The ductwork damper is a system used in heating, ventilation, and air conditioning (HVAC) systems to regulate the flow of air through ducts. Dampers are usually adjusted by rotating vanes to restrict or increase airflow within the duct.
Duct dampers are usually located within the duct itself and can be manual damper or automatic damper. Manual dampers are adjusted manually, while automatic dampers are controlled by an electric motor or actuator that responds to changes in the HVAC system control signal.
Ductwork damper can be used to regulate airflow to specific areas of a building, or to regulate the amount of air delivered to different rooms or areas. They can also be used to control temperature and humidity levels within spaces.
The working principle of pipeline dampers involves a simple mechanism. Dampers consist of blades or plates that can be rotated or adjusted to control airflow. When the damper is open, it allows air to flow freely through the duct. When closed, it restricts the flow of air or blocks it entirely.
Automatic dampers are usually controlled by a thermostat or building automation system. The system can be programmed to open or close the damper based on temperature or airflow requirements. Through the HVAC system, the air volume passing through the air duct damper can be precisely controlled to achieve constant temperature and humidity indoors and maintain indoor air quality.
In summary, how a duct damper works involves blades or plates that can be rotated or adjusted to control airflow in an HVAC system. This allows precise control of air distribution and can improve energy efficiency and indoor air quality.
Installing a ductwork damper involves a few steps, and it’s essential to follow them carefully to ensure proper function and safety.
Here are the general steps to install a ductwork damper:
Gather the necessary tools and materials: You will need a screwdriver, duct tape, a drill, a hole saw, and a ductwork damper.
Turn off the HVAC system: To ensure safety, turn off the heating, ventilation, and air conditioning (HVAC) system.
Identify the location of the damper: Determine where you want to install the damper. Typically, it’s best to install the damper close to the duct’s source of airflow.
Cut a hole in the duct: Use a hole saw to cut a hole in the duct. The hole should be slightly smaller than the diameter of the damper.
Install the damper: Insert the damper into the hole in the duct, making sure that it’s securely in place.
Attach the damper: Use screws or duct tape to attach the damper to the duct. Make sure that the screws or tape are tight enough to hold the damper in place.
Test the damper: Turn on the HVAC system and check the damper’s function by adjusting its position. If it works correctly, turn off the system and close the damper.
Seal the damper: Use duct tape to seal the damper to the duct. This step ensures that the damper functions correctly and prevents air leaks.
Turn on the HVAC system: Turn on the HVAC system and check for proper airflow. Make any necessary adjustments to the damper’s position to achieve the desired airflow.
It’s essential to remember that installing a ductwork damper requires knowledge of HVAC systems and ductwork. If you’re not confident in your abilities, it’s best to hire a professional to install the damper.
An electric damper is a device used to regulate the flow of air or gas through a duct or vent. They are commonly used in heating, ventilation, and air conditioning (HVAC) systems to control temperature and humidity levels in buildings. They are also used in industrial applications, such as the automotive and aerospace industries, to control the flow of exhaust gases and other pollutants.
One type of electric damper that has become popular in recent years is the plastic electric damper. Made of durable, lightweight plastic material, these dampers offer several advantages over traditional metal dampers.
Main advantages of plastic electric dampers
Corrosion resistance: Unlike metal dampers, which can rust and corrode over time, plastic dampers are unaffected by moisture and chemicals, making them ideal for use in harsh environments such as chemical processing plants and wastewater treatment facilities choose.
Lightweight: Because they are made of lightweight materials, they are easy to install and require less support than heavier metal dampers. This can reduce installation costs and make them a more attractive option for retrofitting existing HVAC systems.
Energy-efficient and environmentally friendly: They use electric motors to open and close the damper blades, allowing precise control of airflow and reducing the energy required to run the HVAC system. Additionally, because they are made of lightweight materials, they require less energy to operate than heavier metal dampers, saving energy and lowering operating costs in the long run.
Low production cost: All accessories of some models of plastic electric dampers are made of PP plastic injection molding, which reduces more labor costs. It supports customized processing of various air valve sizes, because the raw material is recycled PP plastic material, which is currently the most cost-effective air damper product.
Plastic electric dampers are used in a wide range of applications including residential, commercial and industrial environments. In residential settings, they are often used to control the flow of air in HVAC systems to regulate the temperature and humidity levels in the home. They can also be used in commercial buildings, such as office buildings and retail stores, to maintain a comfortable and healthy indoor environment for employees and customers.
In industrial settings, plastic electric dampers can be used to control the flow of exhaust gases and other pollutants in manufacturing processes. For example, they can be used to regulate the flow of air in spray booths and other spray booths to prevent overspray and reduce the risk of fire and explosion.
