Introduction of Valve type
History on valve type
Thirty years ago, almost all pneumatic valves were automatic valves. Factory or high-rise buildings, especially high-rise buildings, were installed with pneumatic valves. The automatic valve for air conditioner (AHU) of each floor including the machine room and the 63 building of the Seoul Metropolitan Police Agency is the pneumatic valve. Almost all now seem to have been replaced by electricity, but at the time it was the best way.
However, it is no exaggeration to say that these pneumatic valves have been pushed away by electric type in the field of building automation. The reason is simple. The electric automatic valve is easy to install and easy to control because the operation source is general electricity, but the pneumatic valve has a difficulty in management because the compressed air must be delivered to the valve unit by the tube. Now, the quality of the tube material that connects the compressed air has become higher, and the price has become cheaper. Thirty years ago, Dongguan was the only one, or had a special plastic tube, but it was difficult to get it because it was expensive.
Therefore, pneumatic control valves have many advantages, but they are only present in factories, that is, only a small part of them are left behind by electricity except for industrial equipment. In my company, I have also produced pneumatic automatic valves in the early 1980s and exported and sold in Korea. However, it has also come to a standstill by being pushed by an electric or electrohydraulic valve actuator.
However, in 2004, it began producing pneumatic valve actuators that were produced in the early 1980s. This is because demand is rebounding due to changes in the domestic and overseas markets, and air pressure is dominant in the industrial sector, and sales prices are reasonable. From now on, we compare the characteristics of the pneumatic control valve actuator and the electric type, and compare them technically.
Most pneumatic manufacturers have designed the valves to be pneumatic or electric, so they can be used only by replacing the actuator with pneumatic and electric type, depending on the application.
Structure and Principle Comparison
Next, the structure and operation principle of pneumatic, electric valve actuators will be examined.
(1) Pneumatic Valve Actuator
① Operation explanation
When the signal current 4 ~ 20mA is applied to ①, the position of the valve will be closed (0%) and the operation will be based on 20mA (100%). When air is introduced into the upper part of the air chamber, the diaphragm is pushed against the disc, pushing the spring force, pushing the disc downward and pushing the shaft down.
At this time, in the case of the proportional control, the inflow amount of the air is adjusted according to the signal, which is due to the function of the positioner connected to the shaft. At this time, if the input signal and the shaft position are the same, it stops at that position. Thus, the proportional control characteristic is obtained. In the above case, the opening operation is operated by air, and the closing state is executed by the return operation by the spring force. This is called unidirectional operation, and it is called direct operation.
In the opposite case, it is called a reverse action actuator. In the case of pneumatic actuators, there are advantages of high accuracy and long life due to few moving parts. If the air leaks from the spindle seal part, only the seal ring (O-ring) needs to be replaced. Therefore, there is a characteristic that the actuator itself has little trouble. However, in the proportional control type, the positioner may fail, (0-point) of the positioner is distorted. Therefore, if you look at the manual and adjust it, it will work again.
In the case of pneumatic actuators, the operating pressure of about 0.5 to 2.5 Bar is applied for proportional control, but it can be adjusted according to the process or application. Therefore, it is possible to adjust the supply pressure according to the specification of the valve within the limit of the allowable differential pressure of the fluid,
There is a point that it can be increased or decreased.
(2) Electric valve
When 24VAC is applied to the power terminal and a signal of 0 ~ 10VDC or 4 ~ 20mA of standard signal is inputted to the signal terminal, the forward / reverse rotation of the motor is determined by the built-in amplifier circuit and triac. The drive circuit compares the signal value with the input value of the feedback potentiometer that senses the position of the valve shaft. When the input signal is lower than the feedback value, the motor rotates in positive (+ , And if the signals are the same, the motor is stopped, resulting in a repetitive vertical reciprocating motion of the spindle of the valve.
In the case of a motor, the operation is performed by repetition of the rotation direction and stop of the motor. Therefore, the lifetime of the motor and the motor force affect the closing state of the valve. At this time, it is difficult to increase the size of the motor. Therefore, the rotation speed of the motor is amplified by using the reduction gear
. In this case, the speed of the motor used usually is 300 ~ 600 RPM synchronous motor, and the deceleration rate of the gear is i = 9600 ~ 14,000.
Therefore, the electric valve actuator has a life span of about 1 million cycles (about 5 years). Therefore, when the motor is replaced for 5 years, the life of the valve actuator can be extended again. At this time, if valve actuator is used less frequently, it can be used for more than 10 years. Also, unlike the pneumatic actuators, it is a disadvantage that the speed and the output (Nf) can not be controlled in the case of the electric motor type.
So far, we have studied pneumatic valves and electric valves. It is important to select according to application and function. At present, it is not an exaggeration to say that there is no maker to design and manufacture control valve in the domestic market. Even now, except for a few cases, imports are mostly imitated, some of which are complementary products.
As of 2004, domestic technology trends show that valve manufacturing technology developed in many fields. However, it seems that the creation of new technology through imitation mentioned above seems to be lacking. The reason for this is that in the field of control valves, there was no investment at the level of large enterprises, but localization and technological development were carried out by some engineers engaged in related industries. Therefore, it is merely simple imitation, and research and development due to the development of the company has not been carried out continuously.
In the meantime, Korea has experienced a major change in the industrial field in response to the national economic crisis called the IMF. The group that suffered a lot from the difficult economic situation was the technicians who sweat in the field of production and felt the moment when they tried to get into the field of machine technology with the determination to do something to overcome the trials. I have learned that I have been so neglected in the field. In the meantime, the biased tendency of the IT sector and management has weakened the industry-based technology. In addition, IT, BT, and NT are now pursuing technologies that are made up of two English alphabets. However, even if these new technologies are reversed, nothing can be done without the industry-based, usually speaking 3-D industry base. There is a control valve here, and since the process of making this control valve is all 3-D, it is a problem for engineers who do not have skilled workers to replace heavy labor.
There are many advantages of localization. First of all, we expect the standard and performance to be produced in European standard, so that delivery time is fast, A / S is fast, and the price is economical.