Electric Actuator
The valve electric device is a kind of machine used to remotely control the valve. It is divided into two types: multi-rotary type and partial rotation type with only 900 rotations. The former is used for gate valve, stop valve and throttle valve, and the latter is used for ball valve. Butterfly valve
The valve electric device is generally composed of a reducer, an electric appliance, an electric motor and a remote controller.
The role of the valve electric device is: in the fully closed or pre-adjusted position of the valve, it can stop automatically and send a signal; the indication of on-site and long-distance opening is consistent; when the valve is opened or closed more than the nominal output torque, Stop and signal automatically.
When selecting the valve electric device, the following points should be worked out:
1. The type of valve (gate valve, globe valve, throttle or ball valve, butterfly valve);
2. The maximum torque required to open or close the valve;
3. Working environment (explosion-proof or non-explosion-proof)
4. For the valve electric device for gate valve, stop valve and throttle valve, the following information must be submitted:
(1) According to the speed of the operation of the valve, select the speed of the valve electric device;
(2) According to the requirements of use, elect to order with or without on-site operation of the valve motor co-device;
(3) Calculate the required number of revolutions N of the valve actuator (ie, the number of revolutions of the stem nut or valve stem) based on the opening height of the valve.
Butterfly valve
Butterfly valve opening and closing device is a disc-shaped butterfly plate, in the valve body around its own axis of rotation, so as to achieve the opening and closing of the valve called the butterfly valve. The full opening of the butterfly valve is usually less than 900. The butterfly valve and the butterfly rod do not have a self-locking force. In order to position the butterfly plate, a worm gear reducer is added to the valve stem. The use of a worm gear reducer not only enables the butterfly plate to have a self-locking ability, so that the butterfly plate can be stopped at any position, and the operating performance of the valve can also be improved. Industrial special butterfly valve features high temperature resistance, applicable pressure range is also high, the valve nominal diameter large, the valve body is made of carbon steel, the valve plate seal ring with a metal ring instead of a rubber ring. The large-scale high-temperature butterfly valve is made of steel plate welding and is mainly used for high temperature medium smoke ducts and gas pipelines.
The advantages of the butterfly valve are as follows:
1. The opening and closing is convenient, rapid, labor saving, and the fluid resistance is small, and it can be operated frequently.
2. Simple structure, small size and light weight.
3. Mud can be transported with minimal liquid accumulation at the pipe mouth.
4. A good seal can be achieved at low pressure.
5. The adjustment performance is good.
The disadvantages of butterfly valves are as follows:
1. The use of pressure and operating temperature range is small.
2. Poor sealing.
The butterfly valve can be divided into offset plate type, vertical plate type, inclined plate type and lever type according to the structural form. According to the sealed form, it can be divided into two types, a relatively sealed type and a hard sealed type. Soft seals are generally rubber ring seals, and hard seals are usually metal ring seals.
According to the connection type can be divided into flange connection and wafer type connection; according to the transmission mode can be divided into manual, gear transmission, pneumatic, hydraulic and electric several. Butterfly valve installation and maintenance should pay attention to the following matters:
1. During installation, the flap must be stopped in the closed position.
2. The open position should be determined according to the rotation angle of the disc.
3. A butterfly valve with a bypass valve should open the bypass valve before opening.
4. It should be installed according to the manufacturer's installation instructions. The heavy-duty butterfly valve should have a solid foundation.
Ball valve
The ball valve uses a ball with a circular passage as the opening and closing part, and the ball rotates to open and close the valve with the valve stem. The opening and closing part of the ball valve is a holed sphere, which rotates around the axis perpendicular to the channel to achieve the purpose of opening and closing the channel. Ball valves are mainly used to open and close pipes and equipment media. The main advantages of the ball valve are as follows:
1. Suitable for frequent operation, quick and easy opening and closing.
2. Fluid resistance is small.
3. Simple structure, relatively small size, light weight, and easy maintenance.
4. Good sealing performance
5. Without limitation of the installation direction, the flow of the medium can be arbitrary.
6. No vibration, low noise.
The main drawbacks of ball valves are as follows:
The ball valve can be divided into floating ball valve, fixed ball valve, elastic ball valve and oil seal ball valve according to the structural form. According to the channel, it can be divided into straight energy type, angle type and tri-type, etc. The three-type can be divided into T-shaped and L-shaped two. Species. According to the connection, workers can be divided into three types: threaded connection, flange connection and welding type.
Ball valve installation and maintenance should pay attention to the following matters:
1. To leave the position of the valve handle
2. Cannot be used for throttling.
3. Ball valves with belt drive should be installed upright.
Regulating valve
Regulators are used to regulate the flow, pressure and level of the media. According to the signal of the regulation site, the opening degree of the valve is automatically controlled so as to adjust the flow, pressure and liquid level of the medium. Regulating valve points electric control valve, pneumatic control valve and hydraulic control valve. This manual mainly introduces two kinds of electric control valve and pneumatic control valve.
The regulating valve consists of an electric actuator or a pneumatic actuator and a regulating valve. Adjusted and usually divided into straight single-seat type and straight two-seat type two, the latter has the characteristics of large flow capacity, small imbalance and stable operation, so it is generally suitable for large flow, high pressure drop and leakage less occasions.
The circulation capacity Cv is one of the main parameters for selecting the regulating valve. The regulating capacity of the regulating valve is defined as: when the regulating valve is fully opened, the differential pressure across the valve is 0.1 MPa, and the fluid flow rate per hour is 1 g/cm3. The flow rate of the regulating valve, called the flow capacity, also called the flow coefficient, is expressed in Cv and the unit is t/h. The Cv value of the liquid is calculated as follows.
According to the size of the circulation capacity Cv check table, the nominal diameter DN of the regulating valve can be determined.
The flow characteristic of the regulating valve is the relationship between the relative flow of the medium flowing through the regulating valve and its opening degree under the condition that the pressure difference at both ends of the valve is kept constant. The flow characteristics of the control valve have linear characteristics, equal percentage characteristics and parabolic characteristics. The significance of the three fluence properties is as follows:
(1) Equal percentage characteristics (logarithms)
The relative stroke and relative flow of equal percentage characteristics are not in a straight line. The change in the flow rate caused by the change in the unit stroke at each point of the stroke is proportional to the flow at this point, and the percentage of flow change is equal. Therefore, its advantage is that when the flow rate is small, the change in flow rate is small, and when the flow rate is large, the flow rate changes greatly, that is, at different opening degrees, it has the same adjustment accuracy.
(2) Linear characteristics (linear)
Linear characteristics of the relative stroke and relative flow in a straight line. The change in flow caused by the change in unit travel is constant. When the flow rate is large, the relative value of the flow rate changes little. When the flow rate is small, the relative value of the flow rate changes greatly.
(3) Parabolic characteristics
The flow changes in proportion to the two sides of the stroke, and generally has an intermediate characteristic of linearity and equal percentage characteristics.
From the analysis of the above three characteristics, it can be seen that, in terms of its adjustment performance, the equal percentage characteristic is optimal, its regulation is stable, and the adjustment performance is good. The parabolic characteristic is better than the linear characteristic adjustment performance. According to the requirements of the application occasions, any one of the flow characteristics can be selected.
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