FAQ

When dusty or liquid-containing airflow changes direction, particles and droplets are easily thrown to the outer side of the elbow due to inertia and adhere to it. Liquid and mud may also accumulate at the bottom of the horizontal elbow. When handling dusty, sticky, or liquid-containing gases, inspection ports or drain ports can be installed on the outer wall and bottom of the elbow to facilitate regular cleaning. The design of the internal pipe velocity should not be too low to maintain a certain self-cleaning ability and reduce particle sedimentation. The plastic inner wall is smooth, with lower adhesion for debris compared to metal, but regular inspection should still be conducted during maintenance to check for fouling and wear on the elbow. Accumulated dust and liquid should be cleaned promptly, and it is necessary to verify whether the drain port is unobstructed and whether the elbow orientation is reasonable. Elbows near dust sources and mist segments can have their outer walls thickened or be made of wear-resistant materials to extend service life.

First, calculate the required cross-sectional area based on the exhaust airflow and the recommended internal pipe velocity. Then, determine the length and width of the rectangle by considering the ceiling height, clear space under the beam, and equipment interface. The aspect ratio of the rectangle should not be too high. A excessively flat square pipe has more dead zones at the corners, higher resistance, and is prone to vibration on the plate surface. Generally, the aspect ratio is kept within a reasonable range to avoid being overly flat and narrow. After determining the cross-section, verify the plate thickness and stiffener spacing based on the fan negative pressure to ensure the strength and stiffness of the wall plate. Laboratory fume hoods also require compliance with face velocity control and variable air volume systems' demands for pipeline tightness and response speed. When necessary, the ventilation department should uniformly calculate the cross-sectional areas of each section. Once the cross-section is determined, minimize the number of specifications to facilitate processing, standardize support and suspension brackets, and streamline spare parts for later use.

The two products serve different functions and are used in series. The flame-retardant square damper is responsible for daily airflow regulation and is made of self-extinguishing material. The fire-rated damper is installed at air duct penetrations through fire compartments, floors, and machine rooms, and is controlled to close by temperature-sensitive melting or electrical signals, featuring fire resistance and smoke prevention functions. In laboratory exhaust systems, flame-retardant regulating dampers are installed at the outlets of fume hoods, and fire-rated dampers are installed at fire compartment penetrations. Flanges are used for reliable connections between plastic ducts and fire dampers, with fireproof sealing applied. The locations of penetrations and the number of dampers are determined according to building fire protection design, and the installation is included in fire inspection after construction.

Actuator is installed externally on the valve body, not contacting the pipeline gas under normal conditions, but corrosive gas may diffuse to the actuator when valve shaft seal fails or flange leaks, and strong acid/alkali environment will corrode the metal casing and bracket of the actuator. Ensure reliable valve shaft seal and leak-free pipeline flanges, select actuators with appropriate protection level and anti-corrosion coating according to environment, plastic casings or anti-corrosion covers can be selected for highly corrosive workshops. Seal cable inlet properly to prevent corrosive gas and moisture from entering the junction box.

To reduce the resistance of diameter change, it is essential to ensure the length of the diameter change section and a reasonable cone angle. The gradually expanding section should be particularly smooth to avoid flow separation and the formation of eddies. The welds on the inner wall of the reducer should be polished to reduce protrusions and steps, ensuring the flow of air along the wall is smooth. Attention should be paid to the uniformity and symmetry of the airflow at the impeller inlet during the diameter change. If necessary, guide vanes should be added on the larger diameter side to prevent skewed flow and eddies. Avoid placing elbows or valves, which are disturbing components, immediately after the reducer. Leave a section of straight pipe to allow the airflow to stabilize before turning or adjusting. Well-designed gradually converging and diverging diameter changes have low resistance, but resistance issues often arise from excessive cone angles, incorrect installation direction, or skewed airflow after the diameter change. During system commissioning, if the resistance of the fan section is abnormal, focus on inspecting the length of the diameter change section, the direction, and the arrangement of adjacent pipe components.

The PP welding electrodes exhibit stable chemical properties. They should be stored in a cool, dry environment, away from open flames and oil stains, in sealed packaging. They have a long shelf life and can be used for several years under normal storage conditions. For electrodes stored for an extended period, check for moisture, contamination, or brittleness before use. If the surface is dusty or oily, clean it thoroughly and perform a trial weld. If the fusion is good, the electrode can be used. Electrodes that are noticeably yellowed, brittle, break easily upon bending, or have surface powdering indicate aging. After deposition, their strength decreases, making them unsuitable for pressure-bearing and sealing joints. Electrodes should not be exposed to prolonged sunlight, as ultraviolet rays and high temperatures accelerate the aging of polypropylene. They should also not be stored mixed with solvents or oil stains. Stocked electrodes should be used on a first-in, first-out basis. Long-term inventory quantities should not be excessively large, and high-priority joints should be prioritized for use with new, well-maintained electrodes.

