What Is a Trap Primer?
A Trap Primer is a plumbing device that adds water to a drain trap when the trap may dry out. The added water helps maintain the trap seal, which blocks sewer gases from entering a building. Trap primers commonly serve floor drains in areas that receive little regular water flow.
Quick Facts About Trap Primer
Category
Drain trap protection device
Used for
Infrequently used floor drains
Common confusion
Not a drain trap or drain cleaning chemical
Also called
Trap seal primer, Automatic trap primer
Often discussed with
Drain Cleaning
Key Takeaways About Trap Primer
- It serves traps that may lose water through evaporation.
- A primer connects to a water supply or nearby fixture line.
- It isn't the same as a drain trap or drain cleaner.
How Trap Primer Works
Trap Primer sends a small amount of water into a drain trap when water use creates a pressure change in the supply line. Some models connect to a nearby fixture line, while others use a dedicated water connection. The primer directs water through a tube that ends above or inside the trap.
Related glossary terms: Drain Trap, P-Trap, Cleanout.
The water restores the trap seal after evaporation lowers it. A working seal blocks sewer gases from moving through the drain opening. During drain cleaning, the trap primer and its tubing may be checked if a floor drain smells, dries out, or drains poorly.
Where It Is Used
- Floor drains in utility rooms.
- Drains in mechanical spaces.
- Low-use areas that rarely receive poured water.
Expert Note
When we work on drain cleaning, we check whether a floor drain has a working trap seal. We inspect the primer connection, its tubing, and the drain opening for blockage. A blocked primer line can leave the trap dry even when the device appears installed.
Trap Primer in Practice: A Real-World Example
A utility-room floor drain rarely receives water, so its trap may dry out and allow sewer odors. A trap primer connected to a nearby supply line adds water when that line operates.
Related Services
Related Terms
Drain Trap
A Drain Trap is a curved section of drain pipe that holds a small amount of…
P-Trap
A P-Trap is a curved drain fitting that holds a small amount of water beneath a…
Cleanout
A cleanout is an access point in a drain or sewer pipe. A removable cap covers…
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