VAV variable air volume butterfly valve is an air-conditioning system that controls the temperature of an air-conditioned area by changing the air supply volume and also adjusting the air supply temperature. The system adjusts the air volume sent into the room through the variable air volume terminal device, and adjusts the air volume of the air conditioner accordingly to adapt to the air volume demand of the system.
The variable air volume butterfly valve can automatically adjust the air supply air volume of the air conditioner (adjust the air supply temperature when the air volume reaches a small amount) according to the change of the air conditioning load and the change of the indoor required parameters to meet the comfort requirements of the indoor personnel or other process requirements. At the same time, the speed of the blower is automatically adjusted according to the actual air supply volume, which reduces the power of the blower to a greater extent and saves energy.
VAV variable air volume butterfly valve contains the following components:
Controller (equivalent to the brain), angle actuator, linear stroke actuator, displacement sensor, electric door motor, anti-pinch infrared sensor, personnel area detector, foot switch, flow sensor, face wind speed sensor, temperature sensor, LCD display operation panel, lighting and other components.
Butterfly valve (mainly composed of valve body, valve stem, butterfly plate and sealing ring) is a simple regulating valve, and it can also be used for on-off control of low-pressure pipeline media. Ventilation butterfly valve is a non-closed butterfly valve. Ventilation butterfly valves are used in dusty cold air or hot air gas pipelines of ventilation and environmental protection projects in chemical, building materials, power stations, glass and other industries, as a gas medium to adjust the flow (unit: cubic meters per second) or cut off the pipeline control device. This type of valve should generally be installed horizontally in the pipeline.
Structural characteristics of vav variable air volume butterfly valve:
1. It is designed and manufactured by adopting a new structural form of welding of center-line disc plate and short structure steel plate, compact structure, light weight, easy to install, small flow resistance, large circulation, avoiding the influence of high temperature expansion, and easy to operate
2. There are no connecting rods, bolts, etc. in the air volume regulating valve, which is reliable in operation and long in service life. It can be installed in multiple positions, and is not affected by the flow of the medium. There are no connecting rods, bolts, etc., so it works reliably and has a long service life. It can be installed in multiple positions, and is not affected by the flow of the medium.
The company has always paid attention to product research and development, has a research and development team of more than 20 people, and has established long-term cooperative relationships with universities, research institutions and large state-owned enterprises. The R&D team adopts modern design theory and design technology, has more than 20 years of technical accumulation, and continuously creates novel, reliable, and customer-friendly personalized products for the field of automatic control. At present, we are constantly improving permanent magnet motors, permanent magnet motor drives and other products, and are committed to the popularization of permanent magnet frequency conversion.
When we discuss butterfly valves in a broad sense, it also includes various fixed air volume butterfly valves, variable air volume butterfly valves (constant air volume valves with actuators), and variable air volume VAV boxes (VAV BOX) modified from butterfly valves.
Criteria for distinguishing between “pressure independent valve” and “common valve”
The primary goal of the laboratory ventilation system is to ensure the safety of the operators. The fume hood system needs to capture and block harmful gases, which requires the control of the surface wind speed of the fume hood. First, the surface wind speed that is too high or too low is unacceptable. , too low will lead to ineffective capture, and too high will lead to turbulence and eddy currents, and will also cause harmful gases to escape. An effective control system needs to avoid the possible situations where the surface wind speed is too high or too low.
Formula: wind speed 0.5m/s ↓= cross-sectional area of viewing window / exhaust air volume ↓
There are two situations in which the exhaust air volume of the fume hood changes:
1. Reasonable variable air volume (VAV):
When the window is raised or lowered, or other factors (such as a larger person reaching the fume hood window) cause the cross-sectional area of the window to change, the “valve” can be “closed down” or “opened up” to change Exhaust air volume, so that the “wind speed on the surface of the exhaust cabinet” is constant;
2. Malignant variable air volume (interference from the main pipe):
When the window is not moved or the surface wind speed is not required to change, the change of wind pressure in the main pipe will also interfere with the “valve” on the top of the fume cupboard. Make the exhaust air volume of the fume hood “changes that should not occur”, thereby affecting the surface wind speed that should be stable at this time;
in conclusion:
A good “valve” can “quickly resolve” the “malignant variable air volume” caused by changes in external air pressure through its own adjustment ability. “Close down” or “Open up” makes the fume hood change the air volume reasonably, and cannot be affected by the pressure change of the outside world (main pipe).
