PP Fire-Resistant Closed-Check Valve

Product Model	PPs soft-sealed fire-resistant check valve
Category	PP Machined Products
Reference Price	Price on request

Hot Customizable for Working Conditions 10 Technical Parameters

Product Overview

The PP Flame-Retardant Closed Check Valve is a self-actuated check valve with a soft seal made of flame-retardant PP material. It functions similarly to a standard PP closed check valve: allowing airflow in only one direction. During fan operation, the positive airflow lifts the valve disc; after shutdown, the disc closes under its own weight and reverse airflow. The soft seal presses against the valve seat to prevent backflow. The difference lies in the valve body, valve disc, and welding rods all being made of flame-retardant PP material, which self-extinguishes upon exposure to fire. It is suitable for corrosion-resistant exhaust systems in indoor, suspended ceiling, and fire-rated environments.

In laboratory, workshop, and pipe well applications, the check valve must be acid/alkali-resistant and flood-proof while maintaining consistent fire performance with the flame-retardant PP duct system. Standard PP check valves are flammable and can become a fire weak point in flame-retardant networks. The PPs Flame-Retardant Check Valve, when paired with flame-retardant ducts and dampers, ensures continuous flame-retardant material throughout the indoor corrosion-resistant exhaust system, meeting both fire and corrosion requirements for indoor corrosion-resistant ventilation projects.

The PP Flame-Retardant Closed Check Valve supplied by Xicheng Environmental Protection features molded or plate-welded PP valve bodies with single or multi-vane swing structures. The valve disc is equipped with a corrosion-resistant soft seal and a limit stop. The valve shaft is horizontally installed, and the valve is available in round, square, and various sizes, compatible with flame-retardant PP ducts. It is a dedicated valve for indoor corrosion-resistant fan outlets and parallel fan duct systems to automatically prevent backflow.

Working Principle

The backflow prevention mechanism of the flame-retardant check valve is self-actuated swing action. When the fan operates, the positive airflow differential pushes the valve disc, which swings around the horizontal valve shaft to a limited angle, allowing airflow. After shutdown, the positive pressure differential disappears, and the valve disc returns to its seated position under its own weight. If reverse airflow exists, the reverse pressure holds the valve disc against the seat, and the soft seal deforms under pressure to seal, preventing reverse airflow. The entire process requires no power or manual intervention and completes instantly upon shutdown.

The flame-retardant performance comes from the flame-retardant components in the PP material. The valve body, valve disc, and welding rods are difficult to sustain combustion upon exposure to open flames and self-extinguish, ensuring the check valve does not become a pathway for fire to spread through indoor ducts. Corrosion resistance maintains the chemical stability of polypropylene against acid, alkali, and salt exhaust gases, preventing rust or jamming of the valve disc and seat in corrosive environments. The soft seal is selected for its corrosion resistance and flame-retardant elasticity, preventing the seal from becoming a double weakness in flame-retardant and corrosion-resistant performance, ensuring long-term flexible operation and tight sealing of the valve disc.

Structural Composition

The flame-retardant closed check valve consists of a PP valve body, flame-retardant valve disc, valve shaft, valve seat, soft seal, limit stop, and end connections. The valve body is a molded cylindrical or plate-welded cylindrical shell with PP flame-retardant welding rods. The valve disc is a PP plate with a corrosion-resistant flame-retardant soft seal embedded at its edge, hinged to the valve body via a horizontal valve shaft for single-direction swing. A flat valve seat is installed at the fully closed position, and an limit stop is set on the opening side.

The valve shaft is made of corrosion-resistant metal or coated material, with a lightweight shaft sleeve at the shaft seat to ensure the valve disc can open with minimal differential pressure. Large-diameter valves use a multi-vane structure to reduce the size and weight of individual vanes, enhancing flexibility in opening and seating. The valve body ends are PP flanges or sockets for connection to flame-retardant ducts. Square check valves are used for rectangular ducts, with multiple vanes arranged in a grid pattern. The valve body is marked with airflow direction and installation orientation, and on-site installation should follow the markings.

Specification Model Table

The following table compares the flame-retardant check valve with a standard check valve for selection based on installation environment.

Item	PPs Flame-Retardant Check Valve	Standard PP Check Valve
Flame-Retardancy	Self-Extinguishing	Non-Flame-Retardant
Corrosion Resistance	Acid/Alkali/Salt Resistant	Acid/Alkali/Salt Resistant
Applicability	Indoor Fire-Rated Environments	Outdoor Open Areas
Compatibility	Flame-Retardant PP Ducts	PP Ducts

Product Features

The PP Flame-Retardant Closed Check Valve integrates flame-retardancy, corrosion resistance, and automatic backflow prevention, serving as a dedicated single-direction valve for indoor corrosion-resistant fan outlets. Key features include:

Full flame-retardant PPs valve body, disc, and welding rods, self-extinguishing upon exposure to fire
Self-opening in the forward direction and self-closing in reverse, requiring no power or operation
Reverse self-tightening soft seal, minimizing leakage during closure
Corrosion-resistant against acid, alkali, and salt, preventing rust or jamming of the valve disc
Compatible with flame-retardant PP ducts for continuous fire performance
Prevents backflow from indoor fans during shutdown and cross-flow in parallel ducts
Available in single/multi-vane, round/square configurations, with customizable diameters

