Model and selection of self-operated control valve

1. Overview of self-operated regulating valve:
Self-operated control valve, also known as self-operated control valve, is a control valve that relies on the pressure and temperature of the medium flowing through the valve itself as an energy source to drive the valve to work automatically, and does not require an external power supply and secondary instruments.
Self-operated control valves are mainly divided into self-operated pressure control valves, self-operated differential pressure control valves, self-operated temperature control valves, and self-operated flow control valves.
1. Function of self-operated control valve:
All self-operated control valves use the feedback signal (pressure, differential pressure, temperature) at the valve output to transmit to the actuator through the signal pipe to drive the valve disc to change the opening of the valve to achieve the purpose of regulating pressure, flow and temperature.
2. Advantages of self-operated control valve:
Self-operated control valve is a new type of control valve. Compared with the manual control valve, its advantage is that it can be adjusted automatically; compared with the electric control valve, its advantage is that it does not require external power. Application practice has proved that in the closed water circulation system (such as hot water heating system, air conditioning chilled water system), the correct use of this valve can easily realize the flow distribution of the system; it can realize the dynamic balance of the system; it can greatly simplify the system Debugging work; can stabilize the working state of the pump, etc.
2. Classification of self-operated regulating valve:
Self-operated control valves are divided into two types: direct acting and indirect acting.
1. Direct action
The direct-acting control valve is also called a spring-loaded control valve. There are elastic elements in its structure: such as springs, bellows, and bellows-type temperature bulbs, etc., using the principle of balance between elastic force and feedback signal.
2. Indirect action
Indirect-acting regulating valve, a pilot (pilot valve) is added, which amplifies the feedback signal and then drives the main valve disc to change the valve opening through the actuator.
If it is a pressure regulating valve, the feedback signal is the outlet pressure of the valve, which is introduced into the actuator through the signal pipe.
If it is a flow control valve, there is an orifice plate (or other resistance device) at the outlet of the valve, and the pressure difference signal is taken out from both ends of the orifice plate and introduced into the actuator.
If it is a temperature control valve, there is a temperature sensor (or a temperature bulb) at the outlet of the valve to drive the actuator through the thermal expansion and contraction of the medium in the temperature sensor.
3. Model of self-operated regulating valve:

ZZY type direct acting self-operated pressure regulating valve
ZZVP-16B type direct acting self-operated micro pressure regulating valve
ZZCP-16 type direct acting self-operated differential pressure regulating valve
ZZYP-16-2 pilot operated self-operated pressure regulating valve
ZZWPE type self-operated temperature control valve
ZZYVP-16B nitrogen sealing regulator
ZFQ-1 type explosion-proof fire-retardant breathing valve

4. Selection of self-operated control valve:
Self-operated control valve is a kind of automatic control valve that has been rapidly updated in technology and engineering application in recent years. It has been widely used in air conditioning, heating, municipal water supply and drainage, and chemical industry. It does not require external energy such as electricity and gas source, and can achieve more precise control of temperature, pressure, flow and other parameters only by the power of the medium itself. In today’s increasingly tight energy sources, its significance is self-evident. Moreover, it only needs to be set during debugging, and can be fully automatically controlled later, without additional sensors and controllers, which is convenient for control and saves equipment costs. It is really an irreplaceable new type of control valve. It is expected that In the future industrial automation control has a more and more broad market. Now, based on my many years of experience in the production and use of control valves, I will talk about the specific selection of self-operated control valves, and talk about Chen Guanjian, in order to attract others.
Let’s talk about the self-operated temperature control valve first. This kind of valve uses the probe to measure the temperature of the bulb or the storage tank. The change of the medium temperature causes the change of the volume of the expandable liquid in the probe, and there is a linear relationship between them. The pressure generated by the expanding liquid is transmitted to the piston through the capillary, which pushes the piston to move downwards, which in turn causes the valve core to displace, so as to control the flow of the medium, and finally control the temperature of the bulb, heat exchanger or storage tank. If steam is passed through, the valve core structure is generally flow-open type, that is, the valve core is downward to close; and if it is used to cool the storage tank or the temperature bulb (that is, the passing medium is cold water), the flow-closed type is required. structure, that is, the valve core moves downward to open. However, if the control valve is used behind the temperature bulb or heat exchanger, the temperature measurement point is still in the temperature bulb, and the internal structure of the selected self-operated temperature control valve is just the opposite. Grasp this principle, and there will be no major problems when selecting models. Of course, some other details cannot be ignored, such as physical and chemical parameters such as medium temperature and pressure. For example, a self-operated temperature regulating valve is used to control the flow of steam to heat the sulfuric acid in the storage tank, so that the temperature of the sulfuric acid is stabilized at a certain value, and the temperature measurement point is in the storage tank. Therefore, we must pay attention to the selection of probe materials, and 316L stainless steel should be selected, otherwise the service life of the control valve will be greatly shortened due to the non-corrosion resistance of the probe material during use. Of course, the control accuracy of this kind of control valve is generally only ±5%, which is lower than that of electric and pneumatic control valves, but the cost and convenience are its advantages. Moreover, there is now a variant of the self-operated temperature control valve, that is, the self-operated electronically controlled temperature control valve, which integrates the regulator and the controller in the electric actuator, collects the temperature signal through the thermal resistance, and performs the operation in the actuator. Compare, calculate, output control signal to drive the actuator motor, and then drive the valve. The control accuracy and reliability of this temperature control valve are better than the former.
The flow characteristics of the self-operated temperature control valve are generally quick opening, and it can also be designed as a linear type, and the temperature adjustment range is between 0 and 270 °C.
As for the self-operated pressure regulating valve and the self-operated flow and differential pressure regulating valve, the control principle is basically the same as that of the temperature regulating valve, so I will not repeat them one by one. The difference is that the former uses the membrane head as the actuator, and the medium directly enters the membrane head to drive the valve core. It should also be noted that when the pressure regulating valve is selected, if the medium is steam, a condenser must be added between the steam pipe and the membrane head, otherwise the steam will directly enter the membrane head and the membrane will be burned; The pressure point, that is, whether the regulating valve is used to control the pressure before the valve or the pressure after the valve, because the valve structure of these two working modes is different, it is often unclear when selecting and purchasing, and these problems are only discovered during use. It is futile to go back and forth, affecting production; the working pressure must also be clarified: generally, the diaphragm-type diaphragm head is used below 0.4MPa, and the piston-type diaphragm head is used above. As long as you know more about the working parameters of the valve when it is used, and then analyze it carefully, you can make the right choice and choose the ideal self-operated control valve for the customer.