This is what we advocate for the “fume hood valve” should have excellent “pressure independent”.
The difference between the application of “Venturi valve” and “Butterfly valve“
Compared with the butterfly valve, the main advantage of the Venturi valve lies in the two points of “true pressure independence” and “quick response”:
(1) Pressure-independent characteristics: “It should change only when it should change, and it should not change when it should not change”
During the operation of the fume hood, the most important factor affecting the wind speed on the surface of the fume hood is the pressure of the ventilation system pipe network. Due to the opening and closing of other fume hoods or ventilation equipment, or changes in other aspects of the pipe network, the pipe pressure of the fume hood will change. This change happens frequently.
If the fume hood system uses ordinary butterfly valves, the surface wind speed of the fume hood will change frequently, which is very detrimental to the safety of the laboratory. Even if the wind speed control system is used, it will only be adjusted after the surface wind speed changes. It will go through a series of sensing, calculation, adjustment, and oscillation processes, and at this time, the unsafe situation has occurred, because the pressure change of the pipe network may occur at any time, and relying solely on the wind speed control system will lead to slow and frequent control of the surface wind speed.
The fume hood control system using the venturi valve can solve the problem of the pressure change of the system pipe network, and the venturi valve can be automatically adjusted according to the pressure change of the pipe network. This process occurs at the same time with the pressure change of the pipe network, thus avoiding the need to adjust the process by the wind speed control system, and realizing fast and stable air volume control.
(2) Self-regulation “quickly”
In the process of opening or closing the adjustment door of the fume hood, the problem of needing to adjust the exhaust air volume of the fume hood will occur. The structural characteristics of the FDE Venturi valve can ensure its rapid response and adjustment time, usually to achieve its required air volume, which is equally fast in use. In the case of a large actuator, the FDE Venturi valve only requires the actuator to rotate 10 or 20 degrees, while the butterfly valve requires a larger angle.
(3) The ratio of the maximum air volume and the minimum air volume of the Venturi valve is: 20:1
Limitations of Butterfly Valve Users’ “Fixing the Dead”
People who use butterfly valves often take the following remedial measures, hoping to minimize the impact of mains pressure fluctuations on the suction of their fume hoods:
(1) Use a VAV BOX (some people call it a variable air volume adjustment box), and use a pitot tube to measure the air volume to self-adjust
Assemble the “butterfly valve + pitot tube + differential pressure sensor + local controller” together to make a VAVBOX.
When the fume hood is not moving and the air volume should not change, the VAVBOX equipped with the butterfly valve uses the pitot tube to sense the vicious air volume change caused by the pressure fluctuation of the main pipe, and then transmits the data to the small controller through the differential pressure sensor, and the small controller then adjusts the The actuator can be turned on or off, and the small controller belongs to the DDC control principle. The main disadvantage is that the action is slow and requires measurement, calculation and adjustment.
However, the biggest problem with this method is that the pitot tubes used for air volume measurement are directly exposed to the exhaust gas containing dust and magazines, which will soon be blocked and the accuracy will be lost.
Please see! Why is the VAV BOX not suitable for use in the exhaust direction?
Answer: The VAV BOX contains dust-sensitive devices such as pitot tubes, which can quickly fail due to clogging. In addition, no matter how well the VAV BOX is done, the ratio of the maximum air volume to the minimum air volume is only 10:1, which means that the adjustment accuracy is twice as small as that of the Venturi valve.
(2) Use the so-called “variable air volume butterfly valve”:
The so-called “variable air volume butterfly valve” is actually adding an actuator to the “constant air volume butterfly valve”!
