The Importance of Backwater Valves in Commercial & Industrial Systems

In the world of plumbing, there’s a golden rule that every professional knows—sewage flows downhill. In reality, it should be, “Sewage only flows downhill until it doesn’t.”

There are situations that gravity can’t handle, such as when city sewers back up during storms. Without proper protection, sewage can find its way back into buildings, causing damage, health hazards, and a mess that no one wants to deal with, and that’s where backwater valves come in.

Backwater valves function as a one-way gate, allowing waste to flow out while blocking any unwanted reverse flow. They are important but often overlooked by those professionals who believe sewage only flows downhill.

Understanding backwater valves, such as when they’re needed, how they work, and how to maintain them, is essential for anyone involved in building design, construction, or maintenance.

When Backwater Valves Are Needed

While we can all agree that having sewage flowing back into a building is terrible and backwater valves are a suitable fix, understanding when and why they’re needed can be confusing.

The basic rule is simple. If your plumbing fixtures are lower than the lid of the next manhole up the street, you need to install a backwater valve. Why is this?

If your fixtures are higher than the manhole lid, any backed-up sewage will overflow onto the street before it reaches your building. However, if your fixtures are lower, that sewage could find its way into your building instead, thus the importance of the backwater valve in this situation.

You might ask, “Why not better safe than sorry and just put them in regardless of the fixture height in relation to the manhole cover?” Interestingly, unnecessary valves could potentially create problems with the proper functioning of the overall system. By not allowing backwater valves for higher fixtures, building codes ensure that the plumbing system remains as simple and effective as possible, reducing the risk of unnecessary complications or failures.

Types of Backwater Valves

Each backflow valve type has pros and cons regarding operation, maintenance, and installation requirements. The choice often depends on the specific plumbing setup, the level of protection needed, and local code requirements.

Manual Valves

These valves are operated by hand using a wheel handle. While not many people’s first choice, they do have their benefits. First, they are easier to install and with fewer moving parts are less likely to have mechanical failures.

Key limitations include:

• Someone must be aware of the backup.
• Someone will need to have access to the valve during flooding.
• That someone must close the valve (and won’t be happy about having to do so).

The best use cases are in buildings with maintenance staff who can regularly monitor and inspect the valve, or in areas with predictable flooding risks, such as heavy rain events.

Automatic Valves

Two of the most common automatic valves are the flap gate and knife gate. The flapper style operates like a one-way door, automatically preventing backflow. The downside is that it may trap waste flowing out, requiring frequent maintenance. Some engineers shy away from the blade-style gate because it seems more complicated, but they are surprisingly simple and use basic physics (water pressure and air compression).

That said, not all knife-edge gates are the same and quality manufacturing is key. For example, Smith’s Flood-Gate ® Automatic Backwater Valve uses a full-port design, meaning it has no enlargements or restrictions in the pipe, the internal diameter matches the pipe exactly when open, and it allows unrestricted flow during everyday use. This valve is entirely automatic. No electricity is required because it uses the backpressure (force) of the backup itself to raise the knife gate, and the blade can easily cut through normal sewage debris and forms a positive seal. Plumbers like it because it has no offset construction issues (inlet and outlet are on the same plane), is easy to retrofit in existing lines, is less likely to get stuck open from debris, and does not require modification to downstream pipe slope.

Single Point-of-Use Valves

Typically, these are floor drains with integral backwater valves that use a ball float to ensure wastewater doesn’t enter the room.

Design Considerations

When incorporating backwater valves into a plumbing system, several crucial design considerations must be made. These factors ensure the valve’s proper functioning, ease of maintenance, and overall effectiveness.

Separating Protected & Unprotected Fixtures

One of the primary design tasks is to separate fixtures that need protection from those that don’t. As we covered above, it’s pretty simple. For example, in a building where the first floor is slightly below the next upstream manhole, the floor drains, mop sinks, and showers on the first floor should be protected. Toilets, lavatories, and sinks on the first floor (which sit higher) might not need protection. All fixtures on upper floors should bypass the backwater valve.