A standard switch valve has a designed gap between the valve disc and body, allowing a small amount of air leakage when fully closed. This is sufficient for general isolation and preventing backflow, which is a normal characteristic of regulating valves. For applications requiring high gas tightness, such as isolating hazardous gases, preventing cross-contamination, or laboratory pressure differential control, select an electrically actuated closed valve with a soft seal on the valve disc edge and an actuator with sufficient closing torque. If air leakage suddenly increases during use, check in the following order: whether the valve disc is fully closed, whether the limit and stroke are correct, whether the seal is damaged, whether the valve shaft connection is slipping, and whether there are foreign objects blocking inside the valve body. After identifying the cause, clean, adjust, or replace the seals. Do not rely solely on increasing the actuator torque to force it closed. Regularly inspect the seals and valve position during fan maintenance to ensure gas tightness during isolation.

The sleeve is a fixed joint for spigot welding, non-removable after welding, with a simple structure and low cost, used for extending and splicing large-diameter ventilation straight pipes. The slip joint consists of a nut and a seal ring, forming a detachable joint that can be sealed by hand or tool tightening without welding, suitable for small-diameter piping requiring frequent disassembly. Ventilation and exhaust pipes generally have large diameters, with welding being the primary method on-site, predominantly using sleeves and flanges; small-diameter water supply, drainage, chemical dosing, and instrumentation piping typically use slip joints. The sleeve excels in reliable sealing and low cost, while the slip joint excels in ease of disassembly. They differ in diameter range and application scenarios. Selection should be based on pipe diameter, the need for frequent disassembly, and connection method, with slip joints generally not used for large-diameter corrosion-resistant exhaust pipes.

The welding site should be well-ventilated to promptly expel the small amount of smoke generated by the heat from the plastic heating. Operators should avoid facing the nozzle's outlet directly and wear protective goggles and heat-resistant gloves when necessary. When in use, the front end of the gun body and the nozzle are very hot and should not be touched by skin or flammable materials. When work is paused, it should be placed on a dedicated stand and should not be placed directly on plates, scaffolding, or flammable materials. After work is completed, power must be turned off, and the gun must be stored only after it has naturally cooled. It is strictly forbidden to place the gun in a box while it is still hot. During confined space and high-altitude operations, power cords must be intact and free of damage and kept away from high-temperature areas. Flammable materials should be cleared below, fire extinguishing equipment should be provided, and measures to prevent burns and fire should be taken. The exterior of the welding machine should be kept dry. During outdoor operations in rainy weather, measures to prevent rain and electrical leakage should be implemented.

Standard manual dampers are equipped with an adjustment screw or positioning gear, which are locked after proper adjustment. Under normal airflow vibration, the opening will not change. If the locking mechanism is loose, the valve shaft clearance is excessive, or the vane is unbalanced with horizontal shaft installation, the vane may slowly return after prolonged vibration, causing airflow drift. After adjustment, confirm that the adjustment screw or gear is effectively locked and mark the handle angle and opening on the valve body or in the records. During routine inspections, verify if the scale matches the adjustment records. If opening drift is detected, re-adjust the airflow and tighten the locking components. For pipe sections with significant vibration, valves with self-locking worm gears can be selected for stronger anti-backflow performance. Regular inspections can also promptly identify vane looseness and shaft sleeve wear, preventing airflow imbalance from being unnoticed for extended periods.

When the tower body is sealed and internally unlit, visibility through the window may be unclear. Corrosion-resistant mirror lights or maintenance lighting can be installed near the window. Light passes through the sight glass into the tower, allowing observation in nighttime and dim environments. Window products with built-in lighting interfaces are also available for selection. For temporary inspections, use a high-intensity flashlight to shine on the sight glass and observe through the opposite window or manhole for better results. When selecting the sight glass, consider its light transmittance. Aging, yellowing, or scratched sight glasses further reduce visibility and should be replaced promptly. Mirror lights and maintenance lighting should be selected with a protection level suitable for corrosive environments. Power supply and wiring must comply with on-site safety requirements. Regularly wiping dust and crystallization from the inner and outer surfaces of the sight glass to maintain cleanliness is the basic measure to ensure clear visibility in nighttime and low-light conditions.

When multiple fans are paralleled and share a common exhaust header, if one fan stops operating without a check valve at the outlet, the airflow from the running fans will short-circuit back through the inactive fan branch, causing system airflow disruption, reverse rotation of the inactive fan, and potentially allowing corrosive gases to enter the workshop through the inactive fan. After installing a check valve at each fan outlet, the running valve is open while the shutdown valve is closed, allowing airflow to move in only one direction towards the header. For critical paralleled systems, an electrically powered sealed valve can be added after the check valve for double isolation during shutdown, preventing short-circuit airflow due to insufficient check valve sealing.

Yes, closed valves are originally designed for long-term isolation, but the seal ring may suffer permanent deformation under prolonged compression, potentially affecting re-sealing. Check the seal ring's rebound after a valve that has been closed for a long time is reopened, and replace it promptly if obvious indentations, hardening, or cracks are found. Spare branch valves are recommended to be operated periodically as part of maintenance cycles to check the mechanism and seal condition. Spare valves in storage should be kept slightly open to avoid prolonged compression of the seal ring.

