Check valve DN 110 vs. DN 160 vs. DN 200 – comparison of usage

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Backflow Valve DN 110 vs. DN 160 vs. DN 200 – Comparison of Practical Use

When a customer comes with a request for a backflow valve, one of the first questions is always the same: "What diameter do I actually need?" It seems simple – after all, it is enough to measure the pipe and buy the corresponding size. In practice, however, it is not that simple. The choice between DN 110, DN 160, and DN 200 depends not only on the physical diameter of the pipe, but also on what flows through it, what the slope of the pipe is, whether it is a residential or industrial building, what flow is expected, and where exactly the valve will be installed. Let's look at this systematically, with real examples from practice.

What does "DN" mean for sewer check valves and why it matters

DN is an abbreviation from the French Diamètre Nominal – nominal diameter. In sewer pipes, this dimension indicates the internal diameter in millimeters, although depending on the manufacturer and material, the actual dimensions may vary slightly. For standard PVC sewer pipes, a pipe marked DN 110 has an outer diameter of about 110 mm and an inner diameter of approximately 103–105 mm. A DN 160 pipe has an outer diameter of 160 mm and a DN 200 pipe has an outer diameter of 200 mm.

A backflow valve must fit precisely to the diameter of the pipe into which it is installed. If the valve does not fit tightly, you risk both leaks and the fact that the valve will not close reliably under back pressure – and then the entire protection against backflow is zero. The diameter is therefore not just a number on a label, it is a key safety parameter.

Where DN 110, DN 160 and DN 200 are commonly used – overview

Before we get into the detailed comparison, let's look at where each of these dimensions typically occurs. From the experience of decades of customer orders, we can roughly divide it like this:

DN 110 – internal sewerage in single-family homes, toilet discharge, washing machine discharge, bathtub/shower tray discharge (when using a vertical collection pipe), horizontal connections of individual sanitary fixtures
DN 160 – sewerage from a larger floor, collection pipe in apartment buildings with a small number of apartments, drainage connections for basement drainage, garden drainage systems
DN 200 – main sewer collection in apartment buildings, industrial buildings, larger restaurant/food service operations, larger drainage systems, connections to public sewerage where technical standards require it

This is of course only an approximate overview. Reality is always more complex and depends on the specific project. We will address this topic in more detail in the article What DN diameter do I need for a sewer backflow valve?, where you will also find capacity calculation tables.

DN 110 – valve for a standard household

Diameter DN 110 is by far the most common size of backflow valve in single-family homes. If a customer has a problem with backflow from a toilet, washing machine or sink in the basement, it is most often a DN 110 pipe. This pipe has sufficient capacity to discharge waste from a standard sanitary fixture, and with the correct slope (minimum 2 %, ideally 2.5 %), it can handle the peak discharges of modern washing machines (draining 60–80 liters in a few minutes).

Sewer backflow valve inline DN 110 is typically installed on a horizontally laid pipe in the basement, before discharging into a vertical collection stack or directly before a manhole. Its advantage is the compact size – the valve does not take up much space and can be installed even in space-restricted conditions, such as a low ceiling in a basement or a narrow technical room.

Typical applications of DN 110 in practice

Protection of a toilet in the basement of a single-family home – the most common case in customer practice
Protection of a washing machine located in the cellar or basement
Protection of a shower tray drain in a basement bathroom
Connection to waste from sinks in a basement kitchen (when the sink drain is raised to DN 110)
Protection of a floor drain manhole in a garage, where the floor drain is connected to the sewer

From practice, I know that many people underestimate the need for backup and buy only one valve for the main toilet, forgetting the washing machine. However, a washing machine in the cellar is just as vulnerable to back pressure as a toilet – and a flooded cellar full of dirty sewer water is unpleasant regardless of where the water came from. A good rule is that with DN 110 pipes, you can install valves in series – each device gets its own protection.

It is also important to think about where to place the valve in relation to the manhole. If you have a manhole with manhole cover 315, keep in mind that the valve must be accessible for cleaning and inspection – ideally from the surface through this cover. Valves buried without access are a source of problems during every major storm.

