Plumbing traps have a long history dating back to 1775 when the S-trap was invented. However, following the 1948 ban on S-traps in most states, more trap designs came into the limelight.
So, what types of plumbing traps do we have? There are 15 types of traps in a drainage system, including both permissible and prohibited types. The S-trap, P-trap, Q-trap, Gulley trap, and floor trap are the most common. Other popular entrants are the intercepting trap, bottle trap, and grease trap.
We’ll examine each plumbing trap, touching on the purpose, area of application, and its limitation. Also, we’ll look at maintenance tips and plumbing traps you might want to avoid.
Plumbing Traps and How It Works
Let’s first start with the basics. Primarily, what is a plumbing trap? Also, how does it work?
Think of a trap as a curved or bent pipe section, mostly with a U, J, or S-shaped design. This bent or curve retains a small amount of water, creating a water seal barrier between the sewer line and living space.
The purpose of the trap is to prevent sewer gases and foul odors from entering the building while allowing wastewater and debris to flow through.
Here’s a video of how plumbing traps work
- You can install plumbing traps in fixtures like sinks, toilets, bathtubs, showers, and floor drains.
- Other than design and function, plumbing traps may differ in materials. You can get them in PVC, ABS, cast iron, or brass.
- To qualify as a plumbing trap, there are requirements for the depth of the water seal.
- Essentially, the liquid seal should have a minimum depth of 2 inches (50mm) and a maximum depth of 4 inches (100mm) to prevent self-siphonage.
Guide to the Different Types of Plumbing Traps
There are 15 different types of drainage traps. That includes
1. Floor Trap or Nahani Trap
As the name implies, this trap installs below your floor to collect wastewater. They’re primarily for areas with a high risk of water overflow, like basements, bathrooms, and laundry rooms. Typically, a floor trap would include a removable grate for trapping solid waste while allowing waste water to pass through freely.
2. Gully Trap or U-Trap
You’ll usually find a gully trap outdoors. Its main role is to collect surface water, more especially from roof gutters and rainwater pipes. Also, it doubles to block debris from entering your drainage system.
A P-trap takes its name from the “P” shape. Nonetheless, it’s more of an inverted “P” with a horizontal arm that connects to a drain pipe in the wall. The P-trap is by far the most common in modern buildings. It typically installs under sinks, showers, and bathtubs.
This plumbing trap is named for its distinct inverted S-like shape. It doesn’t have a horizontal arm like P-traps. Instead, it dips downwards, connecting to a waste pipe on the ground floor.
The “S” shape allows it to function effectively even with low water pressure. Nevertheless, S-traps tend to siphon water out of the trap, leading to an unpleasant odor. It’s for this reason that you’ll mostly find it in older homes or properties. Also, it’s essential to note that most building codes no longer permit using S-traps.
It takes its name from the small letter “q” shape. It’s a modern design that tends to hold a larger volume of water. You’ll generally find Q-traps in the upper-story water closets and shower areas.
6. Bottle Trap
Think of a bottle trap as a space-saving variant of a P-trap. In fact, it’s the best alternative where there’s no sufficient space under basins and sinks for a P-trap. Regardless, a bottle trap may be prone to clogging due to its small size. Even then, it has a removable bottom section for easy cleaning and maintenance.
7. Intercepting Trap
You’ll typically find an intercepting trap outdoors, more especially in the last manhole. Its primary role is to prevent sewage contamination in areas where large volumes of wastewater are discharged, such as industrial sites.
As the name suggests, it intercepts and holds back any solids before they enter a larger drainage system. Unlike typical drainage traps that have a seal of 50mm, the seal of an intercepting trap is deeper, often 100mm.
8. Grease Trap
This plumbing trap intercepts grease and oil from entering the public sewage system. You’ll often find a grease trap in restaurants and industrial setups where large amounts of oil can overwhelm the septic tank.
There are two types of grease traps. A typical grease trap for a low-volume flow of up to 50 GPM and a grease interceptor for large-scale establishments with a high-volume flow of at least 50 GPM.
9. Drum Trap
The Drum trap is an older design. It works on the same principle as a P-trap. But instead of a small dip, it has a large cylindrical vessel to contain water and create a seal against sewer gas.
However, the problem with this design is that water doesn’t move as fast through the trap. For this reason, more solids tend to accumulate at the bottom, leading to blockage and difficulties in cleaning.
