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Plumber Red Seal · Question

In a tall building, what is a primary purpose of installing relief vents or yoke vents in the suds pressure zones of a sanitary drainage stack?

Detergents can create suds that form a blockage in the drainage stack. This falling 'slug' can create significant positive air pressure below it, which can blow

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Question: In a tall building, what is a primary purpose of installing relief vents or yoke vents in the suds pressure zones of a sanitary drainage stack?

Answer options:

  • To introduce air and reduce the velocity of falling waste. ✅ To relieve positive pressure created by a slug of sudsy water.
  • To act as a secondary vent for fixtures in that zone.
  • To help siphon trap seals on lower floors to clear blockages.

Correct answer: To relieve positive pressure created by a slug of sudsy water.

Explanation: Detergents can create suds that form a blockage in the drainage stack. This falling 'slug' can create significant positive air pressure below it, which can blow out fixture traps. Relief vents are installed to dissipate this back pressure safely.

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