Sylvan – fresh air inlet?

[MasterPlumbersKeymaster]

To fix negative pressure —

What is a fresh air inlet?

What is a double vent running trap on the house main?

Someone suggested putting a windbreak type contraption on the rooftop vents. Will this do anything to stop the loss of water in traps on windy days and/or improve slow drains?

[SylvanLMPParticipant]

To fix negative pressure —

What is a fresh air inlet?

Answer. F. A. I is located with in 4 feet of the building house trap (Upstream) and it is half the diameter of the building house drain (trap) BUT in no case less then 3″ diameter and shall be located 6″ above grade minimum (very important) and exposed to the outside air for the purpose of drawing fresh air in.

What is a double vent running trap on the house main?

Answer. A double vent trap is a running trap with two openings on top that are normally used as clean outs. One up stream and one for the street side of the trap.

SNIP >Someone suggested putting a windbreak type contraption on the rooftop vents. Will this do anything to stop the loss of water in traps on windy days and/or improve slow drains?<SNIP

Answer> OK lets talk plumbing as you seem like a very intelligent person asking the right questions (For once a live on this list thank you lord )

As you may know a vent is used to remove objectionable gases and improve drainage flow by equalizing atmospheric pressure.

For example take a 2 liter Pepsi bottle and fill it with water and then hold it up side down plop, plop, plop as the liquid inside this bottle is causing a slight vacuum and is starving for air it is very sluggish at draining.

Now take this same bottle and put a hole in the opposite side and WHOOSH you have a faster draining funnel JUST like a properly vented plumbing system.

Now if you should slightly close this hole (restricting the vent opening) you again are causing a drainage problem SO I guess the “wind break” idea is not so good huh?

What you can do to prevent a down draft situation is a big city trick we use when the adjacent sky scrappers play havoc on venting is we use what is commonly called a “return bend” which is nothing more then a 180 degree fitting or arrangement of fittings to offset drafts.

This still gives full flow in volume BUT wont allow any down drafts Or in NYC’s case vandalism of 2 legged animals throwing bottles or cans down an open vent pipe.

Now lets move on to 1st year apprentice stuff.

The fresh air inlet called in the trade the F. A. I.. Being at ground level (6″ above grade) this being the heavier air and this inlet draws cold fresh heavy air into the drainage system.

As this fresh air gets warmer from the heat of the building AND picking up lighter sewer gases like methane and other great stuff like hydrogen sulfide it looks to rise as it is lighter then the cooler fresh air.

Thus it looks for an opening and here we find a vent line waiting for this rancid smelling gas to enter it.

Now the updraft on high rise buildings is AMAZING 60 Stories or more sucking everything up if we didn’t allow for it with various plumbing tricks, but on lower buildings nature is our friend and Nature helps equalize the pressure with a vent and helps remove foul odors.

UNLESS some engineer comes along looking to add CHEAP UNPROFESSIONAL AAV’s plastic garbage that rely on a piece of junk rubber for integrity.

Thank you so much and if you have any questions please feel free to send me an E mail any time. Have a great week end.

All kidding aside there are some really nasty gasses present in sewers which can be a real health hazard

[Author]

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