TRAPS

A trap is a section of piping that is required on every fixture outlet pipe that is meant to retain waste water in order to create a barrier between a buildings venting system and the open air of the building. These venting systems in the drain, waste and vent (DWV) piping systems of a building can contain sewer gases such as methane that can develop from human waste like poo poo. These gases can be flammable or hazardous and we do not these gases entering peoples homes or workplaces, this is why we use traps.

The different parts of traps include the wier which is the point on the outlet side of the trap where water is able to trickle down into the trap arm and into the rest of the drainage system. The trap seal depth is the actual part of the trap where water seals the travel of air into the open air of the house, with the minimum of that depth being 38 mm in usual applications. The dip is sort of like the opposite of the weir, it is the top part of the lowest bend of the trap. If water level goes below the dip, trap seal loss occurs. Trap seal loss means sewer gases in your home.

Pretty much all traps found in buildings are P-traps. These P-traps have a U shaped section of piping followed by a pipe that runs horizontal, slightly graded downwards but not enough that it runs under the dip of the P-trap. If it does run under the dip, it acts as an S-trap, a type of trap that is banned in Canada, becuase of the lack of ventilation it allows which could cause siphonage and trap seal loss.

DIME BLOC - The acronym for the usual ways trap seal loss happens in DWV systems (drain, waste and venting systems):

D irect siphonage...
occurs when a trap us poorly vented or has no vent to it. Every trap for every fixture requires a separate vent that connects to a stack, as the lack of pressure on the outlet side of a trap can lead to this type of siphonage, S-traps can contribute to siphonage and trap seal loss which is why they are prohibited.

I ndirect siphonage...
can happens whens when a fixture that has poor ventilation following its trap is further down along the plumbing system from another fixture. The pressure from the fixture that is upstream such as a water closet creates suction due to the poor ventilation of the lower fixtures trap so that when that suctioned water passes by the low pressure area of the trap arm, it sucks the water out of the trap and causes trap seal loss.

All these siphonage issues are caused by bad ventilation, imagine a full open bottle of water flipped upside down sluggishly pushing out of the bottom compared to if a hole was on the bottom of the bottle, the water would flow much quicker and more efficient (think of shotgunning a beer). This is why venting is so important alongside the sewer gases that form from our waste.

M omentum...
is caused by a fixture outlet pipe that is too long (longer than 1.2 meters). As the waste water leaves the fixture and travels down the fixture outlet pipe, momentum is build so when the water reaches the trap, it is travelling too fast and simply rushes through the trap, again causing trap seal loss. This can simply be prevented by designing the system so the fixture outlet pipe is shorter or installing offsets in that pipe

E vaporation...
is when water evaporates in the trap of a fixture, breaking the trap seal loss. Its that simple. This is most common when fixtures don't get used for a long time, like when people leave their vacationing cottages empty for the winter and all the dry air in these house suck the water out of the trap. There's also floor drains, which also need a trap seal to separate it from the venting system. The problem is though that people don't regularly pour water down floor drains to keep the trap seal, meaning that trap seal primers, a small water supply line that supplies a floor drain with small, controlled amounts of water to combat evaporation.

B ack pressure...
happens in the waste stack of taller buildings when large loads of waste allow for air pressure to quickly form at the base of these large stacks as it falls down with velocity. In buildings over 4 stories, when this air pressure forms at the base of these stacks, it can cause the waste to shoot back up the stack. If the drainage pipes of a fixture is connected too close to the base of a stack and this back pressure occurs, waste can shoot backwards in these pipes and even cause backflow into the fixture, causing it to overflow and create a big mess, along with trap seal loss. This can be prevented by limiting connections to these stacks at 1.5 meters above the base of the stack when there is a discharge of 30 fixture units or more (the measurement the a fixtures power potential relating to either its drainage or water supply).

L eakage...
is when the trap leaks, that's it. Replace da ting.

O scillation...
occurs when strong gusts of wind blow on the vent terminal of a building, and that wind is able to rock the water in a trap and cause it to slowly spill over the wier, causing trap seal loss. There isn't really a way to fix oscillation unless you can somehow limit the weather or build some convoluted contraption that stops winds from finding its way in the vent terminal but other than that, nada.

C apillary action...
can happen when you have a piece of foreign debris like a strand of hair or a string from a mop that is positioned to lay over the weir so that one end is in the trap seal and the other end is in the trap arm, positioned on a nominally horizontal slope. Capillary action feeds the water from the trap into the matter and drips it into the trap arm, creating trap seal loss. This can be fixed by cleaning the trap which is made easier by adding a cleanout.