FAQ

Variable Air Volume (VAV) fume hoods require the exhaust airflow to be automatically adjusted when the door opening varies, while maintaining a constant face velocity. This necessitates the use of analog electric regulating dampers. The actuator receives standard electrical signals from the controller, continuously adjusts the vane angle, and feeds back the actual vane position to the control system, forming a closed-loop control. Standard on/off electric valves can only be fully open or fully closed, and manual valves require manual adjustment, neither of which meets the requirements for real-time, continuous regulation. Constant Air Volume (CAV) fume hoods or conventional exhaust hoods can be balanced once using manual multi-leaf dampers. Whether to use automatic dampers depends on the control method of the ventilation system. When a laboratory has multiple VAV fume hoods, it is common to install one analog valve per hood outlet, with the building management system centrally managing the fan frequency conversion and airflow balancing.

For standard electric actuators, after power failure, the valve remains in the position at the moment of power interruption and will not automatically open or close. When power is restored, it continues to operate according to the control signal. If the process requires the valve to automatically open during power failure (e.g., emergency ventilation, ensuring air circulation) or automatically close (e.g., preventing gas backflow, isolating equipment), a spring-return actuator should be selected: when powered, the motor overcomes the spring force to maintain the working position, and after power failure, the spring pulls the valve disc to the preset safe position. When ordering, the requirements for the power-off safe position and the return direction must be clearly specified. Standard hold-type and spring-return-type structures and prices differ and cannot be mixed. For high-safety requirement environments, manual reset and position feedback can also be added. During design, the safety strategy after power failure should be considered for each unit to avoid the valve being stuck in the wrong position in case of an accident.

It is not advisable to make the transition section too short. The shorter the diameter change section, the larger the cone angle, especially during gradual expansion, where airflow is prone to detaching from the cone wall, forming a vortex zone, significantly increasing resistance and noise. An excessively short reducing adapter approaches a sudden expansion, losing the significance of smooth transition. The gradual expanding reducing adapter should control the expansion angle and ensure sufficient length to gradually decelerate the airflow along the cone wall. The cone angle of the gradual converging reducing adapter can be slightly larger, and the length can be appropriately shortened. The reasonable length balances material savings and resistance control. It can be calculated based on the diameter difference between the two ends and the recommended cone angle, rather than being arbitrarily determined based on installation clearance. When space is indeed limited, segmented diameter changes or flow-directing structures can be added at the transition points. Design priority should be given to ensuring the transition length at critical areas such as fan inlets and outlets, which significantly reduces fan energy consumption and vibration impact.

The selection criteria mainly include joint clearance, plate thickness, and bevel type. For thin plate ducts with small gaps, fine round welding electrodes are typically used for root welding, followed by slightly thicker round electrodes for cover welding, resulting in smooth welds and reduced material consumption. For thick plates, after V-shaped beveling, round electrodes are used for root welding to ensure full penetration. The fill and cover layers are more efficient with triangular electrodes, as their triangular cross-section provides a larger contact area with the bevel, fewer fill layers, and a fuller weld profile. Double-bead electrodes have high deposition rates, making them suitable for large-area thick plate seams and longitudinal joints of cylinders, but they require higher welding torch power and more skilled welder techniques. When purchasing, match fine round, thick round, and triangular electrodes according to common plate thicknesses, using round electrodes for corners and roots, and triangular electrodes for large bevels. Weld electrode specifications must correspond to the welding torch nozzle diameter; mismatched specifications will affect wire feeding and fusion.

Interlocks prevent fans from starting under closed duct conditions, which can cause pressure buildup, current overload, duct collapse, and equipment damage. They also automatically close valves after fan shutdown to prevent outdoor air from infiltrating, corrosive gases from spreading in the workshop, and cold air from entering pipelines and rooms during winter. The standard interlock sequence is to open valves first during startup, then start the fan upon receiving the "fully open" signal, and to stop the fan first during shutdown, followed by delayed valve closure. When multiple branches share a fan, the control system opens the corresponding branch valves based on the number of operating units and required airflow, and may adjust fan frequency control as needed. Interlock logic is implemented by relays or programmable controllers in the control cabinet, with valve position feedback and fault alarms configured. Valve-to-fan interlocking is a fundamental requirement for exhaust automation, and the commissioning process must verify the sequence of valve opening, fan startup, fan shutdown, and valve closure, as well as timeout protection for each step.