Before loading, check if the bottom grating plate or porous plate is secure, if the gaps are smaller than the minimum filler size, if the support rings and pressure plates are complete, and ensure the tower is clean of debris. For dry loading, evenly spread the filler from the manhole and spread it in batches to avoid local accumulation and voids. For wet loading, first fill the tower with water to the bed height, then slowly pour the filler to reduce breakage and bridging using the water's cushioning effect, and drain the water after loading. During the loading process, avoid stepping directly on the filler; if entry is necessary, use wooden planks or specialized platforms to distribute weight. After completing the entire layer, level the surface with a rake to ensure uniform height and consistent density, paying close attention to filling near the tower wall to prevent wall flow and gas short-circuiting. Finally, install and secure the upper pressure plate or pressure screen to prevent the filler from being blown or fluidized during operation.

First, confirm whether the anti-slip bumps are leveled by chemical crystallization or dirt. When crystallization and dirt cover the bumps, the anti-slip performance will significantly decrease. It is necessary to rinse and brush them clean with clean water or appropriate cleaning solutions to restore the height of the bumps. If the working surface has long-term oil pollution, the plastic surface will reduce the coefficient of friction when encountering oil, requiring enhanced oil removal and on-site management, as well as timely cleanup of leaks and spills. For areas with higher anti-slip requirements, long-term moisture, or slopes, deeper and denser anti-slip plates can be selected, or anti-slip surfaces and strips can be added to the tread plates. Anti-slip shoes should also be provided for operators. The edges and finishing areas of the tread plates must also be anti-slip and anti-tripping. After treatment, on-site testing should be conducted to determine if the walking friction has improved. If it still does not meet the requirements, replace the tread plates with higher anti-slip ratings for heavy-duty, wet, and slippery areas. Do not continue using smooth plate surfaces with oil or crystallization.

Variable Air Volume Fume Hood System: A standard manual multi-leaf square damper can be installed on the exhaust branch pipe for air volume balancing, and the opening will remain basically fixed after one adjustment. The Variable Air Volume Fume Hood System requires maintaining a constant face velocity when the cabinet door opening changes. An analog electric damper should be equipped at the fume hood outlet, controlled by a face velocity sensor or cabinet door displacement sensor to adjust the actuator and continuously regulate the damper blade opening. Whether an automatic damper is needed depends on the ventilation system type: manual dampers are used for one-time commissioning and balancing, while analog dampers are used for real-time dynamic control. They serve different functions and cannot be mixed. When multiple fume hoods in the same laboratory share a system, each fume hood is typically equipped with one end-of-line control valve, and balancing dampers are installed on the branch pipe. Provide the number of fume hoods, exhaust volume, and face velocity control requirements during selection to ensure the proper matching of manual and automatic dampers.

Interlock the open position signal of each electric square valve with the fan start circuit: after issuing the startup command, open the corresponding electric valve first, then start the fan upon receiving the open position feedback; during shutdown, stop the fan first, then close the valve. When multiple devices share a fan, the control system opens the corresponding branch valves based on the number of operating devices and required airflow, and may link to variable frequency speed regulation when necessary. The interlocking logic is implemented by PLC or relay; it is strictly prohibited to run the fan for extended periods with all valves closed to avoid pressure buildup in the duct that may damage the equipment.

Fog Grid (Dehumidifier) is used to capture and purify liquid droplets carried by the purified gas, returning the droplets to the water tank, protecting downstream fans and ducts, reducing water carryover and chemical loss in the exhaust stack, and is an essential component of wet scrubbers. Removing the fog grid will allow alkaline or acidic liquid droplets to enter the fan, corroding the impeller and ducts, causing fan vibration, and leading to water dripping and white smoke in the exhaust stack. Fog grids are available in baffle and mesh types. Regular cleaning should be performed during operation to prevent blockage, and damaged grids should be replaced promptly. Do not remove the fog grid due to concerns about blockage.

Ideally, the square-end rectangular cross-sectional area should be close to the round-end circular cross-sectional area to ensure the flow velocity remains nearly constant before and after conversion, avoiding abrupt diameter changes while altering the shape. In design, determine the required cross-sectional area based on the processing air volume and recommended flow velocity first, then specify the rectangular length and width and the round pipe diameter to ensure the areas are comparable and the flow velocity remains stable. If limited by equipment interface constraints, resulting in significant area differences between the two ends, extend the transition section for a smooth conversion, or incorporate reducer sections before and after the square-to-round transition to prevent abrupt velocity changes that cause resistance, noise, and vibration. The fan inlet, in particular, must be avoided from experiencing high-speed deflection. During verification, check the flow velocities of both rectangular and circular cross-sections to ensure they fall within the recommended range, adjusting the rectangular length-width ratio or the round-end diameter if necessary.