How to select the right electric actuators for forged steel valve
Electric actuator of forged steel valve is an indispensable driving device for forged steel valve program control, automatic control and remote control. The movement process can be controlled by the stroke, torque or axial thrust. The working characteristics and utilization of the forged steel valve electric device depend on the type of forged steel valve, the operating specifications of the device and the position of the forged steel valve on the pipeline or equipment.
1. Forged steel valve electric actuators generally consist of the following parts:
- Specific motor, characterized by strong overload capability, large starting torque, small rotational inertia, short working time, intermittent operation
- Speed reduction mechanism to reduce the output speed of the motor
- Stroke control mechanism to adjust and accurately control the opening and closing position of the forged steel valve
- Torque limiting mechanism to adjust the torque (or thrust) and make it not exceed a predetermined value
- Manual, electric switching mechanism, interlocking mechanism for manual or electric operation
- Opening indicator to indicate where the forged steel valve is in the process of opening and closing
2. Select electric actuator according to the type of forged steel valve
Angular stroke electric actuator
Angle-stroke electric actuator (angle < 360 degrees) is suitable for forged steel butterfly valves, forged steel ball valves, forged steel plug valves, etc.
The rotation of the output shaft of the electric actuator is less than one circumference, that is, less than 360 degrees, usually 90 degrees, to achieve the opening and closing process control of the forged steel valve. Such electric actuators are divided into direct connection type and base crank type according to different installation interface modes.
- Direct connection type: It refers to the form in which the output shaft of the electric actuator is directly connected to the valve stem.
- Base crank type: It refers to the form in which the output shaft of the electric actuator is connected to the valve stem through the crank.
Multi-turn electric actuator
Multi-turn electric actuator (angle > 360 degrees) is suitable for forged steel gate valves, forged steel globe valves, etc.
The rotation of the output shaft of the electric actuator is greater than one circumference, that is, greater than 360 degrees. Generally, multiple turns are required to control the opening and closing process of the forged steel valve.
Straight stroke (linear motion) electric actuator is suitable for single seated forged steel regulating valves, two seated forged steel regulating valves, etc.
The movement of the output shaft of the electric actuator is linear, not in the form of rotation.
3. Electric device classified according to the operating environment and explosion-proof grade
According to the operating environment and explosion-proof grade requirements, the electric device of the forged steel valve can be divided into ordinary type, outdoor type, explosion-proof type, outdoor explosion-proof type, etc.
The output torque of the electric actuator is determined based on the torque required for the forged steel valve. The torque required for the forged steel valve to open and close determines the output torque of the electric actuator. It is usually recommended by the user or chosen by the forged valve manufacturer. An actuator manufacturer is only responsible for the output torque of the actuator. The torsion force required for the normal opening and closing of the forged steel valve is determined by factors such as the diameter of the forged steel valve and the working pressure. However, due to the difference in the machining accuracy and assembly process of the valve manufacturer, the torque required for the forged steel valves of same specification produced by different manufacturers is also different, even the torque of the forged steel valves of same specification produced by the same valve manufacturer is also different. If the torque of the actuator you selected is too small, the forged valve cannot be normally opened and closed. Therefore, for the electric actuator, a reasonable torque range is critical.
4. The basis for correct selection of the forged steel valve driving devices
The operating torque is the most important parameter for selecting the electric device of the forged steel valve. The output torque of the electric device should be 1.2~1.5 times of the maximum operating torque of the forged steel valve.
There are two types of main components of the valve electric device: one is that the thrust plate is not allocated and the torque is directly output; the other is to configure the thrust plate, and the output torque is converted into the output thrust through the stem nut in the thrust plate.
Rotation number of the output shaft:
The number of turns of the output shaft of the valve electric device is related to the nominal diameter of the forged valve, the pitch of the valve stem and the number of threads. It should be calculated according to M=H/ZS (M is the total number of rotations that the electric device should meet, and H is the height for valve opening, S is the stem transmission thread pitch, and Z is the number of stem thread ).
