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Installation and Maintenance Best Practices for Loose Flange Connections

Installation and Maintenance Best Practices for Loose Flange Connections

Apr 09,2024

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Precautions for Purchasing Regulating Valves

Ⅰ. How to select the valve body type of the adjusting valve

There are many types of valve bodies for regulating valves. Common types of valve bodies include straight-through single-seat, straight-through double-seat, angle, diaphragm, small flow, three-way, eccentric rotation, butterfly, sleeve, spherical and so on. In the specific selection, the following considerations can be made.

1. The spool shape and structure

It mainly based on the selected flow characteristics and unbalanced force and other factors.

2. Wear resistance

When the fluid medium is a suspension containing a high concentration of abrasive particles, the internal material of the valve should be hard.

3. Corrosion resistance

As the medium is corrosive, one shall try to choose a adjusting valve with a simple structure.

4. The temperature and pressure of the medium

When the temperature and pressure of the medium are high and the changes are large, the valve core and valve seat materials should be selected with small changes in temperature and pressure.

5. Prevent flashing and cavitation

Flashing and cavitation only occur in liquid media. In the actual production process, flashing and cavitation will cause vibration and noise, which will shorten the service life of the valve. Therefore, when selecting the valve, one shall prevent the valve from flashing and cavitation.

Ⅱ. How to select adjusting valve actuator

In order for the adjusting valve to work normally, the equipped actuator must be able to produce enough output force to ensure a high degree of sealing and valve opening. According to double regulating valve working principle, there is generally no return spring for double-acting pneumatic, hydraulic and electric actuators. The magnitude of the acting force has nothing to do with its running direction. Therefore, the key to selecting an actuator is to understand the large output force and the rotating torque of the motor. For single-acting pneumatic actuators, the output force is related to the opening of the valve, and the force appearing on the adjusting valve will also affect the motion characteristics, so it is required to establish a force balance across the opening range of the adjusting valve.

Ⅲ. How to select the type of adjusting valve actuator

After determining the output power of the actuator, one shall select the corresponding actuator according to the requirements of the process environment. For explosion-proof requirements on site, pneumatic actuators should be used. From the perspective of energy saving, electric actuators should be used as much as possible. If the adjustment accuracy is high, a hydraulic actuator can be selected such as the speed adjustment of the transparent machine of the power plant, the temperature adjustment control of the catalytic device reactor of the oil refinery and so on.

Ⅳ. How to select the mode of action of the adjusting valve

The mode of action of the adjusting valve is only available when the pneumatic actuator is selected, and its mode of action is formed by the combination of the positive and negative effects of the actuator and the positive and negative effects of the valve. There are 4 types of combinations, namely, positive (air-to-close type), positive and negative (air-to-open type), anyway (air-to-open type), and reverse (air-to-close type). The adjusting valve action mode formed by these four combinations has are two types: on and off. Regarding the choice of the mode of action of the adjusting valve, it is mainly considered from three aspects.

1. The safety of process production.

2. The characteristics of the medium.

3. Guarantee product quality and small economic loss.

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