Visszafolyó

Visszafolyó is a Hungarian term used to describe the undesired reverse movement of liquids or gases in a closed system, such as pipes, channels, or containers. It occurs when the pressure on the discharge side falls below the pressure on the supply side, or when a flow path becomes exposed to a higher-pressure source while the downstream path remains open. The concept is applied across engineering disciplines, including plumbing, water supply, sewerage, irrigation, and industrial processes.

In buildings and infrastructure, backflow can allow contaminated water from sewer lines or process streams to re-enter clean supply lines, creating health and safety risks. In natural systems, backflow can occur in rivers during floods or in groundwater when hydraulic gradients reverse. Causes include backpressure, back-siphonage, cross-connections, blockages, and equipment failures. Effects range from nuisance wet areas to serious contamination of drinking water or process streams.

Prevention and control rely on backflow prevention devices and proper system design. Common protections include check valves (one-way valves), backwater valves, air gaps, and vacuum breakers. Regular testing, maintenance, and adherence to relevant standards or building codes are essential, particularly in facilities handling potable water or hazardous materials. In Hungary and many jurisdictions, risk assessments and mandatory installation of backflow protection may be required for certain applications.

Etymology: the word is a compound of vissza (back) and folyó (flow). In Hungarian technical language, visszafolyó is used to refer to the general phenomenon of backflow, with visszafolyás as a closely related noun form.