In the higher degree of automation of chemical control system, regulating valve as the implementation of automatic adjustment system, the terminal device to receive control signals to achieve the regulation of chemical processes. It is directly related to the sensitivity of the action-conditioning systems quality. According to the site of about 70% of the actual statistics of the failures come from regulating valve. Therefore, routine maintenance review and analyze the impact the safe operation of control valve factors and countermeasures.
Card blocking
Valve recurring problem is that card blocked, often appear in the new transport system and the overhaul of investment put into operation in the initial stage, due to pipe welding slag, rust, etc. at the cutting mouth, oriented so that part of blockage caused by poor circulation media, or regulating valve repair in the tight packing, resulting in increased friction, leading to large-signal small-signal non-action motion overshoot phenomenon.
Troubleshooting: You can quickly open, off-line or adjust the valve, vice, so that dirt from the Vice-line or adjust the valve was washed medium run. Another way to stem tube clamp tight, plus the signal pressure in the case, the positive and negative force rotating stem, so that spool flash card office. If it is not an increase of gas pressure to increase the drive power source has repeatedly moved up and down several times, you can solve the problem. Should the motion not, it would take the disintegration of treatment.
Leakage
Valve leakage, valve stem length of the discomfort. Air to open valve, stem long stem up (or down) the distance is not enough, resulting in gaps between the valve core and valve seat can not be full access, leading to lax customs and internal leakage. Similarly, gas off valve stem is too short, resulting in gaps between the valve core and valve seat can not be full access, leading to lax customs and internal leakage.
Solution: should be shortened (or extended) regulating valve stem so that the length of the right valve so that it no longer internal leakage.
Packing leakage
Packing into stuffing after the axial pressure imposed by the gland. Because the plastic filler to produce a radial force, and close contact with the valve stem, but this contact is not very uniform. Some parts of the loose contact with some parts of the tight contact with, or even no contact at some parts. Regulating valve in the use process, the stem with the filling between the relative movement, this movement is called axial movement. The use of the process, with the high-temperature, high pressure and permeability of fluid medium strong, regulating valve packing leak letter is part of larger phenomena. Is mainly due to leakage caused by filler interface leakage, will appear for the textile and packing leakage (pressure medium along the filler-gap between the small outward leak). The interface between the stem and the packing leakage is due to the gradual attenuation of the contact pressure filler, filler causes such as their own aging, when the pressure medium will be along the contact between the filler and the valve stem outward leakage gap.
Countermeasures: In order to facilitate the filler loading, in the stuffing to the top chamfer, in the stuffing box placed at the bottom of the smaller gap erosion-resistant metal protection ring (with the contact surface can not fill slope) in order to prevent the fill material was medium pressure introduced. Stuffing box packing contact with the ministries and part of the metal surface to be finished, in order to improve the surface finish and reduce packing wear and tear. Flexible graphite packing selected because of their good gas tightness, the friction is small, changes after long-term use of small, wear the burning of a small, maintenance easy, gland bolts re-tightened after the friction does not change, pressure and resistance heat well, is not within the medium erosion, with the stem and the stuffing does not occur within the contact with the metal pitting or corrosion. In this way, the effective protection of the valve stem seal stuffing to ensure the reliability of sealing packing and long-term.
Valve core, valve leakage deformation
Valve core, valve leakage was mainly caused by the production process control valve in the casting or forging defects can lead to corrosion strengthened. The corrosive medium through the fluid medium can also result in erosion control valve leakage. Erosion or corrosion mainly exists in the form of cavitation. When the corrosive medium through the valve, it will give rise to spool, valve seat materials, erosion and impact so that valve core, valve seat into an oval or other shape, as time goes on, leading to valve core, valve seat is not matching, there is clearance, Guan lax leak.
Solution: The key to a good valve core, valve seat material selection customs, quality. Select corrosion-resistant materials, Ma points, trachoma and other defective products and resolutely removed. If the valve core, valve seat deformation is not serious, can grind through the fine sandpaper to remove traces, improve sealing finish to improve sealing performance. If serious damage, it should be re-replaced with new valves.
Oscillation
Control valve spring stiffness of inadequate control valve output signal instability could easily cause a drastic change in valve oscillation. Also that the election of the frequency of the system valve or pipe the same frequency, base severe vibration, so that control valve resulting vibrations. Selection of improper valve working in a small opening there is a violent flow resistance, velocity, pressure changes, when more than valve stiffness, stability deteriorated, severe oscillation.
Solutions: As the oscillation are many reasons, so the concrete analysis of specific problems. A slight vibration vibration, can increase the stiffness to eliminate. Chooses to use the large stiffness of spring, use piston implementation structures. Pipeline, the base support by increasing the elimination of severe shock vibration interference; selected valve the same as the frequency and system frequency, then switch to a different structure of the valve; work in the small openings caused by the oscillation, it is improper selection of flow capacity of C values of selected large, Selection of capacity C must be re-circulation of the value of the smaller or using sub-process control valves, or Picture-regulating valve in order to overcome the work of a small opening.
Valve Positioner Fault
Ordinary locator using mechanical force balance principle, namely nozzle baffle technology, mainly in the following fault types:
1) the use of mechanical force balance principle of work and its moving parts are more susceptible to temperature, vibration, resulting in control valve fluctuations;
2) The nozzle shield technology, due to the nozzle hole is very small, prone to dust or clean gas source block is the locator does not work;
3) Use of force balance principle, elasticity of the spring occurs in adverse changes in the scene, resulting in non-linear lead to the control valve decline in the quality.
Smart Positioning is controlled by a microprocessor (cpu), A / D, D / A converter and other components, whose working principle and common Locator different. For a given value and actual value comparison of purely electric signal, is no longer a force balance. Therefore, to overcome the conventional force balance locator shortcomings. However, for emergency parking lot timely, such as emergency shut-off valves, emergency venting valve. These valves require stationary at a certain location, only an emergency occurs, it requires good movement. Prolonged stay in a location easy for the electric converter small-signal does not cause uncontrolled movements of hazardous situations. In addition, the valve position sensor for the potentiometer as a result of on-site, easy to change in resistance value caused by the small-signal non-action, large-signal full-hazards. Therefore, in order to ensure the reliability and intelligent positioning device availability, they must be frequently tested.
By regulating valve failure cause analysis and take appropriate treatment, improved methods will greatly enhance the utilization of regulating valve to reduce instrument failure rate, the process technology to improve production efficiency and cost-effective and energy consumption all have an important role in reducing can effectively improve the quality of conditioning systems, thereby ensuring long-cycle production plants running.
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