Variable air volume butterfly = (constant air volume butterfly valve) + actuator
= (butterfly valve + airbag) + actuator
The constant air volume valve is not suitable for the fume hood. The airbag is installed on the device to achieve the purpose of constant air volume when the fume hood does not require variable air volume. The following figure is the internal schematic diagram of the constant air volume butterfly valve with airbag. When the pressure increases, the airbag expands, pushing the front baffle, reducing the cross-sectional area of the airflow through the butterfly valve.
This product is a cheap product specially “customized” by some foreign constant air volume valve manufacturers for Chinese consumers. Although the price is extremely cheap, it is almost “pressure related”, and there are still many problems in use:
Some “constant air volume butterfly valves” can’t actually be “fixed” at all. The air volume is still fixed with the pressure of the pipe network. The constant air volume valve can be fixed, but it cannot be changed when it should change. That is the real constant air volume valve.
Some “constant air volume butterfly valves” have serious air leakage and cannot be closed even if they want to close. The reason is that the airbags in these butterfly valves called “constant air volume butterfly valves” do not have a fixed elastic coefficient like springs, and the blades of the butterfly valves rotate during the rotation process. The flow curve is also not linear, so its accuracy cannot be guaranteed when applied to a VAV fume hood control system. The airbag is directly in the air flow range, and when the gas contains impurities such as dust, it will block and affect the accuracy. Especially when high temperature or organic gas is discharged, the airbag may be damaged. This type of butterfly valve has the most complaints in the market;
The air volume of some constant air volume valves is as small as 20%, so the adjustment ratio of the maximum air volume and the minimum air volume may be only 5:1.
(3) The pipeline static pressure method (VFD) that the butterfly valve has to use
The system using ordinary butterfly valve can control the pipeline pressure by ensuring the static pressure of the pipeline. The system pipe network pressure is stabilized by measuring, calculating and comparing the static pressure of the pipeline, and controlling the fan. The disadvantages of this method are:
The accuracy is not high, and the implementation cannot be guaranteed. The selection of the pressure point determines the control accuracy of the pressure. However, it is usually difficult to find a suitable point in the pipeline for the pressure of the pipe network, especially when the resistance of each exhaust equipment and the resistance of the pipeline are different. A suitable pressure setpoint cannot be found.
The response is slow. Controlling the fan in this way is a slow process, and the laboratory exhaust air control requires high speed. In this case, it is difficult to achieve the expected control target, and the situation mentioned above will still occur.
The electric air valve adopts a new generation of electric controller to precisely control the air volume. Intelligent operation and easy installation. It is widely used in laboratory ventilation equipment, industrial ventilation systems, and environmentally friendly waste gas treatment equipment.
The wind valve material is PP and PVC, which is characterized by anti-corrosion, anti-aging, price concessions, easy installation
The current manual air valve mold a molding, high strength, good sealing, smooth appearance, low resistance. Its specifications are diameter 63 mm, 75 mm, 90 mm, 110 mm, 160 mm, 200 mm, 250 mm, 315 mm. The diameter of this pneumatic equipment is more than 355 mm which can be customized.
China Xicheng Environmental Protection has 16 years of experience in the research and development, and production of industrial waste gas purification equipment. It has developed a new generation of RHV series Venturi variable air volume control valves with independent intellectual property rights, integrating high-speed intelligent control, automatic mechanical compensation, and pressure-independent control technology. Integration to meet the unique requirements for airflow control in industrial exhaust gas ventilation systems. The PP series Venturi variable air volume valve is mainly suitable for constant air volume control, bistable control, or variable air volume control.
1. Pressure-independent control: mechanical pressure compensation components are installed in the sliding valve body in the valve body, and automatic pressure compensation is carried out according to the pressure difference between the inlet and outlet of the air duct to ensure that the air valve maintains a constant air volume at the setpoint when the static pressure changes; the valve can be at the valve end The pressure drop is within the range of 150Pa~750Pa to achieve pressure independent control;
2. Accurate airflow control: through the positioning of the airflow speed controller component, the air volume can be quickly adjusted, and the air volume control accuracy is ±5%;
3. Large air volume adjustment control range: air volume 50m3/h~1100m3/h;
4. Quick response: Response time to control signal and air duct static pressure change: <1 second;
5. Anti-dust and maintenance-free: Compared with similar products of conventional butterfly valves, because this series of products have no airflow (or pressure difference) sensor, it avoids the occurrence of safety accidents that cause system failure to dirty sensors and improves the stability of the product And durability.
