How To Avoid The Failure Of Regulating Valve Correctly

- Aug 03, 2020-

Regulating valve is also known as control valve. In the field of industrial automation process control, it accepts the control signal output by the adjustment control unit and uses power operation to change the final control element of process parameters such as medium flow, pressure, temperature, and liquid level. Generally composed of actuators and valves. According to the characteristics of the stroke, the control valve can be divided into straight stroke and angular stroke; according to the power used by the actuator, it can be divided into three types: pneumatic control valve, electric control valve, and hydraulic control valve; according to their functions and characteristics There are three types of linear characteristics, equal percentage characteristics and parabolic characteristics. The regulating valve is suitable for air, water, steam, various corrosive media, mud, oil and other media. There will be some failures in the regulating valve during use. How to avoid these failures? Let’s take a look.

1. Cleaning method:

Welding slag, rust, slag, etc. in the pipeline cause blockage or jam in the throttle, guide part, and balance hole of the lower bonnet, causing strain and scratches on the valve core surface and guide surface, and indentation on the sealing surface Wait. This often occurs in the initial commissioning of new systems and after major repairs. This is the most common failure. In this case, it must be unloaded for cleaning to remove the slag. If the sealing surface is damaged, it should be ground; at the same time, the bottom plug should be opened to wash away the slag falling into the lower valve cover from the balance hole, and the pipeline Perform flushing. Before putting it into operation, let the regulating valve be fully opened, and the medium will flow for a period of time before being brought into normal operation. 

2. External flushing method:

When ordinary valves are used to adjust some media that are easy to precipitate and contain solid particles, they are often blocked at the orifice and guide. The flushing gas and steam can be connected to 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 regulating valve and make the valve operate normally.


3. Method of installing pipe filters:

For small-caliber control valves, especially ultra-small flow control valves, the throttle gap is extremely small, and there should be no slag in the medium. In case of blockage in this situation, install a filter on the pipe before the valve to ensure the smooth passage of the medium. Regulating valve with positioner, the positioner is not working properly, and its air passage orifice is blocked is the most common fault. Therefore, when working with a positioner, the air source must be handled. The usual method is to install an air filter pressure relief valve on the air source line before the positioner.


4. Method of increasing the throttle gap:

For example, the solid particles in the medium or the welding slag and rust that have been washed away from the pipeline cause blockage, jamming and other failures due to the failure of the orifice. You can switch to a throttle with a large throttle gap—the throttle area is open. Valve cores and sleeves such as windows and openings, because their throttling areas are concentrated rather than distributed around the circumference, the fault can be easily eliminated. If it is a single or double seat valve, the plunger valve core can be changed to a "V" shaped valve core or a sleeve valve. For example, a double-seat valve in a chemical plant is often stuck. It is recommended to switch to a sleeve valve and the problem will be solved immediately.

 

5. Medium flushing method:

Using the scouring energy of the medium itself, scouring and taking away things that are easy to precipitate and block, thereby improving the anti-blocking function of the valve.

Common methods are:

① Change to flow closed type use;

②Use streamlined valve body;

③Place the orifice in a place where the scouring is severe. When using this method, attention should be paid to improving the erosion resistance of the throttle material.

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