PP Check Valve

Product Model	PP soft seal check valve
Category	PP Machined Products
Reference Price	Price on request

Hot Customizable for Working Conditions 11 Technical Parameters

Product Overview

The PP check valve, also known as a one-way valve or non-return valve, is a plastic valve that allows airflow to pass in only one direction while automatically preventing reverse flow. It is installed on the outlet of corrosion-resistant fans or pipelines requiring prevention of gas backflow. It does not have an actuator or operating handle. Forward airflow lifts the valve disc, and upon fan shutdown, reverse airflow and the valve disc's self-weight cause it to automatically reseal, with the soft seal ring pressing against the valve seat to achieve low-leakage closure.

When the fan shuts down, if the pipeline is connected to an outdoor exhaust stack, parallel fans, or other areas, natural wind pressure, thermal pressure, and other operating fans may cause reverse airflow, leading to cold air infiltration from outdoors, corrosive gas intrusion into idle equipment or adjacent workshops, or harmful gas dispersion. The check valve automatically closes in an instant without power, control signals, or manual operation, making it the most economical and reliable device for preventing backflow. The soft-seal structure results in significantly lower leakage compared to conventional flap valves.

The PP check valves supplied by Xicheng Environmental Protection are available in molded or plate-welded body designs, with single- or multi-lobed hinged valve discs, equipped with soft seal rings and limit structures. The valve shaft is horizontally installed to allow the valve disc to close under its own weight. Available in circular, square, and various sizes, they can be selected with flame-retardant requirements for flame-retardant PP check valves.

Working Principle

The check valve operates automatically based on airflow pressure differential and the valve disc's self-weight, making it a self-actuated valve. When the fan is running, forward airflow creates a pressure differential on both sides of the valve disc. When the thrust generated by this differential exceeds the valve disc's self-weight and the friction of the shaft, the valve disc pivots around the shaft, opening the valve for airflow. The greater the airflow, the larger the valve disc opening, which is limited by a stop structure. After the fan shuts down, the forward pressure differential disappears, and the valve disc falls under its self-weight. If reverse airflow exists, the reverse pressure further presses the valve disc against the valve seat, quickly closing the valve.

The sealing function is achieved by the soft seal ring on the edge of the valve disc. When the valve disc reseats, the seal ring presses against the valve seat, and the tighter the reverse airflow pressure, the more reliable the seal—this is the unique self-sealing characteristic of check valves. The PP valve body and valve disc are resistant to acid and alkali corrosion, do not rust or jam, and the shaft is made of corrosion-resistant material with a lightweight bearing, ensuring long-term flexible operation and proper reseating. The valve disc is designed as a lightweight structure, requiring only a small forward airflow to open and reducing resistance during normal operation.

Structural Components

The check valve consists of a valve body, valve disc, shaft, seat seal ring, limit device, and end connections. The valve body is a molded cylindrical or plate-welded cylindrical shell with a valve disc pivot space inside. The valve disc is a circular plate or a multi-lobed assembly with a corrosion-resistant soft seal ring embedded at the edge. The upper part is hinged to the valve body via the shaft, allowing it to pivot in one direction, and the shaft must be horizontally installed to ensure self-weight closure.

A flat valve seat is set in the fully closed position of the valve body, and a limit block or limit rod is installed on the opening side of the valve disc to restrict maximum opening and prevent excessive rotation. The shaft is made of stainless steel-coated or corrosion-resistant material, with a lightweight shaft sleeve for smooth rotation. Large-diameter check valves use a multi-lobed structure to reduce the size of a single lobe and the opening pressure differential. The valve body is connected at both ends via spigot or flange, with slight differences between vertical and horizontal installation structures. Orders and installation must follow the valve body orientation markings.

Specification Model Table

The following table compares the functional differences between check valves and other types of fan valves, with selection determined by function.

Valve Type	Operation Mode	Function
Check Valve	Self-actuated	Prevent reverse flow
Regulating Valve	Manual / Electric	Control airflow volume
Isolation Valve	Manual / Electric Pressure	Actively isolate pipeline

Product Features

The PP check valve automatically prevents backflow, features soft sealing with low leakage, and requires no power, making it an economical device for fan shutdown protection. Key features include:

Automatic opening in the forward direction and closing in reverse, requiring no operation
Independent of power and control signals, providing automatic protection upon shutdown
Soft seal ring with reverse self-tightening for minimal leakage
PP material resistant to acid and alkali corrosion, with non-rusting and non-jamming valve discs
Lightweight valve disc requires low opening pressure differential, reducing operational resistance
Effectively prevents air infiltration, cross-contamination, and harmful gas dispersion
Available in single- and multi-lobed structures, with customizable sizes

