, they should be opened and closed again, and qualified if they are flexible and not stuck;
9) After the large air separation tower is cooled bare, the connecting valve flange is pre-tightened once in the cold state to prevent leakage at room temperature and leakage at low temperature;
10) It is strictly prohibited to climb the valve stem as a scaffold during installation
11) The high temperature valve above 200℃, because the installation is at room temperature, and after normal use, the temperature rises, the bolt is thermal expansion, the gap is increased, so it must be tightened again, called “hot tight”, the operator should pay attention to this work, otherwise it is easy to leak.
12) When the weather is cold and the water valve is closed for a long time, the water behind the valve should be removed. After the steam valve stops steam, the condensed water should also be excluded. The bottom of the valve acts as a wire plug, which can be opened to drain water.
13) Non-metallic valves, some hard brittle, some low strength, operation, opening and closing force can not be too large, especially can not make strong. Also pay attention to avoid object bump.
14) When the new valve is used, the packing should not be pressed too tightly to avoid leakage, so as to avoid too much pressure on the stem, accelerate wear, and open and close.
1.2 Operation system and operation site
1.2.1 During the construction, the construction contractor, the safety department, the factory production department and the construction unit shall fully coordinate to clarify the scope of responsibility for the operation.
1.2.2 The full-time responsible person shall work on site in their respective operating responsibility area.
1.2.3 When removing or installing the valve, the daily production within a certain range affected by this operation should be changed and arranged accordingly, and the medium in the pipeline should be cut off.
1.2.4 The operation site necessary for the operation shall be ensured at the operation site.
1.2.5 Support parts suitable for the weight of the valve shall be set at the operating site to prevent valve sag and pipe center offset.
1.2.6 After the completion of the operation, preparations should be made for the pressure test, air tightness test, non-destructive inspection and other inspection items.
1.2.7 Before the operation is finished, the pipe network shall be cleaned inside, and the blind plate on the pipe shall be confirmed to be removed, and the valve operated during the construction shall be restored to the opening and closing state before the construction.
1.3 Precautions for valve installation
1.3.1 Before valve installation, it shall be confirmed that the valve meets the design requirements and relevant standards.
1.3.2 When handling and installing valves, beware of bumps and scratches
1.3.3 Before installing the valve, the inside of the pipeline should be cleaned to remove impurities such as iron filings and prevent foreign bodies from inclusion in the valve seal seat. In addition, the valve should be installed in the closed state.
1.3.4 Hoisting valve operation. The VALVE SHALL BE CORRECTLY LIFTED AT THE SPECIFIED LIFTING POSITION, AND SHALL NOT BE LIFTED OR PULLED UNDER local force.
1.3.5 When installing the valve, it is necessary to confirm whether the flow direction of the medium, the installation form and the position of the handwheel meet the regulations.
1.3.6 Installation of flange connection valves.
(1) The flange surface of valve and piping should be free from damage, scratches, etc., and kept clean. In particular, the use of metal gaskets (oval or octagonal section), flange grooves and gaskets should be consistent, to be coated with red lead for matching, to ensure that the seal is in good condition.
(2) The perpendicularity of the flange surface on the pipe and the center line of the pipe and the error of the flange bolt hole should be within the range of the allowed value. Valve and piping center line should be consistent before installation.
(3) When connecting two flanges, first of all, the flange sealing face and gasket should be pressed evenly, so as to ensure that the flange is connected by the same bolt stress.
(4) When tightening bolts, use a wrench that matches the nut. When using oil pressure and pneumatic tools for tightening, pay attention not to exceed the specified torque.
(5) The fastening of flange should avoid uneven force, and should be tightened in order in the direction of symmetry and compatibility.
(6) After installation of flange, make sure that all bolts and nuts are firm and uniform.
(7) The material of bolts and nuts must meet the regulations. After fastening, the bolt head should be exposed from the nut two pitch is appropriate.
(8) Bolt and screw fastening, in order to prevent vibration caused by loosening, to use gaskets. In order to avoid adhesion between threads at high temperature, the thread parts should be coated with anti-adhesion agent (molybdenum disulfide) during installation.
(9) For valves above 200 degrees Celsius, the flange connection bolts, cover fastening bolts, pressure seal bolts and packing pressure cover bolts must be tightened again after the temperature rises
(10) The low temperature valve is installed in the state of atmospheric temperature. In practical application, when the medium passes through, it becomes a low temperature state. Due to the formation of temperature difference, flanges, gaskets, bolts and nuts, etc., shrink, and because the materials of these parts are not the same, their linear expansion coefficient is also different, forming a very easy to leak environmental conditions. From this objective situation, when tightening bolts at atmospheric temperature, the torque that takes into account the contraction factors of each component at low temperature must be adopted.
1.3.7 Installation of welded connection valves
(1) The machining of socket joints and butt welding groove should be correct and comply with relevant standards.
(2) During welding, to prevent iron chips and welded beans from invading the tube, tungsten inert gas welding should be used.
(3) When welding, the valve should be in a slightly open state.
(4) Welding materials should be correctly selected according to the valve and piping materials. When USING COATED electrode, check the storage condition of the electrode and confirm whether the suitable drying treatment for coated electrode is taken.
(5) Personnel engaged in electric welding operation shall meet the requirements of electric welding technicians.
(6) When heat treatment is required after welding, the time and temperature curve record of heat treatment should be checked.
(7) The welding parts shall be visually inspected or non-destructive inspected to confirm that there are no cracks, welding nodules, edge bites and other harmful defects.