DN 160 – a transitional size with a wide range of applications

Diameter DN 160 is less common in everyday practice than DN 110 or DN 200, but it has its own place. It is a kind of "transitional" size that appears in situations where DN 110 is not sufficient in capacity, but DN 200 is unnecessarily large. In sewer systems of single-family homes, DN 160 is encountered mainly in the following cases:

Collection horizontal pipe that carries waste from several toilets, bathrooms and kitchen at once (for example, in a larger single-family home with two bathrooms and a basement)
Connections of garden drainage systems, where a larger amount of rainwater and groundwater needs to be discharged
Connecting pipes between manholes in drainage routes
Sewer connections of smaller apartment buildings (3–6 apartment units)
Drainage systems of parking lots or access areas

It is interesting to note that DN 160 often appears in practice precisely in drainage. The customer wants to protect the basement from rising groundwater, has a drainage system built around the foundation and a drainage manhole – and the connection of this manhole to the sewer is exactly DN 160. In such a case, a DN 160 backflow valve is not only suitable, but actually necessary. Without it, during heavy rain and a clogged sewer, water would be pushed back through the drainage directly to the house foundation – which is exactly the scenario you want to avoid.

It is also important to know that the check valve DN 160 is physically larger than DN 110, and therefore requires more space during installation. The inspection opening must be appropriately sized – when placing it in a manhole, consider whether your manhole and its cover are suitable. The topic of selecting the right manhole size is discussed in the article Manhole Cover 315 or 400 – How to Choose the Right Size?

DN 200 – valve for larger buildings and main drains

The check valve DN 200 is a size that is encountered less frequently in single-family homes, but it is practically standard for larger buildings. Sanitary check valve DN 200 is used primarily where it is necessary to protect the main sewer line – that is, at the location where drainage branches from several apartments, floors, or businesses converge.

Where DN 200 is used in practice

Apartment buildings – main sewer connection of an apartment building with 8 or more units, where the diameter is determined by calculation according to STN EN 12056
Buildings with high drainage capacity – restaurants, canteens, hotels, large-scale kitchens
Industrial buildings – production halls, warehouses with cleaning stations, car washes
Main rainwater drainage for larger paved areas (parking lot, shopping center)
Inspection manholes on the main sewer line before connecting to the public network

From practice: during the reconstruction of an apartment building in Bratislava, we dealt with a case where the basement areas of a 12-unit apartment building were regularly flooded by backflow from an overloaded public sewer system during heavy rain. The original solution – two DN 110 valves on the basement WC – was completely ineffective, as the main surge came through the DN 200 connection. The correct solution was a DN 200 valve on the main connection pipe, supplemented by a manhole with the appropriate cover. For inspection and maintenance of this valve, a 400 manhole cover was used – large enough to allow a hand to be inserted into the manhole and the valve to be inspected without excavation.

DN 200 valves are physically large – the total length of a DN 200 check valve is approximately 400–500 mm including the flange and body. Therefore, it is necessary to plan sufficient space for installation and access to the inspection cover in advance. Unlike DN 110 valves, where the cost of the valve is relatively low and customers sometimes buy them preventively "just to be safe", DN 200 valves represent a larger investment and a more significant intervention into the piping – so the choice of size must be well justified and not underestimated.

Comparison DN 110 vs. DN 160 vs. DN 200 – summary table

Parameter	DN 110	DN 160	DN 200
External pipe diameter	110 mm	160 mm	200 mm
Estimated internal diameter (PVC)	~103 mm	~150 mm	~188 mm
Pipe cross-section (cm²)	~83 cm²	~177 cm²	~278 cm²
Flow capacity at 2 % slope	~4.9 l/s	~10.4 l/s	~16.1 l/s
Typical use	WC, washing machine, bathroom in a single-family house	Drainage, collection from multiple devices	Apartment buildings, commercial buildings
Installation – complexity	Low	Medium	Higher
Space requirements	Low	Medium	High
Access for maintenance	Simple	Medium	Manhole or inspection opening required
Recommended manhole / cover	Manhole 315	Manhole 315 or 400	Manhole 400 or larger

Pitfalls customers run into – real examples from practice

Case 1: Customer confuses outer diameter with DN

One of the most common problems we encounter: the customer goes to measure the pipe, reads the numerical dimension with a caliper and comes up with a number, for example 113 mm. Then he buys a flap because "it is close to DN 110". However, the pipe he measured was a PP-HT pipe with an outer diameter of 110 mm and a different neck dimension than PVC. The flap does not fit. Solution: always identify the material and pipe system and work with DN according to the manufacturer, not with the measured outer diameter value.