Plastic electric dampers play a very important role in the laboratory ventilation system. Laboratory ventilation design has strict design requirements. The PP plastic electric air valve can be used to precisely control the discharge volume of the fume hood. Both the laboratory fresh air system and the exhaust system can use the plastic electric air valve to control the air volume.
In conclusion, plastic electrodynamic dampers are a versatile and energy-efficient solution for regulating the flow of air and gas in a wide range of applications. Their lightweight design and corrosion resistance make them ideal for use in harsh environments, while their precise control of airflow and energy efficiency make them a cost-effective choice for HVAC systems in residential, commercial, and industrial environments.
Polypropylene Electric Damper is a mechanical device designed to regulate or control the flow of air in HVAC (Heating, Ventilation and Air Conditioning) systems. These dampers are primarily used to regulate air volume, pressure and temperature in ductwork. Polypropylene electric dampers are known for their durability, high performance and low maintenance requirements. In this article, we will discuss in detail how polypropylene electric dampers work.
Polypropylene electric damper consists of frame, vanes and actuator. The valve body is made of polypropylene injection molding or PP board welding. Due to the strong corrosion resistance of polypropylene, polypropylene anti-corrosion dampers are usually used in highly polluted and highly corrosive chemical environments.
The working principle of polypropylene electric damper:
When the actuator opens, it rotates the vanes to the desired position, allowing air to flow through the ductwork. The position of the vanes determines the amount of air that is allowed through the damper. For example, if the blades are fully open, the maximum amount of air will pass through the damper, and if the blades are fully closed, no air will pass through the damper.
Polypropylene electric dampers can be controlled in a number of ways, including thermostats, timers, and sensors. The thermostat is used to regulate the temperature in the room, and when the desired temperature is reached, the thermostat signals the damper to close. A timer can be used to open and close the damper at specific times of the day, which is useful for energy saving purposes. Sensors can be used to detect if a room is occupied, and when the room is unoccupied, the damper can be closed to save energy.
Polypropylene electric dampers are also designed to be maintenance-free, meaning they require no regular lubrication or adjustments. They are also designed to be self-cleaning, which helps reduce the risk of contamination in the air ducts.
In addition to durability and low maintenance requirements, polypropylene electric dampers are also distinguished by their high energy efficiency. By regulating the flow of air through ductwork, these dampers can help reduce energy consumption and lower utility bills. This is especially important in commercial buildings, where HVAC systems are a major source of energy consumption.
Polypropylene electric dampers are also designed for easy installation, which helps reduce installation costs and minimize downtime. They can be installed in new or existing ductwork and can be customized to meet a building’s specific needs.
In summary, Polypropylene Electric Dampers are an essential part of HVAC systems used to regulate the flow of air through ductwork. They are durable, energy efficient and low maintenance, making them ideal for commercial and industrial applications. By understanding how polypropylene electric dampers work, homeowners and facility managers can make informed decisions about their HVAC systems and ensure they are operating at peak efficiency. Contact us.
Plastic duct damper is a damper used in heating, ventilation, and air conditioning (HVAC) systems to regulate the flow of air through the ductwork. Dampers are typically installed within ductwork and can be used to control airflow in a single direction, or to block or divert airflow entirely.
There are many different types of plastic duct dampers on the market, each with their own unique features and benefits. Some key factors to consider when selecting a plastic duct damper include the size of the ductwork, the type of HVAC system being used, and the specific application of the damper.
Key Benefits of Plastic Duct Dampers
Durability and Corrosion Resistance Unlike metal dampers, which can rust or corrode over time, plastic dampers are resistant to many types of chemical and environmental damage. This makes them ideal for harsh industrial environments as well as residential and commercial HVAC systems.
Easy to install Unlike metal dampers, which are bulky and difficult to work with, plastic dampers are lightweight and easy to handle. This makes them ideal for use in tight spaces where manipulating larger components can be difficult.
Types of Plastic Duct Dampers
Inline damper These dampers are installed within ductwork and can be used to control unidirectional airflow. Inline dampers are typically manually operated, using a lever or dial that allows the user to adjust the damper position as desired.
Steering damper These dampers are used to block or divert airflow within ductwork. Diverter dampers are commonly used in HVAC systems to control the flow of air between different areas or rooms and can be operated manually or through an automated control system.
In addition to in-line and split flow dampers, a variety of other plastic duct dampers are available including return flow dampers, volume control dampers. Backflow dampers are used to prevent backflow of air within the ductwork, while volume control dampers are used to regulate the flow of air within the system. Plastic air duct dampers can be made of flame-retardant PP/PVC, and the flame-retardant materials can
When selecting a plastic duct damper, it is important to consider the specific application of the damper. For example, if the damper will be used in an industrial setting, it may be important to choose a damper that is resistant to chemical and environmental damage. If the damper will be used in a residential or commercial HVAC system, it may be important to choose a damper that is easy to install and operate.
