What height needs to be achieved in a barometric loop to effectively prevent back siphonage?

To effectively prevent back siphonage in a plumbing system, a barometric loop must be constructed to a sufficient height that creates enough hydraulic pressure. The correct height to achieve this is 35 feet. This height is significant because it corresponds to the atmospheric pressure that can counteract the vacuum conditions that lead to siphoning.

When water is drawn from a plumbing system, if there is a sudden drop in pressure, it can create a siphoning effect that pulls potentially contaminated water back into the clean water supply. A barometric loop, when designed to a height of 35 feet, generates the necessary atmospheric pressure to prevent this backflow scenario. This is based on the principle that water can only be lifted by atmospheric pressure, which is about 14.7 psi at sea level, equivalent to the ability to lift water approximately 34 feet.

While other options such as 30 feet, 40 feet, or 25 feet may appear plausible, they do not ensure sufficient protection against back siphonage. Specifically, heights lower than 35 feet may not provide adequate back pressure for effective prevention, while excessively high structures like 40 feet do not have practical applications in typical plumbing design and could lead to inefficiencies or added complexity in the system.