Properly installed ring flanges with spigot welding will not leak air. The key lies in ensuring the two ends of the ducts are inserted correctly and the axes are aligned. The annular gap of the socket should be continuously welded around using a weld wire of the same material, without any breaks, pores, or incomplete welds. Before welding, clean the oil and oxide layers from the socket. During welding, ensure the weld wire fully fuses with the base material, and no stress should be applied to the weld before it cools. For systems with high sealing requirements, air leakage tests or segmented pressure checks can be conducted after welding. Air leakage typically occurs when the weld is not closed, the weld wire does not fully fuse with the base material, or the socket is not inserted properly. These are all construction quality issues. As long as the connection is properly inserted according to the process, fully welded around the circumference, and post-weld checks are performed, the sealing performance of the ring flange joint can meet the requirements of corrosion-resistant ventilation systems.

Poor electrode adhesion is usually caused by cold soldering, common reasons include low temperature, gun movement too fast, seams not cleaned properly, or insufficient electrode pressure. First confirm the gun temperature reaches PP melting requirements, remove oxidation and contaminants from the seam surface with a scraper before welding, ensure the electrode and base material show a molten glow simultaneously during welding, keep the electrode perpendicular to the weld and apply stable pressure. Test weld with scrap material before actual welding, after cooling, forcefully peel the weld to check, a well-fused weld should not tear along the joint surface.

The standard manual air damper is primarily used for air volume regulation. There is a clearance between the damper blade and the body, resulting in a certain amount of air leakage even when fully closed, making it unsuitable for complete replacement of airtight dampers. In applications requiring high closing airtightness, for maintenance isolation, or to prevent gas backflow, it is recommended to select airtight dampers with soft sealing strips on the blade edge or specialized airtight dampers. While general air volume balancing allows for a small amount of air leakage, applications such as maintenance isolation, preventing gas backflow, and hazardous material ventilation demand higher closing tightness. When selecting, it is essential to distinguish between regulating dampers and airtight dampers, as standard regulating dampers should not be used for isolation tasks. When closed, airtight dampers compress the soft sealing strip against the seat, resulting in significantly less air leakage compared to standard dampers, with corresponding increases in price and operating torque.

Window air leakage is usually caused by aging of the sealing strip, loose fastening screws, or deformation of the viewing panel. First, re-tighten the screws in a diagonal order to ensure even pressure distribution on the cover, and observe if the air leakage is eliminated. If the leakage persists, shut down the machine and release pressure, then disassemble the window to check if the sealing strip has lost elasticity, been corroded, or has joint gaps. Clean the sealing surface, replace the new sealing strip, and reassemble it. Deformed, warped, or cracked viewing panels must be replaced in their entirety and cannot be used Struggle . During installation, the sealing strip must be continuous, smooth, and tightly sealed at joints. Ensure uniform screw torque to avoid uneven tightening or excessive force that could crack the panel. After assembly, perform an air leakage check, and conduct a follow-up inspection during operation. Regular inspections should focus on detecting crystallization, leakage, and loose screws around the window. Address any issues promptly to maintain long-term sealing performance.

The valve disc, in low airflow or fluctuating conditions, may remain partially open, repeatedly lifted and dropped by airflow striking the seat, generating noise and wear. Common in low-load fan operation, fluctuating multi-fan parallel conditions, or excessively light valve disc or improper positioning. It can be eliminated by adjusting fan operating conditions to maintain stable airflow, selecting check valves with damping buffers, or adjusting valve disc weight or positioning. Systems with variable frequency low-speed fan operation require particular attention to valve disc stability, and electric interlock valves may be used if necessary.