In addition to choosing the correct type of plastic duct damper, it is also important to ensure the damper is installed correctly. Improper installation can result in reduced efficiency and performance, and increased energy costs. It is important to work with a qualified HVAC contractor to ensure the damper is installed correctly and operating at peak performance.
In summary, plastic duct dampers are an important part of HVAC systems, allowing users to control the flow of air through the ductwork and improving the efficiency and performance of the system. There are many different types of plastic duct dampers on the market, each with their own unique features and benefits.
HVAC systems in commercial buildings are getting smarter every day. As technology advances, HVAC systems must adapt too. This growing “smart” building has brought huge benefits – energy management has tightened, tenant comfort has become more common, and cost savings have increased.
Let’s look at one smart HVAC system: VAV.
What is a VAV system?
VAV stands for Variable Air Volume. In its simplest form, a VAV system uses a changing airflow at a constant temperature to heat and cool a building. This is in contrast to CAV (or constant air volume) systems, which provide consistent airflow at different temperatures to heat or cool a space.
How does a VAV system work?
Let’s break down an example of how a VAV system works. The Air Handling Unit (AHU) pushes air through the ductwork at approximately 55 degrees Fahrenheit for cooling. The air temperature is kept constant in the system, moving through the ductwork to each area or room of the building. Air eventually reaches the end of each line and passes through the VAV box. Typically, a VAV box consists of a few simple parts: a damper, a controller/actuator, and maybe a coil for heating and cooling via electricity or a water pump.
As air passes through these boxes, actuators adjust the damper position, allowing different amounts of airflow into the area. Each VAV box adjusts to the needs of individual zones, meaning it can easily accommodate high demand in one area and low demand in another, keeping everyone comfortable. Additionally, if the damper is fully closed, the increased system pressure can slow down the AHU’s fans, thereby reducing energy consumption. Or use a bypass damper in the middle of the system, which may be triggered by increased pressure to open, relieving the system from additional ducting or external vents.
The benefits of variable air volume
The added control through VAV brings some benefits:
Precise temperature control
Reduce compressor wear
Reduce energy consumption
low noise
Waterproof and anti-corrosion
Xicheng control variable air volume products
The key components of these VAV systems are the actuators. These controllers are complex and fully programmable for application-specific functionality and any custom application you see fit. They also include integrated alerting, trending and scheduling to make powerful edge devices that can be controlled through BAS systems.
As buildings get smarter, so should your HVAC system. Having more control means more comfortable, lower cost and smarter buildings.
VAV is the abbreviation of Variable Air Volume. In the air conditioning system, in order to cope with the change of the terminal load, when the flow of the cooling/heating medium remains unchanged, the air volume needs to be adjusted to adjust the delivery of cold/heat to meet the changing demand.
Introduction to the control method of VAV variable air volume system
For the VAV system, the control methods can be generally divided into three types:
Constant and static pressure control: Its working principle is that in the system, the VAV BOX controller adjusts the air volume at the end to meet the load requirements according to the indoor load changes. The change of air output causes the change of static pressure in the system pipeline. The static pressure sensor measures the change of static pressure and transmits it to the fan inverter DDC. The inverter DDC controls the motor speed of the air conditioner according to the static pressure change signal, adjusts the total air output, and maintains The static pressure of the supply air piping system is constant.
Variable static pressure control: its working principle is that the system will try to keep the VAVBOX in a fully open state (85-100%) under the condition that the system meets the requirements of indoor load changes to keep the system static pressure to the bottom.
Total air volume control: Its working principle is to let the VAV BOX controller adjust the air volume at the end to meet the load requirements according to the indoor load changes, and transmit the air volume signal to the inverter controller. The inverter controller collects the air volume of each terminal within its jurisdiction, performs decoupling analysis and calculation, and then accumulates it to control the inverter and adjust the motor speed of the air conditioner so that the air supply volume is equal to the sum of the total terminal air volume.
The role of variable air volume control system
The variable air volume system means that the supply air changes with the exhaust air, and the exhaust air changes automatically or artificially according to people’s needs. The supply air and the exhaust air form a dynamic balance, so that the room always maintains a relatively constant temperature and humidity. and slight negative pressure.
Its working principle is that when the exhaust air volume changes, the system end device automatically adjusts the air volume sent into the room to ensure that the indoor temperature, humidity and pressure are kept within the design range, so that the air supply volume of the air handling unit at low load decreases. , the speed of the blower of the air handling unit is also reduced to achieve the purpose of energy saving.
The VAV damper contains an averaging airflow measurement probe, airflow controller and actuator. Airflow is controlled based on actual flow measurement by changing the damper blade position. Flow control damper maintains the required airflow independent of duct pressure variation. Airflow control damper is available in several versions. The blade gasket enables airtight shut-off operation, and external insulation is used to attenuate radiated sound into the space.