10. Bell Traps
As the name suggests, it has a bell-shaped design to collect wastewater. You’ll typically find bell traps installed on the floor of areas that need floor drainages, like the garage and basement.
However, bell traps have a tendency to clog due to the built-in strainer. For this reason, you’ll often find them in older homes. Also, we don’t recommend a bell trap for your bathroom and kitchen as it doesn’t provide adequate protection against sewer gases.
11. Running Trap
A running trap is quite unlike the others on the list. It’s often installed where a drain line rises above the overflow level of a fixture and then drops back down to meet with another drain line. It creates a trap with flowing water instead of standing water like most other plumbing traps.
12. Silt Trap
You’ll often find silt traps in areas with a high risk of sediment buildup, such as near construction sites. It’s also common in homes with older pipes.
Essentially, it’s installed on the main water supply line. Its role is to trap any sediment that enters your system before it can reach your faucets or other appliances.
13. Building Trap/House Trap
Think of a house trap as a barrier between your home’s main sewer line and the public sewer system. Its primary purpose is to prevent sewage gases from entering your home’s living spaces. A house trap typically has two compartments separated by a U-shaped pipe.
14. Straight-Through Trap
As the name implies, it has a straight-through design with no U-bend, allowing water to flow directly through without any deviation. It’s common in kitchen sinks and other applications where a conventional U-bend would not fit.
15. Low-Level Bath Trap
This plumbing trap is primarily for bathtubs and shower stalls. The unique design of this trap ensures that water remains in the trap even when your drain is partially clogged. Apparently, the goal is to prevent any potential flooding or water damage.
Types of Prohibited Plumbing Traps
The most common prohibited plumbing trap is the “S” trap, which is outlawed by both major U.S. plumbing codes. Other prohibited traps are bell traps, crown-vented traps, drum traps, moving parts traps, and non-integral traps.
Here the table below shows the list of banned traps and the reasons behind prohibition.
|Trap Type||Reason for Prohibition|
|S-trap||Prone to siphonage|
|Bell trap||Potential for clogs with no reliable seal|
|Crown-vented trap||Prone to self-siphonage|
|Drum trap||Prone to clogging and can be difficult to service|
|Moving parts trap||Prone to mechanical failures, which may lead to plumbing issues|
|Non-integral traps||Lack of durability and reliability due to cheap materials and poor design elements|
Some codes may allow for the repair of these plumbing traps. However, our advice is to replace them with a more modern and safe trap design.
Tips for Maintaining Your Plumbing Traps
You shouldn’t overlook regular maintenance. This is to avoid costly repairs and ensure proper functioning. The essential trap maintenance plan should include:
- Regular cleaning: Removing all debris, sediment, and build-up from the trap itself, as well as any connecting pipes. You can remove the trap and manually clear any build-up or use specialized trap cleaners designed for this purpose.
- Inspection: Regular inspection of your plumbing traps can help you identify potential issues before they become costly headaches. Check for signs of wear or damage in the trap itself or any connecting pipes.
- Use of proper chemicals: When cleaning your plumbing traps, it’s important to use safe and effective chemicals to avoid damaging the trap or the surrounding pipes.
- Proper venting: Without proper ventilation, water flow through the trap can be slowed down, leading to standing water and unpleasant odors.
- Run water regularly: The trap will dry out if you don’t run water through it. This will break the seal and cause sewer gas to rise in your home.
We examine popular questions related to the types of plumbing traps.
A good trap should maintain an efficient seal, be self-cleaning, and provide unobstructed water flow. Also, it should have a means of access for cleaning and maintenance purposes.
Plus, the water seal should comply with a minimum depth of 2 inches and a maximum of 4 inches.
Gully traps come in two diameters of 300mm and 450mm. The 300mm version typically has a depth of 600mm. On the other hand, 450mm gullies offer two depth options of 750mm and 900mm.
You should space your gully traps 40-50 meters apart.
From our analysis, there are 15 types of plumbing traps. Each offers distinct benefits and limitations. Plus, each plumbing trap is designed for specific purposes. Essentially, these should help you choose the right trap for your home.
However, you should also weigh in on the plumbing codes of your area. After all, some plumbing traps are prohibited in certain states. Also, be mindful of regular maintenance to ensure your plumbing trap is in good function.