Flap Valve

Material: Body/Disc: Ductile Iron

Pin: Stainless steel 304

Hinge: Ductile iron, Body ring /Disc 

ring: Brass/Bronze

Coating: Internal and external with fusion bonded epoxy coating

Size: DN80-DN600mm

A flap valve is a one-way valve that automatically opens and closes based on the pressure of the medium or its weight. It is mainly used to prevent the backflow of the medium in pipelines or containers, while allowing the medium to flow smoothly in one direction.

I. Core Function: Why Do We Need a Shot?

Backflow protection

The core function of the flap valve is "unidirectional conduction and reverse cut-off": when the medium flows in the forward direction, the pressure pushes the gate panel to open, allowing the medium to pass through smoothly. When the medium attempts to flow in the reverse direction, the door panel automatically closes under the action of reverse pressure or its weight, tightly adhering to the valve seat to prevent the medium from flowing back and avoid equipment damage or system disorder.

For instance, in the effluent pipes of a sewage treatment plant, flap gates can prevent river water from flowing back into the treatment pool. A flap gate is installed at the outlet of the water pump to prevent the reverse impact of water flow on the impeller when the pump stops, thus protecting the motor of the water pump.

No external power required, energy-saving, and reliable

Unlike electric valves and pneumatic valves that require additional energy to drive, flap gates are fully opened and closed by relying on the pressure difference of the medium itself or the weight of the gate panel. They have no energy consumption and no complex control system. They are especially suitable for remote areas, outdoor or unattended scenarios, reducing operation and maintenance costs.

Reduce the water hammer effect

When the water pump starts or stops or the pressure in the pipeline fluctuates, the reverse impact of water flow may cause "water hammer", leading to pipeline vibration, rupture, or equipment damage. When the flap valve closes, it operates smoothly, which can buffer the impact force of reverse water flow, reduce the damage caused by water hammer, and protect the safety of the pipeline system.

Ii. Structural Features: How to Achieve Automatic opening and closing?

The structure of a flap gate is composed of core components such as the valve body, gate panel, hinge, and sealing parts. Its design details directly affect its performance.

Door panel design

Shape: Commonly circular, square, or rectangular, suitable for different pipe diameters and installation scenarios. For example, circular flap gates are mostly used for circular pipes, while square flap gates are suitable for square channels.

Sealing and hinge design

Sealing parts: The contact surface between the door panel and the valve seat is usually equipped with a rubber sealing ring. The elasticity of rubber compensates for tiny gaps to achieve a tight seal, effectively preventing leakage even under low pressure.

Hinge structure: The door panel is connected to the valve body through a hinge. The hinge shaft should be made of wear-resistant and anti-rust materials to ensure that the door panel opens and closes smoothly and avoid seal failure due to rust and jamming. Some flap gates are also designed with buffer devices to reduce the impact noise and wear during opening and closing.

Opening and closing control mode

Forward opening: It relies on the forward pressure of the medium to overcome the self-weight of the door panel and the friction force of the hinge. The greater the pressure, the larger the opening Angle. Generally, the maximum opening Angle is 60° to 90°, ensuring smooth medium flow and low flow resistance.

Reverse closing: When the forward pressure disappears or the reverse pressure is generated, the door panel rapidly closes under the combined action of the reverse pressure and its own weight, adhering to the valve seat to form a seal.

Iii. Applicable Scenarios: Which systems must be equipped with flap gates?

The application scope of flap gates is mainly concentrated in scenarios that require unidirectional flow and prevent backflow. Typical applications include:

Water supply, drainage, and sewage treatment

The effluent pipes of urban sewage treatment plants: To prevent river water from flowing back into the treatment system. 

Rainwater drainage outlets in residential areas or factories: To prevent water accumulation and backflow in municipal pipelines during heavy rain. 

Sewage pipes of septic tanks and sedimentation tanks: Prevent sewage from flowing back and causing pollution.

Pumps and pumping station systems

The outlet pipes of centrifugal pumps and submersible pumps: To prevent the reverse impact of water flow on the pump when it stops, and to protect the motor and impeller. 

Irrigation pumping station: Controls the unidirectional flow of water into the farmland channel to prevent irrigation water from flowing back to the water source.

Water conservancy and municipal engineering

Culvert, channel, and sluice outlet: Adapt to tidal and water level changes, and prevent the backflow of seawater and river water. 

Urban flood control and drainage pipelines: Allow rainwater to be discharged during the rainy season and prevent groundwater from flowing back during the dry season.

Industrial circulation system

The return water pipe of the cooling tower: To prevent the reverse flow of circulating water from affecting the system pressure. 

Chemical wastewater discharge pipeline: Prevent treated wastewater from mixing with untreated wastewater and flowing back.

The flap valve, with its characteristics of "passive opening and closing, maintenance-free and anti-backflow", has become a key device for ensuring the safety of unidirectional flow in fluid systems. Through reasonable selection and installation, it can work stably under various complex working conditions, effectively reducing the risk of system failure. It is a pipe accessory that is both practical and economical.