The welding slag, rust and slag in the pipeline cause blockage or jamming in the orifice, guide part and balance hole of the lower valve cover, resulting in pulling and scratch on the surface of the valve core and guide surface, and indentation on the sealing surface. This often occurs in the early stage of new system operation and after overhaul. This is a common fault of the company. In this case, it is necessary to remove the slag for cleaning, and grind if the sealing surface is damaged; 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 control valve shall be fully opened and the medium shall flow for a period of time before entering into normal operation.

When ordinary valve is used to regulate the medium which is easy to precipitate and contains solid particles, it is often blocked at the orifice and guide. Flushing gas and steam can be connected 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 work without moving the control valve, so that the valve can operate normally.

For small caliber control valve, especially ultra small flow control valve, its throttle clearance is very small, and there should be no slag in the medium. In case of blockage, a filter can be installed on the pipeline in front of the valve to ensure the smooth passage of medium. For the control valve with positioner, the positioner doesn't work normally, and the blockage of its throttle port is a common fault. Therefore, when working with the positioner, the air source must be handled well. The usual method is to install the air filter pressure reducing valve on the air source pipeline in front of the positioner

For example, the solid particles in the medium or the welding slag and rust washed out in the pipeline can not pass through the throttling orifice and cause blockage, jamming and other faults. The throttling parts with large throttling clearance, such as valve core and sleeve with windowed and open throttling area, can be used instead. Because the throttling area is concentrated rather than circumferentially distributed, the fault can be easily eliminated. If it is a single seat valve or a double seat valve, the plunger shaped valve core can be changed into a V-shaped valve core or a sleeve valve. For example, a double seat valve in a chemical plant is often stuck, so it is recommended to use sleeve valve, and the problem is solved immediately.

By using the scouring energy of the medium itself, it can scour and take away the things that are easy to precipitate and block, so as to improve the anti blocking function of the valve. The common methods are as follows: ① change to flow closed type; ② use streamlined valve body; ③ place the throttle orifice at the place with severe erosion, and pay attention to improve the erosion resistance of throttle material.

The straight through flow is inverted s flow, the flow path is complex, and there are many dead zones in the upper and lower cavity, which provides a place for the medium precipitation. Angular connection, the medium as if flowing through 90 ℃ elbow, good scouring performance, small dead zone, easy to design into flow line. Therefore, when the straight through control valve is slightly blocked, it can be changed to angle valve.

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