Practical methods to deal with leakage, blockage and jamming of electric control valve pneumatic control valve
Time: December 1, 2019 11:22:41 Source: Yonglong Valve Reading: zero second
Practical methods to deal with leakage, blockage and jamming of electric control valve pneumatic control valve
In industrial automation instrument control, control valve is a common valve, including electric control valve and pneumatic control valve. On the process pipeline, the working conditions are complex, once problems occur, it is difficult to find the problems accurately, and it also involves system operation, system completeness, regulation quality, environmental pollution, etc. The above Shanghai Yonglong Valve Factory recommends several practical treatment methods for you:
1、 Methods to prevent leakage of electric control valve and pneumatic control valve:
1. Replace the sealing gasket
Most of the sealing gaskets use O-ring PTFE sealing ring or flexible graphite, spiral wound gasket, "O" ring, etc. At high and low temperatures, particles and impurities in the medium are easy to cause wear and cause sporadic leakage of the valve stem.
2. Replace graphite packing method
As the working temperature of the widely used tetrafluoro filler is within the range of - 20~+200 ℃, when the temperature is at the upper and lower limits and changes greatly, its sealing property will decline significantly, and its aging is fast and its service life is short. Flexible graphite packing can overcome these shortcomings and has a long service life.
As a result, some factories have changed all the PTFE packing into graphite packing, and even the newly purchased control valve has changed the PTFE packing into graphite packing for use. However, the use of graphite filler has a large return difference, and some of them have creepage at the beginning, which must be considered.
3. Add filler method
In order to improve the sealing performance of the packing to the valve stem, the method of increasing the packing can be adopted. Usually, double-layer and multi-layer mixed fillers are used, and the effect is not obvious if the number of fillers is increased from 3 to 5.
4. Lens gasket sealing method
For the sealing of upper and lower covers, the sealing of valve seat and upper and lower valve bodies. If it is a plane seal, under high temperature and high pressure, the sealing performance is poor, causing leakage. Lens gasket seal can be used instead, which can achieve satisfactory results. If the medium is dangerous gas/liquid, it is recommended to use a regulating valve with bellows seal.
5. Change the flow direction and place P2 at the valve rod end
When △ P is larger and P1 is larger, sealing P1 is obviously more difficult than sealing P2. Therefore, the flow direction can be changed from P1 at the valve stem end to P2 at the valve stem end, which is more effective for valves with high pressure and large differential pressure. For example, seal P2 should be considered for bellows valves.
6. Add sealing grease method
For valves without sealing grease, it can be considered to increase sealing grease to improve valve stem sealing performance.
2、 Methods to prevent electric control valve and pneumatic control valve from being stuck or blocked:
1. Cleaning method
Common faults: welding slag, rust, slag, etc. in the pipeline cause blockage or jamming in the orifice, guide part, and lower bonnet balance hole, resulting in strain and scratch on the valve core surface and guide surface, and indentation on the sealing surface. This often happens when the system is newly put into operation and at the initial stage after overhaul.
In this special case, it must be disassembled for cleaning, and the slag should be removed. If the sealing surface is damaged, it should also be ground; At the same time, open the bottom plug to flush the slag falling into the lower valve cover from the balance hole, and flush the pipeline. Before putting into operation, the regulating valve shall be fully opened, and the medium shall flow for a period of time before being put into normal operation.
, 2. Change the straight through method to angular method
The straight flow is inverted S flow, with complex flow path and many dead zones in the upper and lower chamber, which provides a place for medium precipitation. Angular connection, the medium is like flowing through a 90 ℃ elbow, with good scouring performance, small dead zone, and easy to design into streamline. Therefore, when a straight regulating valve causes slight blockage, it can be used as an angle valve.
3. Pipe filter installation method
For small diameter control valves, especially ultra small flow control valves, the throttling clearance is very small, and there should be no slag in the medium. In this case, it is better to install a filter on the pipe in front of the valve to ensure the smooth passage of the medium.
For the control valve with positioner, the positioner does not work normally, and the most common fault is that the gas path orifice is blocked. Therefore, when working with the positioner, the air source must be handled well. The usual method is to install an air filter pressure reducing valve on the air source pipeline in front of the positioner.
4. External scouring method
For some media that are easy to precipitate and contain solid particles, when using ordinary valves for regulation, they are often blocked at the throttle port and guide, and flushing gas and steam can be connected externally at the bottom plug of the lower valve cover. When the valve is blocked or stuck, open the external gas or steam valve to complete the flushing without moving the control valve, so that the valve can operate normally.
5. Medium scouring method
Use the scouring energy of the medium itself to wash and take away things easy to settle and block, thus improving the anti blocking function of the valve. Common methods are:
Change to flow closed type;
Streamlined valve body is adopted;
Place the orifice at the place where the erosion is most severe, and pay attention to improving the erosion resistance of the throttle material when using this method.
6. Increase throttle clearance
If solid particles in the medium or welding slag and rust washed out in the pipeline are blocked or stuck due to failure to pass through the orifice, throttling pieces with large throttling clearance can be used instead - valve cores and sleeves with window and opening throttling areas. Since their throttling areas are concentrated rather than distributed around the circumference, faults can be easily eliminated.
If it is a single or double seat valve, the plunger valve core can be changed to a valve core with a "V" port, or it can be changed to a sleeve valve. For example, a double seat valve in a chemical plant is often stuck. After the sleeve valve is recommended, the problem will be solved immediately.
Electric control valve- Pneumatic control valve -Air drain valve - electric ball valve - pneumatic ball valve - emergency shut-off valve - electric shut-off valve- Ammonia stop valve -Transferred by Shanghai Yonglong Valve Factory
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