FAQ

The design objective of the closed valve is to achieve full open, full close, and airtight isolation. The soft seal ring is pressed against the seat when closed and detaches from the seat when open. If it is left in the intermediate position for long-term adjustment, the seal ring will be continuously eroded by high-speed airflow accompanied by vibration wear, and the valve disc's pulsation at small openings will also damage the sealing surface and clamping mechanism, leading to increased air leakage when fully closed and reduced seal life. For pipe sections requiring frequent air volume adjustment, analog control valves should be selected, and closed valves should be installed separately at isolation points to perform their respective functions. In practical engineering, regulating valves and closed valves are often arranged in series. The regulating valve is responsible for daily air volume balance, while the closed valve only operates during maintenance or shutdown. This approach ensures both adjustment accuracy and protects the closed valve's sealing components, avoiding premature failure of a single valve being used for two different operating conditions.

Miter joints are typically made with socket connections. After inserting the duct into the socket, use weld electrodes of the same material to perform circumferential sealing along the joint. Alternatively, add bolts at the socket and pair them with sealant for fastening. This method offers quick installation and excellent sealing, making it suitable for fixed pipe sections. For locations requiring frequent disassembly for maintenance or connections to equipment,Flange connection (flange connection) is recommended. Both ends of the miter joint are equipped with flange edges, which connect to the duct or equipment flanges using bolts and gaskets for easy assembly and disassembly. Socket welding is cost-effective and airtight, while Flange connection provides flexibility and facilitates replacement. Choose the appropriate method based on the specific application. Regardless of the connection method used, inspect the joint for tightness and proper alignment after installation to prevent corrosive gas leakage. Negative-pressure pipe sections, in particular, must ensure continuous welds and intact gaskets. Post-installation, integrate system air leakage testing to verify the integrity of the connections.

Tiered Troubleshooting: First, confirm whether the actual airflow exceeds the design value. Excessive gas velocity may cause liquid droplets to fail to separate or even lead to secondary entrainment. Reduce the airflow or increase the demisting section. Check if the baffle spacing is too large, the installation direction is incorrect, or the packing is improperly installed, causing short circuits. Verify if the liquid droplets are too fine and exceed the current internals' collection range, considering switching to packed or two-stage combined demisters. Inspect if the flushing water is excessive or if the liquid seal drain pipe is blocked, resulting in water accumulation inside the box. Adjust the airflow, reinstall the internals, increase the number of demisting stages, or switch to denser water collection plates to address the water carryover issue, which typically resolves the problem.

Flange leakage is typically caused by gasket aging, bolt loosening, flange face misalignment, or seal surface damage. First, check if the bolts are tightened evenly in a diagonal sequence. Bolts may loosen due to thermal expansion and contraction of pipelines and operational vibration. Re-tightening them according to specifications can eliminate most leaks. If leakage persists, shut down and relieve pressure, then disassemble the flange to inspect if the gasket is damaged, misaligned, or aged. Replace the new gasket and re-center the installation. For warped or deformed flange faces or scratched seal surfaces, the flange needs to be replaced or the seal surface machined. Do not excessively increase bolt torque to force a seal, as this may crack the plastic flange. Establishing records for bolt tightening and gasket replacement during routine maintenance can effectively reduce repetitive leaks.

Cannot be simply interchanged. Switching actuators do not have servo control circuits internally and can only be fully open or fully closed, unable to stably hold a mid-position; they will frequently operate and fail to position accurately in variable air volume control applications. Adjustment-type actuators can be used as switching actuators, but at a higher cost. Spring-return type and standard type actuators have different power-off behaviors and cannot be arbitrarily replaced. When replacing actuators, maintain consistency in control method, voltage, torque, travel time, signal format, and reset method, otherwise it may cause control failure or loss of safety functions.

When the fan noise is primarily in the medium-to-high frequency range, a conventional cylindrical reactive muffler can suffice; when the noise spectrum features prominent low-frequency components, noticeable fan pulsation noise, or when simply extending a reactive muffler does not meet low-frequency requirements, an impedance Composite (impedance Composite ) muffler should be selected, utilizing expansion chambers and resonance chambers to target low-to-medium frequency noise attenuation. Centrifugal fans, positive displacement fans, and high-pressure systems often exhibit significant low-frequency noise. The most prudent approach is to first measure the fan noise octave band spectrum and determine the reactive and resistive section configurations based on the required noise attenuation for each frequency band, avoiding Blindly extending (blindly extending) the reactive section.

