The control valve has the characteristics of simple structure and reliable action. However, because it is in direct contact with the process medium, its performance directly affects the system quality and environmental pollution. Therefore, the control valve must be maintained and overhauled regularly, especially on bad and important occasions.
Key inspection parts: 1). The inner wall of the valve body. For the control valve used in the occasion of high-pressure difference and corrosive medium, the inner wall of the valve body and the diaphragm of the diaphragm valve is often impacted and corroded by the medium, and the pressure resistance and corrosion resistance must be checked.
2). During the use of control valve seat , due to the infiltration of the medium, the inner surface of the thread used to fix the valve seat is easy to be corroded, which makes the valve seat lose. Attention shall be paid during the inspection. For valves operating under high-pressure differences, check whether the sealing surface of the valve seat is damaged.
3). The valve core is a movable part during the regulation work, which is most seriously scoured and corroded by the medium. During maintenance, carefully check whether all parts of the valve core are corroded and worn, especially under the condition of high-pressure difference, the wear of the valve core is more serious (due to cavitation), which should be paid attention to. Replace the valve core when it is seriously damaged. In addition, pay attention to whether the valve stem has similar phenomena, or the connection with the valve core is loose.
4). Diaphragm "O" rings and other gaskets. Check whether the diaphragm and "O" gasket in the control valve is aging and cracked.
5). The sealing packing shall pay attention to whether the PTFE packing and sealing lubricating grease are aging and whether the mating surface is damaged. It shall be replaced if necessary.
1). The control valve type shall be comprehensively selected according to the process variables (temperature, pressure, pressure drop, and flow rate), fluid characteristics (viscosity, corrosivity, toxicity, suspended solids or fiber, etc.), requirements of the control system (adjustable ratio, leakage, and noise, etc.) and the pipe connection form of the control valve.
2). Generally, the through single and double seat regulating valves and ordinary sleeve valves with small volume, large carrying capacity, and advanced technology are preferred. Low S value energy-saving valve and fine and small regulating valve can also be selected.
3). The following valve list can be selected according to different occasions, such as:
Straight through single seat control valve
It is generally suitable for occasions with a small leakage, small flow, and small pressure difference before and after the valve. However, valves with a diameter less than 20mm are also widely used in occasions with large differential pressure;
It is not suitable for high viscosity or fluid containing suspended particles.
Straight through two seat control valve
It is generally applicable to occasions with lax requirements for leakage, large flow and large pressure difference before and after the valve;
However, it is not suitable for high viscosity or fluid containing suspended particles.
Sleeve control valve
It is generally suitable for occasions where the fluid is clean and does not contain solid particles.
Where the pressure difference between the front and back of the valve is large and the liquid may flash or cavitate.
Control ball valve
The industrial ball valve is suitable for occasions with high viscosity, fiber, granular and dirty fluids.
The regulation system requires a wide adjustable range (r up to 200 ∶ 1; 300 ∶ 1).
When the valve seat gasket is made of soft material, it is suitable for occasions requiring tight sealing.
"O" type ball valve is generally applicable to the occasion of two-position cut-off.
"V" type ball valve is generally suitable for the continuous regulation system, and its flow characteristics are approximately equal percentage.
Angle control valve
It is generally applicable to the following occasions:
Fluids with high viscosity or suspended solids (flushing liquid pipe can be connected if necessary);
Gas-liquid miscible phase or fluid easy to flash;
Where right angle piping is required.
High-pressure angle control valve
In addition to various occasions in 5), it is also suitable for occasions with high static pressure and large differential pressure. However, the material and structural form of valve internals must be reasonably selected to prolong the service life.
Eccentric rotary valve
It is suitable for occasions with large flow capacity, adjustable specific width (r up to 50 ∶ 1 or 100 ∶ 1), large differential pressure, and tight sealing.
Control butterfly valve
It is suitable for occasions with large diameter, large flow, and low-pressure difference;
Our butterfly valve wholesale is generally applicable to thick and turbid liquid and fluid containing suspended particles;
For occasions requiring tight sealing, rubber or PTFE soft sealing structure shall be adopted; For corrosive fluids, corresponding corrosion-resistant lining shall be used.
Three-way control valve
It is suitable for shunting and merging occasions where the fluid temperature is below 300 ℃ and is used for simple proportioning adjustment. The temperature difference between the two fluids shall not be greater than 150 ℃.
Bellows seal control valve
It is suitable for vacuum systems and occasions where the fluid is highly toxic, volatile, rare, and valuable.
Low-temperature control valve
It is suitable for low-temperature conditions and deep freezing.
When the medium temperature is - 100 ~ 40 ℃, it can be equipped with a heat sink (heat absorption here) and a flexible graphite packing valve. When the medium temperature is - 200 ~ - 100 ℃, the long neck low-temperature valve should be selected.
Low noise control valve
It is applicable to the occasions where liquid flash, cavitation, and gas flow rate at the valve contraction surface are greater than the sound speed and the estimated noise exceeds 95dB (a).
Self-operated control valve
It is suitable for occasions with small flow change, low regulation accuracy requirements, or difficult instrument air supply.
In the production process of a special process, the special regulating valve shall be selected according to the user experience.
1. The control valve should be installed vertically and upright on the horizontal pipeline. For control valves with nominal diameter DN ≥ 80mm, permanent supports shall be set on the front and rear pipes of the valve.
2. The installation position of the control valve shall be convenient for operation and maintenance. Platforms shall be provided if necessary.
3. The piping of the control valve group shall be compact and convenient for operation, maintenance and drainage.
4. Sufficient space shall be reserved for the upper and lower parts of the control valve to remove the actuator, valve internals, lower flange, and plug of the valve during maintenance.
5. When the control valve is used for high viscosity, easy crystallization, easy vaporization, and low-temperature fluids, thermal insulation and antifreeze measures shall be taken.
6. The ambient temperature of the pressure control valve working is generally not higher than 60 ℃ and not lower than - 40 ℃.
7. When the valve is installed in a place with vibration, anti-vibration measures shall be considered.
8. For the control valve without a valve positioner, a small pressure gauge indicating the control signal shall be installed on the diaphragm head.
9. When the control valve is used for fluid containing suspended solids and high viscosity, it shall be equipped with a flushing pipeline.
10. When installing the control valve, pay attention to making the medium flow in the direction of the calibration arrow of the valve body.
11. The control valve shall be checked and calibrated first and installed after pipeline purging.