Electric actuators have different functions and types, which can be called electric valves when matched with valves. However, in the design and selection process, only focus on the parameters of the valve, and ignore or do not clearly define the relevant requirements of the electric actuator, which will not only make the electric valve performance poor, but also cause serious consequences in the process of use.
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There are many kinds of electric actuators selected according to the type of butterfly valve, and their working principles are different. Generally speaking, the switching control is realized by rotating the valve plate angle, lifting the valve plate and so on. When matching with electric actuators, electric actuators should be selected according to the valve type first.
(1) The rotation of the output shaft of the angle-stroke electric actuator is less than one cycle, i.e. less than 360 degrees, usually 90 degrees, to control the opening and closing process of the valve. According to the different ways of installation interface, this electric actuator can be divided into direct connection type and base crank type.
(2) The output shaft of multi-rotation electric actuator rotates more than one cycle, i.e. more than 360 degrees. Usually, multiple revolutions are required to control the opening and closing process of the valve. This kind of electric actuator is suitable for gate valve, globe valve, etc.
(3) The motion of the output shaft of linear stroke electric actuator is linear motion, not rotation. This kind of electric actuator is suitable for single-seat regulating valve, double-seat regulating valve, etc. According to the production process control requirements, the control mode of electric actuator is generally divided into switching type and regulating type.
Pressure loss after the flow of the medium through the valve (the pressure difference before and after the valve) will occur. This is because the flow regulating valve has a certain resistance to the medium. The medium needs some energy to overcome the resistance of the valve. Consider the design and manufacture of the valve from the perspective of energy saving and emission reduction in order to minimize the resistance of the butterfly valve to the flowing medium.
Opening and closing forces and moments are the forces or moments that must be applied to open or close the valve. When closing the valve, it is necessary to apply closing force and torque between the sealing surfaces of the two halves of the valve seat with specific pressure, and between the packing and nut threads between the stem and stem end to overcome frictional components such as bearings and friction. The maximum values of opening and closing forces and opening and changing closing torques required during the opening and closing of high-performance butterfly valves are at the last moment of closing or the initial moment of opening. When designing and manufacturing the valve, efforts should be made to reduce the closing force and torque.
The lifting speed is used to open or close the valve to indicate the required movement time. The opening and closing speed of the valve is generally not important, but in some cases the opening and closing speed is required to be fast to prevent accidents, and in some cases the valve is required to close slowly to prevent water hammer, etc. This should consider the choice of valve type.
This refers to the sensitivity of the butterfly valve to changes in media parameters in order to make a corresponding response. For valves such as throttling valves, pressure reducing valves, valves used to regulate media parameters and safety valves, traps with specific functions, the sensitivity and reliability of the function are very important technical performance indicators.
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1.2.1 Process variables
Temperature, pressure, pressure drop and flow rate, etc.
1.2.2 Fluid features
Viscosity, corrosiveness, toxicity, presence of suspended matter or fibres, etc.
1.2.3 The requirements of the regulating system
Adjustable ratio, leakage, noise, etc. The regulating valve pipeline connection form to choose a comprehensive regulating valve type.
1.2.4 In general, we prioritize small size, sizeable passing capacity, advanced technology, straight-through single and double-seated control valves, and standard sleeve valves. You can also choose low S value energy-saving valves and small regulating valves.
1.2.5 We can use the following control valves according to different occasions.
&#; The application of the control valves
It is generally applicable to the process requirements of small leakage, small flow, the valve before and after the pressure difference is small occasions. However, if its bore is less than 20mm, it can also be widely used for more significant differential pressure occasions. Similarly, it is also suitable for high viscosity or containing suspended particles in fluid events.
&#;Through double-seat valve
It is generally applicable to the leakage requirements are not strict, the flow rate is significant, and the pressure difference between the front and rear of the valve is important occasions. However, it is unsuitable for high viscosity or fluid containing suspended particles.
&#;Sleeve valve
It is generally suitable for applications where the fluid is clean and does not contain solid particles. It has a significant pressure differential between the front and rear of the valve and where the fluid may flash or cavitate.
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&#;Ball valves
It is suitable for high viscosity, containing fibers granular and foul fluids.
The adjustment system requires a wide range of adjustable (R up to 200:1; 300:1) occasions.
When the valve seat gasket is made of soft material, it requires a tight seal.
The &#;O&#; type ball valve is generally applicable to the occasion of a two-position cut-off.
&#;V&#; type ball valve is generally applicable to continuous adjustment systems. Its flow characteristics approximate to equal percentage.
&#;Angle type valve
It is generally suitable for the following applications.
High viscosity or suspended fluids (if necessary, can be connected to the flushing liquid pipe).
Fluids in mixed gas-liquid phase or prone to flash vapour.
Pipelines require right-angle piping occasions.
&#;High pressure angle type valve
It is suitable for high static pressure significant differential pressure occasions. However, the material and structure of the inner parts of the valve must be reasonably selected to extend the service life.
&#;Body separation type control valve
It is suitable for high viscosity, containing particles, crystals, and fiber fluid. When it is used for strong acid, strong alkali, or robust corrosive fluid occasions, the valve body should be selected with corrosion-resistant lining, valve cover, spool, and valve seat should be used corrosion-resistant pressure pad or the corresponding corrosion-resistant materials. Its flow characteristics are better than diaphragm valves.
&#;Eccentric rotary valve
It is suitable for large flow capacity, adjustable ratio wide (R up to 50:1 or 100:1), and considerable differential pressure, tight seal occasions.
&#;Butterfly valve
It is suitable for large bore, large flow, and low-pressure differential occasions.
It is also suitable for thick turbid fluid and fluid containing suspended particles.
It requires tight sealing occasions. We should use a rubber or PTFE soft sealing structure; the corresponding corrosion-resistant lining needs to be used for corrosive fluids.
&#;Three-way valve
It is suitable for diversion and merging where the fluid temperature is below 300°C. It is also used for simple proportional adjustment. The temperature difference between the two fluids should not be more significant than 150&#;.
&#; The application of the valves
It is suitable for solid corrosion, high viscosity. It is also ideal for fluids containing suspended particles as well as fibers. Also, for occasions where flow characteristics are not strictly required. However, due to the limitations of the diaphragm lining, we can only use it for applications where the pressure is less than or equal to 1MPa and the working temperature is less than 150°C.
&#;Bellows seal valve
It is suitable for highly toxic, volatile, rare, and valuable liquids for vacuum systems and fluids.
&#;Low temperature control valve
It is suitable for low-temperature working conditions and profound freezing occasions.
It&#;s the medium temperature at -100 ~ 40 &#;. We can choose the heat sink (here for heat absorption) plus a flexible graphite packing valve. If the medium temperature is at -200 ~ -100&#;, we should choose the long neck type low-temperature valve.
&#;Low S-value energy-saving regulating valve
It is suitable for process load changes or when the S value is less than 0.3.
&#;Low noise valve
It is suitable for liquid flashing, cavitation, and gas flowing at the valve shrinkage surface at a speed more significant than the speed of sound and the predicted noise exceeds 95dB (A).
&#;Fast shut-off valve
It is suitable for a two-position regulating system and process failure. We need the valve emergency open or close the occasion.
&#;Self-operated regulating valve
It is suitable for small changes in flow, and regulation accuracy requirements are not high or instrumentation gas supply difficulties occasionally.
In the unique production process, we should choose a special regulating valve according to experience.
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