Working principle of valve electric device
Because the valve type is multifarious, in order to manufacture and use conveniently, the state has made uniform provisions on the compilation method of valve product model. The valve product model number consists of seven units that indicate valve type, drive type, joint and construction, sealing or lining material, nominal pressure and body material. The type of valve is used to represent the valve type, driving and connecting form, sealing ring material and nominal pressure and other elements. The composition of the valve type consists of seven units in sequence…
The type of valve is used to represent the valve type, driving and connecting form, sealing ring material and nominal pressure and other elements.
Because the valve type is multifarious, in order to manufacture and use conveniently, the state has made uniform provisions on the compilation method of valve product model. The valve product model number consists of seven units that indicate valve type, drive type, joint and construction, sealing or lining material, nominal pressure and body material.
The composition of the valve type consists of seven units in sequence (see table below)
1. Type code of valve
2. The code of transmission mode is expressed in Arabic numerals according to table 1-2
Note: ① Hand wheel, handle and wrench drive and safety valve, pressure reducing valve, trap omitted this code.
② For pneumatic or hydraulic: normally open with 6K, 7K; Normally closed with 6B, 7B; Pneumatic hand with 6S said. Explosion-proof electric operation “9B”.
3. The connection form codes are represented in Arabic numerals as specified in Table 1-3
Note: Welding includes butt welding and socket welding
4. Valve electric device is to realize the valve program control, automatic control and remote control indispensable driving equipment, its movement process can be controlled by stroke, torque or axial thrust size. Because the valve electric device working characteristics and utilization depends on the type of valve, device working specifications and valve position in the pipeline or equipment.
The electric device generally consists of the following parts:
Motor is characterized by strong overload capacity, large starting torque, small moment of inertia, short time, intermittent work.
Reduction mechanism for reducing the output speed of the motor.
Stroke control mechanism to adjust and accurately control the opening and closing position of the valve.
Torque limiting mechanism for adjusting torque (or thrust) to a predetermined value.
Manual and electric switching mechanism, interlocking mechanism for manual or electric operation.
The opening indicator shows the position of the valve during opening and closing.
First, choose the electric actuator according to the valve type
1. Angle stroke electric actuator (corner 360 degrees) is suitable for butterfly valve, ball valve, plug valve, etc.
The rotation of the output shaft of the electric actuator is less than one week, that is, less than 360 degrees, usually 90 degrees to realize the valve opening and closing process control. This kind of electric actuator is divided into direct connection type and base crank type according to the different installation interface mode.
A) Directly connected: refers to the form of directly connected installation of the output shaft of the electric actuator and the valve stem.
B) Base crank type: refers to the form in which the output shaft is connected with the valve stem through a crank.
2. Multi-rotary electric actuator (corner 360 degrees) is suitable for gate valves, globe valves, etc. The rotation of the output shaft of the electric actuator is greater than one week, that is, it is greater than 360 degrees. It generally needs more than one circle to realize the opening and closing process control of the valve.
3. Straight stroke (straight motion) is suitable for single seat control valve, two seat control valve, etc. The motion of the output shaft of the electric actuator is linear motion, not rotational.
Two, according to the production process control requirements to determine the control mode of the electric actuator
1. Switching type (open-loop control) Switching type electric actuator generally realizes the on or off control of the valve. The valve is either in a fully open position or in a fully closed position. This kind of valve does not need to accurately control the medium flow.
It is particularly worth mentioning that switching electric actuators can also be divided into split structure and integrated structure because of the different structural forms. This must be explained when selecting the type, otherwise it often occurs in the field installation and control system *** and other mismatches.
A) Split structure (usually called common type) : the control unit is separated from the electric actuator. The electric actuator cannot control the valve independently, but must be controlled by an external control unit. Generally, the external controller or control cabinet is used for supporting. The disadvantage of this structure is that it is not convenient for the overall installation of the system, increasing wiring and installation costs, and prone to failure, when the failure occurs, it is not convenient for diagnosis and maintenance, cost-effective is not ideal.
B) Integrated structure (usually referred to as integral type) : the control unit and the electric actuator are packaged as a whole, which can be operated locally without external control unit, and can be operated remotely only by outputting relevant control information. The advantages of this structure are convenient system overall installation, reduce wiring and installation costs, easy diagnosis and troubleshooting. However, the traditional integrated structure products also have many imperfections, so the intelligent electric actuator is produced.
2. Regulating type (closed-loop control) regulating type electric actuator not only has the function of switching type integrated structure, but also can accurately control the valve and adjust the medium flow.
A) Control signal type (current and voltage) Control signal of regulating electric actuator generally has current signal (4 ~ 20MA, 0 ~ 10MA) or voltage signal (0 ~ 5V, 1 ~ 5V). The type and parameters of control signal should be clear when selecting the type.
B) mode of work (electric on, electric off) regulating electric actuator working mode is generally electric on (take 4 ~ 20MA control as an example, electric on refers to 4MA signal corresponding to the valve close, 20MA corresponding to the valve open), the other is electric off type (take 4-20MA control as an example, electric on refers to 4MA signal corresponding to the valve open, 20MA corresponds to valve off).
C) Loss of signal protection Loss of signal protection refers to that when the control signal is lost due to line faults, the electric actuator will open and close the control valve to the set protection value. The common protection value is fully open, fully closed and in situ.
According to the requirements of the use environment and explosion-proof grade, the electric device of the valve can be divided into ordinary type, outdoor type, flameproof type, outdoor flameproof type, etc.
Four, according to the valve torque required for electric actuators the output torque of the valve opening and closing the required torque determines the output torque of electric actuator to choose how, generally is put forward by the user or by matching valve manufacturer, as the actuator manufacturer is only responsible for the output torque of actuators, normal valve opening and closing the required torque is determined by the valve diameter size, factors such as working pressure, But because of the valve manufacturer processing precision, the assembly process, so that different manufacturer production of the same specification valve required torque is also different, even the same specification with a valve manufacturer production valve torque is different also, was elected type actuator torque choice is too small will cause can’t normal open/close the valve, electric actuator must choose a reasonable range of torque.
Five, the correct selection of valve electric device based on: operating torque: operating torque is the main parameter of the valve electric device, the output torque of the electric device should be 1.2 to 1.5 times of the valve operation torque. Operation thrust: there are two main structure of valve electric device: one is not equipped with thrust plate, direct output torque; The other is equipped with thrust disc, the output torque through the thrust disc stem nut converted into output thrust. Output shaft rotation circle count: the number of laps valve electric actuator output shaft rotation with nominal diameter of the valve, the valve stem thread pitch, thread, according to M = H/ZS calculation (M for electric devices should satisfy the total number of rotating ring, H is height of valve opens, S for stem drive screw pitch, Z for the stem thread). Stem diameter: for multi-turn type stem valves, if the relatively large stem diameter allowed by the electric device cannot pass the valve stem of the valve, it can not be assembled into an electric valve. Therefore, the inner diameter of the hollow output shaft of the electric device must be greater than the outer diameter of the stem of the open stem valve. For some rotary valves and many rotary valves in the dark rod valve, although do not consider the stem diameter through the problem, but in the selection should also be fully considered stem diameter and keyway size, so that the assembly can work normally. Output speed: if the valve opening and closing speed is too fast, it is easy to produce water strike phenomenon. Therefore, appropriate opening and closing speed should be selected according to different operating conditions.
Post time: Jun-23-2022