What does venting protect the trap seals from, besides positive pressures?

Venting plays a crucial role in maintaining the functionality of plumbing systems, particularly in protecting trap seals. Trap seals are essential because they prevent sewer gases from entering the building while allowing wastewater to flow through the drainage system. One of the significant threats to trap seals is siphonage, which occurs when negative pressure is created in the drainage system, potentially causing water to be drawn out of the trap.

When water flows through the drainage pipes, particularly if there is a sudden change in flow or if multiple fixtures are draining at the same time, the changes in pressure can lead to siphonage. The venting system alleviates this risk by providing air into the system, balancing the pressure and ensuring that the trap's seal remains intact. This balance prevents the displacement of water from the traps, preserving their integrity and thus preventing the escape of harmful odors and gases into the living space.

By ensuring that sufficient air can enter the drainage pipes through the venting system, siphonage is effectively mitigated, thus safeguarding the trap seals. This is a fundamental aspect of plumbing design and installation, contributing to the overall health and safety of the plumbing system.