Diameter of valve stem:
For multi-turn type rising stem valves, if the maximum stem diameter allowed by the electric device cannot pass through the valve stem of the forged valve, it cannot be assembled into an electric forged valve. Therefore, the inner diameter of the hollow output shaft of the electric device must be larger than the outer diameter of the stem of the rising stem forged valve. For some of the rotary valves and the non-rising stem valves in the multi-turn forged valves, although the problem of whether the diameter of the stem can pass through the valve stem of the forged valve is put aside, the diameter of the stem and the size of the key groove should be fully considered in the selection, so that the forged valve can work normally after assemble.
Output rotational speed:
If the opening and closing speed of the forged valve is too fast, water hammer is likely to occur. Therefore, the appropriate opening and closing speed should be selected according to different conditions of use.
When using electric valves, various faults are often encountered. Valve leakage is a common type among many faults, and the leakage of electric valves generally has two situations: internal leakage and external leakage. So what is the difference between the two?
The internal leakage of an electric valve generally means that when the electric valve is completely closed, there is still a medium flowing out from the outlet of the electric valve. In general, the valve is not closed tightly, and the seal is not good. The cause of the failure is usually the erosion of the medium or impurities. Even if the electric valve screw (stem) is tightened, the media can still leak due to the gap between the valve plug and the valve body.
The external leakage of an electric valve generally refers to the leakage caused by poor external sealing packing between the electric valve and the connecting flange or the connecting thread. The sealing is nottight, so that the medium flows out of the connecting sealing surface, or there is a gap between the valve stem and the gland. External leakage can also be caused by holes on the valve body blank, or by wear of the valve body due to media erosion.
The main factors affecting the dead zone of the electric valve include friction, deviation, valve shaft torsion, the dead zone of the amplifier. Various control valves are not sensitive to friction. For example, rotary valves are very sensitive to friction caused by high seat loads, so pay attention to this when using them. However, for some seal types, a high seat load is necessary to achieve a shutdown rating. In this way, the design of the valve is very poor, and it is easy to cause a large dead zone. The influence of the process deviation is obvious and decisive.
How to select the right pneumatic solenoid valve
Slide gates and diverter valves that use pneumatic actuators (air cylinders) must be equipped with a properly matched pneumatic solenoid valve. The solenoid valve controls the flow of air pressure to the ports of the air cylinder to open or close a slide gate or switch a diverter. Solenoid valves are available in a number of different configurations based on their port size, flow factor and the application environment.
Single and Double Coil Solenoid Valves
The general rule of thumb is that a single coil solenoid valve is specified for slide gates and a double coil solenoid valve is specified for diverter valves. When a single coil solenoid valve is connected to a slide gate, it is plumbed to open the slide gate when the solenoid valve is energized and close it when de-energized. The advantage of doing this is that the slide gate will close upon loss of electrical power. This is called “fail closed”.
With a double coil solenoid, a momentary electrical signal is required to reposition the blade. The blade stays in the last position until the opposite coil is energized with another signal. In case of power loss, the blade stays where it is. This is called “fail last position”, which maintains the direction of the material flow.
Air Flow is Crucial in Delivering the Best Performance.
Each solenoid is rated for flow in liters per minute or by a flow coefficient (Cv) or flow factor (Kv). The rated airflow of the solenoid valve must meet the bulk handling valve manufacturer’s requirements of air demand to the air cylinder. If purchasing solenoids locally, make sure the air flow and other ratings are a perfect match to the solenoid specified by the valve manufacturer. Using a lower flow solenoid valve will cause performance problems such as chattering and slow actuation of the blade.
Solenoid valves are available in a number of environmental ratings to match system requirements. In North America, UL listings and NEMA ratings must be considered for the solenoid valve coils to ensure that the solenoid valve is appropriate for the environment in which it will be used. In the European Union, ATEX must be considered for both the solenoid valve body and the coils when used in hazardous locations. In other locations throughout the world, internationally accepted ratings such as IECEx may apply or country-specific ratings such as GOST-R may be required. Ingress Protection (IP), the degree of protection provided against the intrusion of dust and water, is an additional rating to consider.
Source: China Valves Manufacturer – Yaang Pipe Industry Co., Limited (www.ugsteelmill.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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