The load-bearing capacity of grating plate is related to the plate thickness, the structure and orientation of the reinforcement bars, the support span, and the wet weight of the fill material. Injection molded grating plate can bear the weight of conventional bulk fill material and liquid weight within a reasonable spacing of support rings and beams. For large-diameter towers, the load-bearing capacity is ensured by densifying support beams, increasing segments, and reducing the span of individual plates. In design, the total load should be calculated based on the fill material's bulk density, loading height, liquid volume, and potential maintenance loads, and then the plate thickness, reinforcement bars, and support spacing should be determined accordingly. The span of grating plate should not be excessively large without intermediate support, otherwise, long-term loading may cause deflection, deformation, or even detachment. When selecting, prioritize plates with rationally arranged reinforcement bars and solid molding. For conditions with high liquid volume and loading height, the spacing of support beams should be appropriately densified.

It is not absolutely constant but maintains airflow within an allowable deviation range under specified working differential pressure. Venturi valves have applicable upper and lower limits of differential pressure: when the differential pressure is below the lower limit, the spring pushes the valve core to its maximum opening but still fails to maintain airflow; when the differential pressure exceeds the upper limit, the valve core closes to its minimum position but cannot fully compensate, and airflow will still vary outside the working range. When selecting, ensure that the differential pressure across the valve before and after normal system operation falls within the working range. Consider pressure changes caused by fan frequency variation and filter blockage, and have the design personnel verify if necessary.

The cabinet body and lining of the PP fume hood are made of polypropylene, which is resistant to acid, alkali, and salt corrosion, does not rust, and is suitable for laboratories that frequently use hydrochloric acid, nitric acid, sulfuric acid, alkaline solutions, and corrosive gases in chemical, electroplating, and semiconductor fields. The all-steel fume hood has high strength and good performance in high-temperature and organic solvent resistance, making it suitable for laboratories primarily using organic reagents and high-temperature heating. The surface is treated with anti-corrosion coating, but its resistance to strong corrosion is inferior to PP. For highly corrosive environments, choose PP; for organic solvents and open flames at high temperatures, select all-steel or stainless steel. When the medium is complex, specify the commonly used reagents to the manufacturer for material selection.

Common reasons include: insufficient circulating caustic soda concentration or long-term non-replacement, leading to saturated absorption capacity; insufficient spray volume, nozzle blockage, or uneven spraying, resulting in dry zones in the packing layer; packing blockage, crystallization, or scaling reducing gas-liquid contact area; airflow exceeding design value, high gas velocity, or insufficient contact time; abnormal demisting and wastewater discharge. Regularly test the circulating liquid's pH and density, promptly replenish alkali and replace water, clean and clear nozzles and packing, and verify if the actual airflow exceeds the design. When the single-stage tower is insufficient for high-concentration exhaust gas, increase the number of spray stages or use two-stage towers in series. Do not rely on indefinitely increasing alkali concentration as a solution.

The travel time of a damper actuator is related to its torque specifications. Low-torque, fast models can complete their full cycle in just seconds, while high-torque models require longer times due to their higher gear reduction ratios. Generally, the greater the torque, the slower the travel time, which is a normal design principle. When selecting, under the condition that torque requirements are met, interlocked and emergency dampers should preferably be chosen with shorter travel models. If an actuator of the same specification operates noticeably slower, it is often due to jamming in the damper shaft seat, valve vane wall friction, excessive sealing pressure, or low power supply voltage. Mechanical load should be checked first instead of assuming actuator failure.

Torque depends on the wind area of the valve vane, the pressure difference before and after the valve, the friction resistance between the vane and the shaft seat, the sealing pressure, and the safety factor. Generally, larger diameters, higher wind speed and wind pressure, and more vanes require greater torque; soft-sealing valves need to overcome the sealing ring pressure, and multi-leaf valves need to sum the torque of each blade. The simplest and most reliable method is to provide the valve diameter, type (round valve or multi-leaf valve), wind pressure, and medium to the valve manufacturer, who will select and match the complete anti-corrosion actuator based on experience and calculations. When selecting independently, ensure sufficient torque margin, as insufficient torque can lead to failure to operate, stalling, or motor burnout.

