Check Vents

[Pete Masterson]

The whole point of the vent system in waste lines is that the moving
water creates high/low air pressure in front and behind the 'blob' of
water. Venting allows the air pressure to equalize, allowing the
water to flow quickly and without 'glugging' as it moves down the pipes.

Because of the way the pipes have to run in an RV (any RV, not just a
BB), there are often under-sink vent valves as a (second or third)
through-the-roof vent may be impractical. If properly installed, and
not stuck open, the under-sink vents should not be allowing sewer gas
from the tank(s) to enter the coach.

The primary vent (to the tank) is designed to allow sewer gasses to
escape and prevent a build up of pressure as well as to allow air to
be displaced as water runs through the pipes... but there may be
turns and drops in the run that isolate sections of pipe when they're
filled with water, hence the need for an additional vent to relive
the pressure differences.

If you look at a piping diagram for a typical home, you'll see that
there are multiple vent lines that often join together to minimize
the number of through-the-roof vents -- but usually there are vents
serving each 'set' of drain lines. For example, my home has a vent
stack near the kitchen, another near the washing machine and laundry
tub, and a third near the bathrooms (that are 'siamese-style' to
share plumbing). This multiplicity of vents often isn't practical in
an RV.

Pete Masterson
'95 Blue Bird Wanderlodge WBDA 42
aeonix1@...
On the road at Lockhart Texas



On May 27, 2007, at 9:16 AM, jwasnewski wrote:

> There is a check valve vent, normally closed, on the sewer system
> under
> each of my sinks. What is there purpose? The only thing I can come up
> with is to relieve gas pressure and stink up the coach in the event of
> an external roof vent becomes clogged??????Any ideas.