VAV Damper Advantages
Made of PP plastic insulation, anti-corrosion Intelligent and precise air volume control Energy saving control Wide range of applications Specifications can be customized on demand
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.
With the continuous expansion of the application range of plastic dampers, the role played by valve accessories in the application scenarios cannot be underestimated. Once the plastic dampers in normal operation have abnormal conditions, it will bring a lot to the production process of the application scenarios. The impact is precisely because so many users who purchase plastic air valves are extremely concerned about the problems related to the use of air valves. So what issues should be paid attention to when using plastic air valves? The following is a summary of the details that need to be paid attention to when using plastic air valves:
First of all, pay attention to the problem of protecting the outer surface of the damper
It is difficult to distinguish PP plastic air valve from ordinary valves only from the working principle and appearance structure of PP plastic air valve, but the plastic air valve can be distinguished well according to the different materials of manufacture. If the outer surface of the air valve is damaged or worn, it may affect its excellent use effect. Therefore, when using the plastic air valve, the outer surface of the air valve must be protected in place to avoid damage to the outer surface. To the normal production of the enterprise.
Secondly, the environment around the application scene should be controlled in a state suitable for the operation of the air valve
Combining many cases of using polypropylene plastic air valve, it can be found that the simple structure of the air valve actually has high requirements for the environmental conditions of the application scene. If an index in the application scene exceeds the index suitable for the normal operation of the air valve It may cause damage to the air valve. Therefore, even if the price of plastic air valves purchased in large quantities is favorable, we must strictly monitor the surrounding environmental conditions, and try to control all the indicators in the environment where the air valve is located in a state that can play a good use effect.
The above summary of several issues that need to be paid attention to when using PP plastic air valves is here for the time being. I have to admit that with the assistance of plastic air valves, the media flow in many application scenarios has become more controllable, so when companies use polypropylene plastic air valves, they must pay more attention to these details and strive to make the air valve fully functional. The desired effect.
XIXHENG EP LTD specializes in the production of PP plastic pneumatic dampers. The material is PP polypropylene. It is suitable for ventilation systems with explosion-proof requirements such as chemical industry and laboratories. PP plastic pneumatic dampers are composed of plastic dampers and pneumatic actuators. The size supports customization , square or round
XICHENG ER LTD specializes in the production of PP plastic pneumatic dampers. The material is PP polypropylene, which is resistant to acid and alkali corrosion. The working principle of PP plastic pneumatic dampers is the same as that of PP electric dampers, but the electric actuator is changed to a pneumatic actuator. The third-party plate solenoid valve controls the switch of the air pipe to realize the opening and closing of the PP plastic pneumatic air valve.
PP plastic pneumatic air valve is suitable for application environments with explosion-proof requirements such as chemical plants and laboratories. It is used in PP material ventilation duct systems, and is connected to PP air ducts. It is used for exhaust control of corrosive gases, anti-corrosion and acid resistance. Alkali, PP plastic pneumatic air valve has complete specifications, and is used with PP air pipe, elbow, tee, and reducing diameter to form a complete PP ventilation pipeline system. The pneumatic actuator of PP plastic pneumatic air valve can be selected according to the specifications of the air valve. torque.
PP plastic pneumatic air valve is a kind of non-sealed butterfly valve, which is widely used in colleges and universities, chemical industry, biology, electric power, energy, environmental engineering, etc. in the production process, the medium temperature is less than or equal to 90℃, and the nominal pressure is less than 0.1Mpa. Connecting, opening and closing or adjusting the medium, it is usually installed on the top of the fume hood, the PP suction hood and the inlet of the pipeline of the one-use-one-standby spray tower to switch the exhaust gas flow direction of the spray tower.
PP plastic pneumatic air valve principle
The PP plastic pneumatic air valve is installed in the PP pipeline system, and the PP pneumatic air valve can be opened and closed according to the needs through manual operation or PLC automatic control technology. , Drive the rotation of the butterfly valve blade, achieve a 90-degree angle, achieve the purpose of opening and closing, and have a feedback indication function. Through the differential pressure detection device, after closing the air valve, the signal is transmitted to the PLC system, so as to control the PP fan inverter to reduce the speed and save energy.
PP plastic pneumatic air valve performance characteristics
PP material processing, acid and alkali corrosion resistance, strong anti-corrosion performance; PP pneumatic air valve has socket design at both ends, and can also be welded flange connection; High-strength actuator, all-copper design, switch life more than 20,000 times; The inner and outer walls are smooth and the wind resistance is small.
PP plastic pneumatic damper industry application
Workshop ventilation system Chemical fresh air system Laboratory ventilation system HVAC system
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.
