Have you ever come home to the smell of sewage? Have you ever lost a valuable down the drain? Have you ever had a sewer back up in your garage or basement? Some of us have experienced these issues in the past and knowing what a trap is and how it functions is integral to solving these common household problems.
So what is it?
A trap is a U shaped pipe located under sinks, tubs, shower, washing machines, and pretty much anything that connects to your sewer line system. They can be seen quite easily, just open up the cabinet under the sink in the kitchen or look at the side of the toilet. There are many different types of traps, the most common being P-traps (pictured below). Others include drum traps, S-traps, ¾ S traps, running traps, and building traps. It is important to know that not all traps are allowed by code and different traps are used for different facilities or drain systems.
Installation is Everything
Traps, in all their various shapes and forms, are designed to stop sewer gas permeating through the plumbing in a house. They are also good for catching valuables lost down the drain. Sewer gas itself is some really nasty stuff. Methane, Hydrogen Sulfide, Carbon Monoxide are all common gases produced by sewage and waste. These gases, in high enough concentrations, could be detrimental to your health. Whenever water is used in a facility, centrifugal force is created. The velocity of the water breaks the seal and forces the wastewater down the sewer line and out towards the main. After a toilet is flushed or the sink is turned off, a small amount of water is left in the bottom of the trap. This small amount of water acts as a seal to prevent any sewer gases from coming back up the line. Installation of a level trap is critical to keeping the seal. Improper installation can result in back siphonage and ultimately, those gross sewer smells.
The depth and width of a trap is also critical to its function. For instance, if a trap is too deep, the increased force of the water flowing through the trap could potentially cause a siphon. Water that would typically remain in the bottom of the trap creating the seal, could be sucked out with the initial flush. In order to fall within code, traps typically have to be self-cleaning and must be able to flush away debris such as hair and lint. A p-trap that does not self-clean properly is liable to capillary action. This is when a piece of hair or lint hangs over the outlet of the trap. The water will climb up the string using capillary action and drip out. This will eventually cause the trap to lose its seal. Traps are also not allowed to depend on moving parts to create a seal. For proper self-cleaning and siphoning, the outlet of the trap must be the same size as the fixture drain.
The Problem with Cast Iron Traps
The age of your house will typically determine the material the trap is made from and potentially the condition of the pipe. Our team at Mister Sewer comes across a lot of cast iron traps in basement and garage drains. Cast iron is a durable material but it is susceptible to corrosion (as seen on the left). Corrosion can cause scaling inside the trap and can create its own sewer blockage problems. A build-up of corrosion in a trap can potentially prevent a plumber from being able to hydro jet or snake a sewer line effectively due to access from the trap to the rest of the line. Modern traps are made of plastic, particularly PVC or ABS. The smooth surface is not liable to corrosion or scaling. A PVC trap will provide just as much durability and a longer lifespan than the conventional cast-iron trap.
For such a simple design, traps are actually quite complicated. In order to work efficiently and effectively, the trap must meet code designs and must be installed properly in accordance with the rest of the plumbing system. Next time you smell sewage, consider the last time you have had your sewer system inspected by a professional. It could very well be a trap in your home or basement. If you have more questions or would like us to assess the condition of your house trap, we encourage you to reach out to the sewer experts at 412-835-2135 or click here to schedule an appointment.