trap primer - diagram

What Is A Trap Primer?

Why do you need to know what a trap primer is…or for that matter, what a trap is? Because homes, plumbing systems, electric systems, and even the ground can do weird things. Such as emitting a rotten odor you can’t ignore.

When that happens, it’s quite possibly due to sewer gas coming into your home from your floor drain. To keep that gas out, your drain requires a trap, and that trap needs a trap primer.

What Does A Plumbing Trap Look Like?

Let’s discuss the trap first. A plumbing trap looks like a U-shaped pipe. This U-shaped pipe also looks like the letter P on its side. That’s why plumbers call it a P Trap. It can be made out of metal or PVC (a synthetic plastic polymer which has a white-plastic look). Take a look under your kitchen sink or bathroom sink to see one for yourself.

What is a trap primer - u-shaped trap under toilet
As you can see, a P trap is simple. It’s just a U- or sideways P-shaped pipe that keeps water flowing out while keeping sewer gas from floating in. And yes, there are other shapes that accomplish the same thing.

How Does a Plumbing Trap Work?

All plumbing fixtures in a home have floor drains. The floor drains allow water to flow from your house and into a city’s sewer or storm drains. This keeps your floors dry and safe from water damage.

More so, each plumbing fixture — from kitchen sinks to toilets to showers to water heaters and more — is required to have a plumbing trap. The traps stop smelly sewer gases from coming up from the floor drain and into your home. However, in order for these plumbing traps to work — by “trapping out the sewer gas emissions” — water needs to drain into them to create a liquid seal. 

Put another way, here’s what’s happening. Water is trapped at the bottom of the U-shaped P Trap. This trapped water creates a seal in your pipe, which prevents any sewer gas from coming up through the drain and into your home. Sewer gas can’t get past the seal of water at the bottom of the U-shaped trap. It’s a simple but brilliant solution.

What is a trap primer diagram of of plumbing trap
In this diagram, you can see how water in the plumbing trap prevents sewer gases from getting through (back into the home) by creating a liquid or water seal.

What Is A Trap Primer And Why Do We Need It?

Just like the trap, a trap primer is relatively simple to understand. It’s a device that adds water to your plumbing trap. That’s it. And here’s why you need it.

If liquid doesn’t go down your drain often enough, the liquid seal – the water at the bottom of the U-shaped trap — will eventually evaporate. With the seal gone, sewer gas is now able to get through the drain pipe and into your home. That’s a serious problem, and can lead to a plumbing emergency (or even a health emergency; scroll down for more on that).

A trap primer (or trap primer valve) is a good idea for all of your plumbing fixtures. But don’t hesitate installing them on any plumbing fixtures that aren’t being used regularly. This could be an extra bathroom sink, shower and toilet; or perhaps in a vacation home you only visit once or twice a year.

Watch this video for a quick explanation of a trap and trap primer. The primer in this image is to the left. The trap is on the right.

Different Types of Trap Primers

  • Most simple method. Used most often with a floor drain trap is a quick connection from a sink that’s closely located. When the sink is used, some of the water goes to the trap.
  • Most common method. The primer connects to a drinkable water supply. When pressure per square inch (PSI) is sensed — such as from a nearby toilet or sink — it adds some of that water flow to the trap.
  • Other methods. Some trap primers work on timers (based on your settings for when a home is unoccupied). While others create plumbing devices (like a laundry faucet) has has a built-in trap primer. And there are other types as well.

Is Sewer Gas Harmful?

Sewer gas is not usually harmful in smaller doses. But sewer gas can be harmful over time, with prolonged, heavier doses, if the problem isn’t resolved. The primary gas in sewer gas is hydrogen sulfide. More so, studies have shown that large amounts are toxic to our oxygen systems, with the potential to damage organs and, in rarer circumstances, even cause death.

If you notice that there is an unpleasant odor coming from areas of your home where there are floor drains, you may want to check to make sure you don’t have a dry trap and do have a functioning trap primer.

Final Thoughts

In conclusion, trap primers are very important in your home. They prevent your p-traps from becoming dry so sewage gases have no way of leaking into your home. This can be especially helpful if you own a vacation home that you only visit around once or twice a year.

Call 1-Tom-Plumber

Our professional plumbers can help you identify or install a trap primer. We can even show you where you have floor drains and plumbing fixture traps througout your home.

Don’t hesitate to contact or call us at 1-Tom-Plumber (1-866-758-6237). We will immediately handle any emergency plumbingdrain cleaning and drain clearing, and water damage problem, including excavation of underground water lines and sewer main lines.

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