What is the maximum height of the liquid seal in fixture traps, except for specially-designed fixtures?

The maximum height of the liquid seal in fixture traps is typically established to ensure effective odors and gas sealing while allowing proper drainage. A height of 4 inches provides a sufficient liquid barrier to prevent sewer gases from escaping into the living space while also accommodating the necessary flow of wastewater. This specification is critical for ensuring the trap functions correctly under various conditions that may affect wastewater movement.

Other potential heights such as 2, 3, or 5 inches do not provide the right balance between effective sealing and functionality. Too low of a liquid seal may not prevent gas escape effectively, and too high of a seal could lead to drainage issues or trap siphoning during heavy flow situations. Therefore, setting the maximum height at 4 inches helps maintain the integrity of the plumbing system under standard operating conditions.