Body Material	PP Polypropylene
Sealing Form	Soft Seal Ring Self-Tightening
Action Method	Self-Acting Angle Valve
Drive Energy	No power required
Valve Disc Type	Single-petal / Multi-petal
Installation Requirements	Shaft Axis Horizontal
Corrosion resistance performance	Acid and Alkali Salt Resistance
Connection Method	`Spigot / Flange`
Function	Prevent air flow backflow
Flame Retardant Options	PPs self-extinguishing
Resistance Characteristics	Low resistance in fully open state

Application Industries

Preventing gas backflow into the system from the fan outlet during anti-corrosion operations
Preventing cross-flow between multiple parallel fans
Preventing outdoor air from infiltrating into the exhaust stack at the bottom
Automatic isolation of bypass circuits for single-use and backup purification equipment
Preventing cross-contamination in laboratory ventilation shafts
Preventing gas leakage between workshop exhaust and adjacent areas
Preventing cold air from infiltrating pipelines after fan shutdown during winter

Typical Process Locations

The most typical installation location for check valves is the fan outlet pipe section. When the fan is running, the valve disc is blown open, and it automatically closes after shutdown to prevent backflow from the exhaust stack and natural wind. When multiple fans are connected to a single main pipe, a check valve is installed at each fan outlet to prevent the airflow from operating fans from backflowing into standby fans. Backup equipment bypass circuits are also automatically isolated by check valves. The installation location should be near the fan outlet, and sufficient space must be left around the valve for the disc to swing.

During installation, it must be ensured that the valve shaft is horizontal, the disc's weight is oriented toward the closing direction, and the valve body's airflow direction indicator aligns with the actual airflow. Incorrect installation may result in the disc being unable to open or close properly. Pipe supports must be installed before and after the valve, and no debris or other components should be within the disc's operational range. When starting the fan, observe whether the disc opens normally and whether there are any abnormal noises. When shutting down, observe whether the disc returns to its seated position quickly. Check valves cannot replace isolation valves requiring active shutdown; when manual or electric isolation is required, a sealed valve must still be used.

Soft-sealed check valves exhibit minimal air leakage when the valve disc seats properly, the seal ring is intact, and there is reverse pressure; they can meet general anti-backflow and anti-cross-contamination requirements. However, as self-actuated ventilation valves, their sealing force derives from the valve disc's weight and reverse pressure differential, with limited sealing force when the reverse differential is small, making them not equivalent to actively tightened closed valves or industrial pipeline check valves. In scenarios involving strict isolation of hazardous gases, explosion-proofing, and personnel safety, electric or manual closed valves should be installed in series, not relying solely on check valves.

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.

Strict directional requirements apply. The arrow or directional indicator on the valve body must align with the forward airflow direction, and the valve shaft must be installed horizontally to allow the valve disc to smoothly settle onto the seat under its own weight. Check valves for horizontal and vertical pipelines have different structures and cannot be interchanged: horizontal pipes require swing check valves, vertical upward pipes require vertical check valves, while vertical downward and horizontal downward airflow scenarios require the corresponding types. Incorrect installation can prevent the valve disc from opening properly, causing air restriction and fan overload, or result in failure to close and loss of check function. After installation, manually operate the valve disc to verify correct swing direction, smooth reseatment, absence of sticking or abnormal wear. The valve shaft levelness and the clearance between the valve disc and seat must also be checked. Any directional or levelness issues must be adjusted before operation.

Failure to open is often due to incorrect installation direction, valve shaft jamming, valve disc being stuck by foreign objects, or crystallization at the shaft seat; failure to close tightly is often due to foreign matter between the valve disc and seat, damaged seal ring, valve shaft not in horizontal position, valve disc deformation, or rusted rotating shaft; during troubleshooting, shut down and open the maintenance port, clean the jamming objects and crystallization, check the valve shaft horizontal degree and rotation flexibility, replace aging seal ring and damaged shaft sleeve. Corrosion-resistant check valves should regularly inspect the valve disc status during fan maintenance, clean the dust and crystallization before putting back into service.

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.

Not applicable. Check valves automatically prevent reverse flow and remain open during forward flow, cannot actively shut off forward airflow, nor remote control; electric sealed valves can actively close per command for bidirectional isolation but require power and control signals, with status depending on reset mode during shutdown/power loss. Check valves are simple and reliable for preventing backflow at fan outlets, while electric or manual sealed valves are used for maintenance isolation and hazardous gas cutting; both are used in series for high-demand applications, each performing automatic check and active isolation functions.

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