Manual hermetic valves require not only rotating the valve disc to the fully closed position but also continuing to operate the handle to complete the eccentric or four-bar pressing action and lock it, ensuring the seal ring is uniformly pressed against the valve seat in a circular pattern to achieve a reliable seal. If leakage persists after tightening, check whether the seal ring is aging or deforming, or if it is obstructed by foreign objects; whether the valve seat is deformed; whether the valve disc compression stroke is properly positioned; and whether the valve shaft is securely fastened. Before closing, clean the dust, crystals, and debris from the valve disc and valve seat. Fine particles trapped on the sealing surface can cause localized gaps and air leakage, which is a common issue on-site. After treatment, repeatedly open and close the valve a few times to verify the seal. Replace the seal ring promptly if it shows indentations, hardening, or cracks. During installation, ensure the valve body is coaxial with the pipeline and that the flanges are evenly loaded to prevent valve seat deformation, which could affect the seal.

Under the same specifications and loading conditions, the structured packing has a more complex configuration, typically featuring a higher specific surface area and voidage, leading to more thorough gas-liquid contact and higher efficiency, but at a slightly higher price. The Raschig ring, on the other hand, has a simpler structure, high throughput, strong anti-blocking and anti-fouling capabilities, is cost-effective, and has low replacement costs. When the gas is dirty, contains solid or viscous substances, or when economic reliability is prioritized, Raschig rings are often used with appropriately increased specifications. For cleaner gas requiring higher purification efficiency, structured packing can be employed to enhance mass transfer performance. The two types of packing can also be combined in layers within the same tower: the lower section near the inlet uses large-scale anti-blocking packing, while the upper section employs high-efficiency packing for fine treatment, balancing anti-blocking and efficiency. Actual performance also depends on spray distribution, packing height, and gas-liquid ratio. Selection should be based on pollutant concentration and compliance requirements, with reference to similar project packing configurations when necessary.

The footrest is an elevated working surface, with drain holes on the plate surface allowing spilled chemicals and rinse water to drain quickly below the plate. The ground should be equipped with anti-corrosion flooring and diversion channels to direct the liquid to collection tanks or wastewater treatment systems, achieving dry-wet separation and clean-pollution diversion. The footrest only addresses anti-slip, anti-corrosion, and leakage issues on the working surface and cannot replace ground corrosion protection and waste liquid collection facilities. During design, ensure smooth integration of plate perforations, ground slope, and diversion channels to prevent liquid accumulation on the plate or ground. Regularly clean the area below the plate, supports, and diversion channels to remove accumulated chemicals and sludge, preventing liquid buildup that could corrode supports and flooring. Promptly repair and clear any damaged flooring or blocked diversion channels to establish a complete path for plate leakage, ground collection, and centralized treatment, avoiding chemical overflow that causes corrosion and safety hazards.

The large valve disc has a wide wind-receiving area and significant aerodynamic torque, making manual operation with the handle very labor-intensive. It should be equipped with a worm gear reducer, allowing the valve disc to be rotated with minimal torque using the handwheel. The worm gear also features self-locking functionality to prevent the valve disc from being moved back by airflow. If the valve still sticks after installing the worm gear, check whether the valve shaft and shaft seat are concentric, whether the bearings are contaminated with dust or crystallized, and whether the valve disc is deformed by heat, causing wall friction. Clean the crystallization, correct the concentricity, and apply lubricant. Avoid using a force pipe to hard turn the handle, as this may break the valve shaft, damage the worm gear, or deform the valve disc. For large-diameter valves, inspect the welds of the valve disc reinforcement and shaft seat for cracks. After treatment, perform several full open/close cycles to ensure uniform torque. If necessary, the manufacturer should verify whether the actuator torque matches the requirements. Valves that have been stuck for a long time should have their bearings replaced or undergo overall maintenance.

Leaf valve leaf synchronization issues are typically caused by loose or Detachment of the coupling pin in the linkage rod, or loose of the crank fixing screw, resulting in some valve leaves not rotating with the main shaft. The machine should be shut down to inspect the linkage rod, crank, and pins. Worn pins should be tightened or replaced, and the fixing screws should be locked. All valve leaves should be manually adjusted to the same angle and the linkage rod repositioned. After the treatment, perform several full-cycle openings and closings to observe whether all leaves open and close consistently, without delay or jamming. During routine inspections, pay attention to the consistency of the opening, ensure the linkage mechanism is not jammed by debris or crystallization, and maintain cleanliness at the pin locations. In corrosive environments, promptly replace rusted metal linkage components or select cranks with corrosion-coated covers. After adjusting the synchronization mechanism, mark it for future reference to check for displacement.