Routing Challenges & Solutions

Separating protected and unprotected fixtures can lead to routing challenges. You want to avoid crossing lines, which may lead to lower inverts. Where lines must cross, you want to route the unprotected line below the line going to the backwater valve. You should also consider using separate stacks for protected and unprotected fixtures. In retrofit situations, creative re-routing may be necessary to incorporate a backwater valve.

So, what are some solutions to these challenges? Well, the most obvious is to plan for parallel drain lines. Where gravity flow isn’t possible, you might consider incorporating lift stations. Finally, carefully planning pipe slopes allows you to maintain proper flow while accommodating the valve.

Invert Considerations

The invert, or lowest point of the pipe’s interior, is crucial in backwater valve installation. Flapper style devices typically require an invert difference of a few inches from inlet to outlet, which means careful planning of pipe slopes as sufficient slope must be maintained leading to and from the valve to ensure proper drainage. A longer “tailpiece” (the pipe section after the valve) is necessary for float-type valves to allow enough sewage rise for valve activation. Retrofit installations present additional challenges, often requiring adjustments to existing pipe slopes or even lowering drainage system sections to accommodate the valve adequately. These considerations are essential for ensuring the valve’s effectiveness and the system’s proper functioning.

Access Requirements for Maintenance

Proper access for maintenance is often a code requirement, but more importantly, it’s pretty darn convenient. You want the valve located where it can be easily accessed for cleaning and repairs. For manual valves, ensure the access panel is not in an area prone to flooding. If the valve is below a basement floor, consider placing it at the bottom of the stairs or on an elevated pad. Provide sufficient clearance around the valve for tools and maintenance work. Extension sleeves or access wells may be necessary if the valve is deep.

Remember, the goal is to design a system that works effectively and can be maintained easily over the long term. Proper planning in the design phase can prevent costly repairs and modifications later.

Backwater Protection in Special Applications

In these unique applications, backwater valves are viewed as one tool among many for preventing backflow. The document stresses the importance of holistic system design, proper sizing, and appropriate pipe slopes over an overreliance on backwater valves. Each application requires careful analysis of potential flow rates and system interactions to determine where and if backwater valves are necessary.

Storm Drain Systems

• Backwater valves may be necessary for area drains in first-floor atriums connected to storm drains, as these can experience backflow similar to sanitary sewer connections.
• Window wells and areaway drains often require backwater protection to prevent water intrusion during storm surges.
• Some authorities require backwater valves to separate sub-soil drains from areaways and floor drains in storm systems.

Emergency Floor Drains

• Backwater valves on emergency floor drains can serve as a tertiary level of protection, safeguarding against failure of primary systems like sump pumps.
• However, backwater valves in these systems are sometimes incorrectly used, emphasizing the importance of proper system design over reliance on valves alone.

Subterranean Parking Garages

• While backwater valves can protect various components of a subterranean garage’s drainage system (such as air intake shafts), we recommend using them sparingly in these complex systems.
• Proper pipe sizing and slope prevent backflow issues more than relying solely on backwater valves.
• In the case of sump pump systems, which often integrate multiple water sources (including sub-soil drainage), backwater protection might be considered for individual components, but overall system design is paramount.

Keys to Success with Backwater Valves

Backwater valves are important, but you shouldn’t overuse them. It’s best to use them only when needed. Good plumbing is about more than just valves. You need to size pipes correctly and ensure they slope correctly. This helps water flow properly. In extensive systems, you must consider how much water comes from all sources.

Getting the design and installation right is crucial. You have to follow building codes, but you also need to think practically. Each building is different, so you must plan carefully. The goal is to create a system that works well and follows the rules. It should protect against sewage backup without causing new problems.

If you do all this, you can make sure backwater valves do their job well. This keeps buildings safe from sewage backflow for a long time.

For more information about our line of backwater valves, visit Smith backwater valves and traps. You can also reach out to our engineers or contact your local Smith representative.