What causes trap siphonage and back siphonage pressure in a drainage system?

Trap siphonage and back siphonage pressure in a drainage system are primarily caused by pressure differences between the drainage system and the atmosphere. When water flows through the pipes, it can create negative pressure or a partial vacuum in certain areas, particularly near traps. This negative pressure can siphon water out of traps, which are designed to hold a water seal to prevent sewer gases from entering the living space.

Back siphonage occurs when the atmospheric pressure surrounding the drainage system is lower than the pressure within the system itself. This can happen in scenarios like a sudden drop in water pressure due to a break in the supply line or high demand elsewhere in the system. In such cases, the atmospheric pressure can draw water from traps, potentially leading to the loss of the water seal.

Understanding the significance of maintaining pressure balance in a drainage system is crucial for preventing the occurrence of siphonage and back siphonage. Proper venting in plumbing systems is essential to ensure that pressure differentials are minimized, effectively maintaining the integrity of the traps.