Resistive mufflers perform well on mid-to-high frequency noise but have limited effectiveness on low-frequency noise due to the long wavelength of low-frequency sound waves, which are not easily absorbed by conventional thickness acoustic absorption materials. For fan noise dominated by low frequency or high noise reduction requirements, thickening the muffler plates, increasing the bulk density of the acoustic absorption material, extending the muffler length, or adopting impedance composite mufflers utilizing the reactive principles of expansion chambers and resonance chambers for low-frequency noise reduction can be considered. It is recommended to conduct a noise spectrum test on the fan first and then design the muffler based on the spectrum to avoid selecting based solely on experience.

Spray Tower Accessories Prefer Vertical Tank-Immersion Pumps: They feature no shaft seal, resistance to acid and alkali corrosion and leakage, allow brief dry running, reliable submergence suction, and occupy no floor space, making them ideal for unattended continuous operation of exhaust towers. The advantage of horizontal corrosion-resistant pumps is the convenience of ground-level maintenance during repairs without lifting, suitable for applications where tank tops cannot be opened, high pump power is required, or ground-level maintenance is the local practice. Selection should consider tank structure, site conditions, medium temperature, and maintenance requirements. In cases with strong corrosion and concerns about seal leakage, vertical shaftless pumps are more reliable.

Displacement control (also known as window opening control) indirectly calculates the required air volume based on the window opening, offering fast response and lower cost. However, it assumes that the face velocity is solely related to the window opening and cannot compensate for air volume changes caused by factors such as filter blockage or fan aging. Face velocity control directly installs a face velocity sensor at the window for closed-loop regulation based on actual face velocity, providing more direct and higher safety control. However, the sensor is located in the contaminated area, requiring regular cleaning and calibration. High-standard laboratories can adopt face velocity control or a combination of displacement control with air volume measurement, with the specific choice determined based on safety level and budget.

The activated carbon adsorption tower is primarily used to treat various organic waste gases and odors, such as benzene, toluene, xylene, and other aromatic compounds, aldehydes, ketones, esters, and other organic volatile organic compounds (VOCs), as well as odorous waste gases generated in industries like food processing and wastewater treatment. For acidic or alkaline waste gases and those with high dust content, it is recommended to install a spray tower for pretreatment before the activated carbon tower to remove acidic or alkaline components and particulate matter, preventing pore blockage of the activated carbon and extending its service life. For high-concentration organic waste gases, it is recommended to adopt a combination of processes such as rotary concentrator or catalytic combustion for treatment.

Both are wet exhaust gas purification equipment, but their internal structures and applicable conditions differ. Standard spray towers rely on a packing layer to increase gas-liquid contact area, suitable for conventional acid-base waste gas and acid mist treatment, but viscous waste gas and dust can easily cause packing blockage. Cyclone towers utilize centrifugal separation generated by multi-layer swirling vanes and liquid film adhesion to remove dust, making them more suitable for viscous exhaust gas such as paint mist and conditions with higher dust content, and less prone to blockage. Cyclone towers have relatively higher resistance, requiring matching fans with higher pressure when selecting.

The main differences lie in the manufacturing process and applicable scenarios. Formed ducts are produced using an extrusion process, resulting in uniform wall thickness, smooth inner surfaces, low air resistance, and high production efficiency, making them suitable for standard specifications and large-volume production. Machined ducts are fabricated from PP flame-retardant sheets through welding, with flange reinforcement, making them ideal for large diameters, non-standard dimensions, and special-shaped ducts. They offer high flexibility but relatively lower production efficiency. Both materials are corrosion-resistant and acid/alkali-resistant. Standard branch ducts are recommended for formed ducts, while large-diameter main pipelines are suitable for machined ducts.

The PP elbow is primarily designed for spigot connection, where the spigot end of the elbow is inserted into the end of the PP ductwork, or the ductwork is inserted into the spigot of the elbow. It is sealed with sealant or a seal ring, offering easy and flexible installation, suitable for small and medium pipe diameters. For large-diameter pipelines, the flange connection method can be used. Flange plates are welded to both ends of the elbow, and the ductwork flanges are connected with bolts and sealed with gaskets, providing excellent sealing performance and secure connections. During installation, ensure proper insertion and good sealing to prevent exhaust leakage. The specific connection method should be selected based on the pipe diameter and pressure.