Body Material	PPs Flame Retardant Boards
Welding Rod Material	PPs Flame-Retardant Welding Rod
Sealing Form	Corrosion-Resistant Flame-Retardant Soft Seal Ring
Action Method	Self-Acting Angle Type
Drive Energy	No power required
Valve disc type	Single-petal / Multi-petal
Flame Retardancy	Self-extinguishing
`Corrosion resistance performance`	Acid-alkali-resistant
Connection Method	`Spigot / Flange`
Installation Requirements	Shaft Horizontal

Application Industries

Anti-corrosion fan outlet flame-retardant check valve for laboratory indoor ventilation
PPs exhaust fan anti-backflow valve for suspended ceilings and pipe shafts
Anti-crossflow parallel fan in fireproof compartments of chemical workshops
Anti-corrosion exhaust fan indoor check isolation valve for semiconductor plant
Flame-retardant unidirectional valve for indoor fan outlet in electroplating workshops
PPs exhaust shaft intake check valve for high-rise buildings
Indoor corrosion-resistant fan automatic isolation valve with one primary and one backup

Typical Process Locations

The flame-retardant enclosed check valve is installed on the outlet or exhaust branch pipes of PPs flame-retardant fans in indoor, suspended ceiling, or fireproof compartments. The typical installation is one valve per indoor corrosion-resistant fan outlet. The valve flap opens during fan operation and closes automatically upon shutdown to prevent backflow from exhaust stacks and crossflow among multiple parallel fans. A check valve is also installed at the exhaust shaft intake point for floor exhaust to prevent crossflow between upper and lower floors. The valve connects to PPs flame-retardant ducts via flanges or spigot-and-socket joints, integrating into the entire flame-retardant corrosion-resistant duct system.

Installation requirements are the same as those for standard check valves: horizontal valve shaft, correct airflow direction marking, unobstructed valve flap rotation range, and brackets installed upstream and downstream of the valve. When passing through fireproof compartments, the check valve addresses backflow and material flame retardancy, but fire-rated fire dampers must still be installed separately per fire protection design and cannot be interchanged. Before commissioning, perform fan start/stop tests to observe the valve flap opening angle, return speed, and closing tightness. For variable frequency fans, check the stability of the valve flap at low speeds.

Check valves installed on the outlet of indoor anti-corrosion fans, long-mounted in ceilings, pipe shafts, or workshops and connected to PPs flame-retardant ducts, become fire weak points in the entire flame-retardant pipeline system if made of ordinary combustible PP, potentially igniting first and spreading along the pipes during a fire. By adopting PPs flame-retardant check valves, the valve matches the flame-retardant grade of the duct and damper materials, self-extinguishing away from the fire, while retaining automatic anti-backflow functionality, meeting both fire protection and anti-corrosion requirements for indoor anti-corrosion exhaust engineering.

No. The function of PPs fire-resistant check valves is self-extinguishing of materials upon separation from the fire source and automatic prevention of air flow reversal. They do not possess fire protection features such as temperature-induced melting, electric closure, or fire resistance integrity. When air ducts pass through fire-rated compartments, floors, or server rooms, they must be installed in accordance with fire protection codes using certified fire-rated dampers or smoke exhaust dampers. The fire-resistant check valves are installed in indoor pipe sections either before or after the fire dampers, each serving its specific purpose. Fire-rated dampers must be installed where air ducts penetrate fire-rated compartments or floors. No plastic valves can substitute for fire dampers. After installation, fire inspection and acceptance must be conducted in accordance with regulations.

On-site simple inspection can be performed after the fan shutdown: observe if the valve disc seats fully, if the seal ring fits uniformly on the valve seat, and check for any air leakage sound or airflow sensation; under conditions, release tracer smoke on one side of the valve or use a manometer and anemometer to detect post-valve leakage. Quantitative acceptance can involve testing the air leakage rate of the valve section using air duct leakage detection methods and comparing it with the manufacturer's committed leakage level. During inspection, focus on checking for foreign matter, aging, or deformation in the seal ring, whether the valve shaft is horizontal, and if the petals of multi-leaf valves return synchronously.

Variable frequency fan low-speed operation may cause positive pressure difference near the valve disc opening critical point, leading to vibration and slapping of the valve disc, generating noise and affecting airflow. Solutions include selecting check valves with damping or adjustable weights to stabilize the valve disc after opening; optimizing fan control by setting a lower operating frequency limit to avoid the critical zone; for systems with significant operating condition variations and long-term low-speed operation, the check valve can be replaced with an electric sealed valve linked to the fan, which closes with a delay when the fan stops, ensuring smooth and controllable operation.

Must meet both corrosion resistance and flame retardancy. Seals are critical components for check valves to achieve sealing, directly contacting corrosive gases; if flame retardancy is prioritized over corrosion resistance, seals will swell, harden, and fail due to acids, alkalis, or solvents; conversely, if only corrosion resistance is considered without flame retardancy, they become combustible parts in the flame retardant system. When ordering, provide exhaust gas composition, concentration, and temperature, and the manufacturer will select an elastic seal material that meets both media compatibility and flame retardancy requirements, while material certificates should be obtained for spare part replacement using the same material specifications.

Required, although it requires no operation, the valve disc is a moving part. Regular inspection during fan maintenance should include: checking if the valve disc lifts and seats freely, if the shaft sleeve has crystallization or jamming, if the seal is aging or contaminated, if the limit stops are loose, and if the valve body welds are intact. Clean dust crystallization promptly, replace the seal when indentation is obvious or hardened and cracked, and inspect the shaft seat as required. For fans not operated for a long time, manually check the valve disc status before startup to prevent blockage and pressure buildup during fan operation.

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