What Does SLAMOBEC Mean in Plumbing?


SLAMOBEC stands for siphonage, leak, aspiration, momentum, oscillation, back pressure, evaporation, and capillary attraction, and refers to the different ways a plumbing trap can lose its seal.

Breaking down each component of SLAMOBEC

  • Siphonage – is caused in two main ways. The first way is through negative pressure. If there is less pressure in the plumbing system than in the drainage pipes, it will pull water out of the trap seal. Negative pressure can also be caused by back pressure, which occurs when the incoming water is flowing too quickly. If this happens it can force air into the trap seal. The other way siphonage can occur is through something called self-siphonage. Self-siphonage can be caused by an inverted trap or a momentum pull.
  • Leakage – is caused by a gap or crack in the pipe that allows water to seep out of the trap.
  • Aspiration – if an unvented siphon trap is used, the water discharge from one fixture in a building can cause a vacuum in the branch waste pipe of a lower level fixture. This causes water to be forced out of the trap and into the stack.
  • Momentum – is when water exits too quickly, causing the trap to lose its seal.
  • Oscillation – can occur when wind from inclement weather affects the pressure inside the piping, which can cause the trap to lose its seal.
  • Back pressure – is when the air pressure in the drainage system increases. When water flows down a stack (the drain from upper floors in a building), it pulls air along with it. This air volume will flow through the building’s drain and into the sewer drainage system, unless there is a blockage that stops the air from getting through. If there is a blockage, like when the building drain is full, or when there is a building trap or backwater valve, then the increased pressure can have an adverse effect on trap seals.
  • Evaporation – is when water evaporates from the trap and leaves behind air, which can cause it to lose its seal. Commonly occurs in locations with warm dry weather.
  • Capillary attraction – wicking away of water by hair, cloth or other fibers that are lodged in an S-trap

How to prevent trap seal loss?

These conditions causing a plumbing device to lose its seal can be prevented through the use of effective drains, vents, and traps. Frequent cleaning helps maintain traps and prevent debris from clogging drain lines. Traps should be inspected routinely by a professional plumber to ensure they are in proper working order. In addition, it’s usually best to replace old pipes, fittings, and traps with newer ones. This helps prevent the problem from occurring altogether.

What to do when your plumbing trap loses its seal?

If you suspect your plumbing trap has lost its seal, call a licensed plumber immediately. Do not attempt to fix the issue yourself. A properly functioning trap is critical for your home’s plumbing and health.

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