Trap primer
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A trap primer (or trap seal primer) is a plumbing device or valve that adds water to traps. The water seals in traps are needed to prevent sewer gases from entering buildings, but because this water is exposed to the air, it is subject to evaporation over time in infrequently used floor drains, leading to the release of sewer gas into the environment. The trap primer mitigates this problem by injecting water, either directly or indirectly, into the trap to maintain the water seal indefinitely.
Building codes may require trap primers for some traps, especially for where experience has shown that there are isolated and/or infrequently used drains such as basement floor drains (which are only used when the basement is flooded). Where explosion hazards are high, specifying trap primers, whether required or not by code, is wise. Trap primers do require maintenance and replacement, so they should be installed in accessible locations.
Types
There are many types of trap primers. The simplest, typically for a floor drain's trap, is simply a connection from a nearby sink's drain so that when the sink is used, some of the water flow is diverted into one or more traps. More common is a primer that is connected to the potable water supply and activates when pressure fluctuations are sensed, such as the flushing of a nearby water closet. Others depend on occupancy sensors or timers. Several manufacturers (e.g., Moen) produce laundry faucets with a built-in trap seal primer outlet.
Other solutions
In infrequently used floor drains where such a primer does not exist, evaporation can be mitigated a few different ways:
- Routinely adding water to the floor drain
- Pouring a small amount of vegetable or mineral oil into the drain to just cover the trap's water surface. The oil floats on the surface of the water and creates a liquid seal preventing further evaporation. Mineral oil tends to be a better option, as it does not go rancid, where vegetable oil does. Any environmental impact from its discharge is negligible compared to the contents that can be flushed out of a flooded basement.
- Where acceptable by local code, inline trap sealer (i.e. Canplas SureSeal) can be installed.
Poor venting or windy conditions can cause water seals to be siphoned or blown out; for these cases, the drain must be refilled.
See also
