The primary function of a vented loop in a plumbing system is to:

The primary function of a vented loop in a plumbing system is to prevent siphoning. Siphoning can occur when there is a change in pressure that allows fluid to be drawn back from a discharge point, such as a sink or toilet, back into the supply lines. A vented loop creates an air gap that helps maintain atmospheric pressure within the system, effectively breaking the siphon and preventing any unwanted backflow of contaminated water or waste back into the clean water supply. This essential function protects the integrity of the potable water system and ensures the safe operation of the plumbing.

Understanding this helps clarify the importance of venting in plumbing systems. Rather than focusing on maintaining pressure or drainage, the vented loop specifically addresses the potential for siphoning, thereby safeguarding public health and maintaining system functionality.