What is the purpose of a trap in a sanitary drainage system, and what are the requirements for trap seals?

A trap in a sanitary drainage system is a U-shaped or S-shaped fitting designed to hold a certain amount of water, creating a seal that prevents sewer gases from entering the building. Sewer gases contain potentially harmful and unpleasant odors, and some components, like methane, can be explosive. The water held within the trap blocks the passage of these gases, effectively sealing the drain opening. The primary purpose of a trap is to maintain this barrier against sewer gases. The requirements for trap seals are specified in plumbing codes to ensure the trap functions correctly. A trap seal must maintain a minimum depth of water, typically 2 inches, to provide an effective barrier against sewer gases. The maximum depth of the trap seal is also regulated, typically limited to 4 inches, to prevent excessive backpressure and siphoning. The trap must be self-scouring, meaning that it is designed to be cleaned by the flow of wastewater, preventing the accumulation of solids and debris. The trap must be properly vented to prevent siphoning, which can occur when the pressure in the drainage system fluctuates, drawing the water out of the trap seal. The trap must be accessible for cleaning and maintenance. Cleanouts are often installed near traps to allow for easy access. The trap must be made of durable and corrosion-resistant materials, such as PVC or cast iron, to ensure its long-term performance. Proper trap design, installation, and maintenance are essential for preventing sewer gases from entering the building and maintaining a safe and sanitary environment.