Depends on the total torque of the vane assembly. The aerodynamic torque of each vane in the multi-vane valve is Summary ed to the active vane shaft via linkages; the larger the cross-section, the more vanes, and the higher the wind speed, the greater the total torque. If the total torque falls within the rated torque range of a single actuator with a margin, one actuator is sufficient; for excessive torque, a high-torque actuator can be selected, or the valve can be divided into two groups, each equipped with one actuator for synchronized control. When selecting, provide the cross-sectional dimensions and wind pressure; the manufacturer calculates the torque, and actuators should not be matched based solely on experience with small valves.

It is generally not recommended to mix acidic and alkaline exhaust gases in the same tower for simultaneous treatment, as the absorbent can only maintain one pH level, and certain gas mixtures pose safety risks. For example, mixing cyanide-containing exhaust with acidic gases may produce highly toxic hydrogen cyanide gas, while ammonia mixing with acid mist can form ammonium salt crystals that block the system. The correct approach is to separately collect, transport via dedicated pipelines, and treat acidic, alkaline, cyanide-containing, and organic exhaust gases in individual towers, each using the corresponding absorbent. Shared equipment can only be considered when the components are compatible and the process allows for alternating operation. Specific requirements must be determined by process design in accordance with safety regulations.

The transition section length must ensure a smooth conversion from square to circular twisted surface, while also meeting the requirements for gradual expansion and contraction angles to avoid flow separation at sharp turns. If the transition section is too short, the twisted surface becomes abrupt, leading to increased flow vortices and resistance, and may also cause vibration and noise in the flat section under negative pressure. If it's too long, it results in material waste and occupies more installation space. Generally, the appropriate length is determined based on the rectangle's longer side dimension, the circular end diameter, and the area difference between the two ends to ensure a smooth twisted and conical surface. The square-to-round transition at the fan inlet must particularly guarantee uniform airflow into the impeller. When necessary, refer to the fan manufacturer's connection requirements and recommended length for design. In space-constrained situations, it can be shortened appropriately, but the resistance should be checked and stiffeners added to the flat section to prevent resonance.

The multi-sphere balls are spherical and lightweight. Under high gas velocity, especially during fan startup, valve sudden opening, or load fluctuation, the upper spheres in the bed may be lifted, rolled, or fluidized by the airflow, leading to long-term wear and carryover. Therefore, the design requires controlling the empty tower gas velocity within the allowable range of the packing and not exceeding the fluidization point gas velocity of the packing. Pressure plates, pressure grids, or limiting gratings should be installed above the packing layer to confine the balls within the bed. During fan startup, the air damper should be closed slightly, and the air volume should be adjusted slowly to avoid instantaneous airflow impact on the bed. Avoid frequent and large load fluctuations during operation. A small clearance should be left between the pressure plate and the packing to limit the upward floating without crushing the balls. If balls are still carried into the demisting section, review whether the air volume exceeds the standard or the pressure plate gap is too large, and supplement a pressure grid above.

Both can support fillers, but their structures and applications differ. The integral grating plate is a standard injection molded part with high hole rate, light self-weight, quick assembly, and low cost, making it suitable for supporting large-particle bulk fillers under standard tower diameters, with easy batch supply and replacement. The porous plate is punched from a whole plate, allowing the hole size to be made very small, and the hole type and open area rate can be customized, making it suitable for supporting fine-particle filter media, activated carbon, as well as for airflow equalization plates, screening plates, or used in non-standard sizes and irregular spaces. For large-particle fillers and conventional towers, the grating plate is more economical; for fine-particle filter media, gas-liquid equal distribution, and solid-liquid screening, the porous plate is more appropriate. The two can also be used together, for example, the grating plate supporting the main filler with an additional porous equalization plate above. When uncertain, calculate separately based on the minimum filler size and tower diameter to quickly determine the solution.