6. High anti-corrosion treatment: The valve body is made of PP plastic material. Yes, this product can operate safely for a long time under high-strength corrosive conditions;
7. High reliability, high quality, and low price, good service: domestically produced high-quality products, reliable operation, high quality, and low cost, and provide 24-hour service.
Typical applications of PP series Venturi variable air volume control valve:
1. Constant air volume control (CAV series): Suitable for situations where the set air volume is maintained when the static pressure changes.
2. Variable air volume control (VAV series): suitable for closed-loop feedback variable air volume control occasions.
The air volume control valve is also called the air control valve. It is an indispensable central air conditioning terminal accessory in the ventilation, air conditioning and air purification engineering of industrial plants and civil buildings. It is generally used in air conditioning and ventilation system pipes to adjust the air volume of branch pipes. It can also be used For the mixed adjustment of fresh air and return air.
Features
(1) The connecting pipe size of the split multi-leaf air volume regulating valve is the same as the rectangular air pipe size stipulated by the national ventilation duct standardization.
(2) The blades of the air volume regulating valve are split-opening and forward-opening, and are used as regulating valves in ventilation, air conditioning, and air purification systems.
(3) Tested and measured, the air-tightness of the air volume regulating valve is good, the relative air leakage is about 5%, and the regulating performance is good.
Scope of use
Air volume control valves are widely used in industrial, mining, and civil building HVAC systems, industrial waste gas purification systems, and are one of the key equipment to control ventilation modes in various environments.
Material and category
The common materials of the air volume control valve are PP material, stainless steel material, PP material, and galvanized steel plate. The most used in the industrial waste gas purification industry is the PP damper.
The air volume control valve installation is carried out in accordance with the national building standard design “Air Valve Selection and Installation”. described as follows:
1. For the damper products transported to the construction site, the installation unit should report to the supervisor for acceptance, and check the certificate, test report and installation instruction document according to the packing list, and verify the product model, specification, material, logo and Whether the control method meets the requirements of the design documents, it should be recorded and signed by all parties for confirmation.
2. Before installing the air valve in place, check whether its structure is firm and tight, and conduct a switch operation test to check whether it is flexible and reliable; the electric air valve shall be energized and tested one by one, and test records shall be made.
3. Before the air valve is in place, it must be checked whether its applicable scope, installation position, air flow direction and operating surface are correct.
4. The opening and closing direction and opening angle of the air valve should be accurately marked on the visible surface.
5. For air valves installed in high places, the manual operating device should be 1.5-1.8m away from the exposed or operating platform.
6. The effective distance between the operating surface of the air valve and the wall, ceiling and other equipment and pipes shall not be less than 200mm, and the air valve shall not be installed in the structural layer or hole. The slit width around the valve should be greater than 150mm.
7. Check whether the flange size reserved for the connecting air pipe, the matching drill diameter and hole distance, the flatness and parallelism of the flange surface, the material and thickness of the gasket, and the connection method of the non-metallic air pipe meet the requirements.
8. Check whether the position and method of the support and hanger meet the requirements of the specification or design documents. A single damper with a weight greater than 50kg should be provided with a separate support and hanger; electric damper should generally be equipped with a separate support and hanger; for soft non-metal air duct systems, a separate support and hanger should also be provided for the damper .
9. The air valve used in the clean ventilation system must be cleaned as required before installation, and the two ends must be sealed after reaching the corresponding clean standards, and the sealing plate can be removed after it is in place. The inner surface of the air valve of the scrubbing purification air conditioning system should be made of materials that do not drop fibers. The scrubbed air valve must not be stored in a room without walls, floors, doors and windows, and the temporary storage place must be kept clean.
