Definition and function

A vent cap is a small device that is installed on top of a drainage system or container. Its main function is to balance the air pressure inside and outside the system, so that the gas in the drainage pipe or container can be smoothly discharged, while preventing foreign objects (such as dust, insects, rain, etc.) from entering the system. For example, a ventilation cap is installed on the top of the drainage riser of the building. When the sewage flows in the pipeline, the air in the pipeline can be discharged to the atmosphere through the ventilation cap to avoid poor drainage due to pressure differences.

Structure and working principle

Structure composition: The ventilation cap is generally composed of a cap body, a vent hole and a protective device.

The cap body is usually a small cover, with various shapes, common round, square and so on. Its material is plastic, metal and so on. Plastic ventilation cap light weight, corrosion resistance, relatively low price; Metal ventilation caps (such as stainless steel ventilation caps) have high strength and good durability, and are suitable for use in some occasions with high strength requirements or harsh environments.

The air vent is distributed on the cap body, and its size, number and shape are determined according to the design purpose and flow requirements of the ventilation cap. The role of the air vent is to let the gas through to ensure that the air in the pipeline is connected to the outside atmosphere.

The guard is used to prevent foreign objects from entering. Some ventilation caps have a screen or shutter structure at the vent. Filters block small particles such as dust and insects, while shutters prevent large amounts of liquid such as rain from pouring directly into the pipe while allowing gas to pass through.

Working principle: When the pressure in the drainage pipe or container is higher than the external atmospheric pressure, the gas is discharged into the atmosphere through the vent hole of the ventilation cap; When the air pressure in the pipeline is lower than the outside atmospheric pressure, the outside air can enter the pipeline through the vent, thus balancing the air pressure. For example, in the drainage system of the toilet, when the water is flushed, the air in the drainage pipe is squeezed by the sewage and discharged through the ventilation cap; When the drainage is completed, the air pressure in the pipeline is reduced, and the outside air will enter the pipeline through the ventilation cap.