Toilet roof vent

The first skill that a new homeowner should acquire is toilet repair. 1 had my first lesson on this vital skill in 1969. We had just moved into our first house in south Chicago when 1 discovered our toilet wouldn t flush. An experienced co-worker at the American Oil Refinery in Whiting, Indiana (now BP), suggested that 1 check the roof vent (see Fig. 1.2). 

This suggests that the pressure in a water drain can get so low, that air could be sucked out of the bathroom and down the drain. Of course, we all see this happen several times a day—typically when we flush a toilet. So much air is drawn into the water drainage piping, that we install vents on our roofs, to release this air. The only requirement, then, for vapors to be drawn into a flowing nozzle is for the nozzle exit loss to be larger than the static head of liquid above the nozzle. 

Incidentally, if a bird builds its nest on top of one our roof toilet vents, we find the toilet will no longer flush properly. The experienced plumber states that the toilet won t flush because it is suffering from vapor lock and this is true. A working knowledge of process equipment fundamentals often comes in quite handy around the home. 

Climbing onto the roof I found that a pigeon had built its nest on top of the 3-inch diameter vent pipe. I removed the nest and the toilet flushed just fine. The water swirled around merrily in the bowl for a few seconds. Next, the water gushed and rushed down the toilet s drain with wonderful speed and vitality. The water seemed to be in such a hurry to leave the toilet bowl and escape through the sewer that it dragged a small amount of air with it. 

When the air-water mixture enters the larger, vertical stand-pipe in Fig. 1.2, the velocity of the air-water mixture goes down. Some of this reduced kinetic energy is converted back into pressure. This I know because the pressure in the stand-pipe is atmospheric pressure. This has to be because the top of the stand-pipe is the 3-inch vent pipe sitting on the roof of my house. The air sucked down the toilet bowl escapes through this 3-inch vent. If a bird s nest or snow clogs the vent, then the trapped air builds pressure in the stand-pipe. The backpressure from the stand-pipe restricts the flow of water from the bowl, and the toilet can no longer flush properly. 

Incidentally, if a bird builds its nest on top of one of our roof toilet vents, we find the toilet will no longer flush properly. The experienced... 

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