Case 2: Customer installs a DN 110 flap on a pipe where drainage also flows

In practice, we encounter cases where a DN 110 pipe (intended primarily for WC) is connected by the customer to a drainage pipe from the foundation area. During heavy rain, the flow is higher, the flap cannot close in time, or on the contrary, the flow pushes the flap with a force that deforms it. The solution is clear – for combined (sewage + drainage) piping, use a larger diameter, at least DN 160, or handle the situation separately.

Case 3: Customer installed a DN 200 flap instead of DN 110 "just to be safe"

The customer's logic was: the bigger, the better protection. In reality, flaps work on the principle of a float that is lifted by the water flow. If a DN 200 flap is mounted on a DN 110 pipe via a reducer, the inflow is not sufficient to reliably open the flap and the float can get stuck in a half-open position. Result: waste flows poorly, sags and clogs occur. The flap must match the actual pipe diameter.

Hydraulic calculations – how to find out if your capacity is sufficient

For the average owner of a family house, it is not necessary to perform complex hydraulic calculations – the rules are relatively simple. For customers with larger buildings (apartment buildings, commercial premises), however, the selection of the DN check valve must be based on the calculation of the maximum discharge according to the standard STN EN 12056-2 (Gravity Drainage Systems in Buildings).

The basic formula for calculating the flow in a gravity pipe is based on the Manning-Strickler equation:

Q = (1/n) × A × R^2/3 × I^1/2

where Q is the flow in m³/s, n is Manning's roughness coefficient (for PVC ~ 0.009), A is the cross-section of the pipe in m², R is the hydraulic radius in m and I is the slope of the pipe in m/m. For typical slopes of 2 % to 3 % and material PVC, approximate values are given in the table above.

In practice, this means: if you have, for example, an apartment building with 10 apartments, where each apartment produces ~0.5 l/s at peak (reality is a bit more complex, but roughly), the total peak flow is ~5 l/s. A DN 110 flap with a capacity of ~4.9 l/s is on the edge and insufficient, a DN 160 flap with a capacity of ~10.4 l/s is sufficient. If you add the roof drainage of the apartment building, a DN 200 may be necessary.

A more detailed methodology is explained in the article How to choose the right sewage backflow flap – diameter, type and placement.

Combination of multiple flaps of different DN in one building

In practice, we very often encounter the fact that one building needs flaps of different diameters. This is not a problem – on the contrary, it is the right approach. Imagine a larger family house with two bathrooms, a basement WC, a washing machine in the basement and a drainage system around the foundation:

Basement WC → flap DN 110 on the WC connection
Washing machine in the basement → flap DN 110 on the washing machine connection (or if the washing machine discharge is elevated into a common pipe with the WC, one flap on the common branch)
Drainage around the foundation → flap DN 160 on the drainage connection to the sewer
Main sewer connection (if it is a larger house or a multi-generational house) → flap DN 200 on the main inlet

This multi-level solution is more expensive, but it offers real protection at each level. If one flap fails (clogged, non-functional float), the other flaps still protect the respective devices. It is not unnecessary paranoia – it is a proven practice recommended by insurance companies as well.

Standards, legislation and obligations for the installation of a backflow flap

The selection of the correct diameter of the backflow flap is not only a technical, but sometimes also a legal issue. In Slovakia, the installation of backflow flaps on sewage systems is mainly governed by these standards and regulations:

STN EN 13564 – standard directly dedicated to backflow valves for building drainage systems; sets requirements for construction, testing and marking
STN EN 12056-1 to 12056-5 – gravity drainage systems within buildings; here you will find the calculation basis for dimensioning diameters
Act No. 442/2002 Coll. on public water supply and sewerage – sets the obligations of property owners towards the public network
Local building regulations and conditions of the public sewer operator – some cities and municipalities directly require the installation of a backflow valve as a condition of connection

In practice, we encounter the obligation to install a backflow valve more and more often, especially in flood-prone areas or in locations with overloaded sewer systems. We discuss this in more detail in the article Protecting your home from sewer backflow – when is a flap mandatory?

From the perspective of warranty and insurance claims, it is important that the flap meets the requirements of standard EN 13564 and is from a certified manufacturer. In the case of an insurance incident (flooding), the insurance company may investigate whether the protection was installed correctly and whether it corresponded to the pipe dimension. Installation of an incorrect diameter (e.g. DN 110 instead of the required DN 200) may be a reason for rejection or reduction of the insurance payout.

Practical tips when selecting and purchasing

To conclude this section, a few proven tips from practice that will help you make the right decision:

Identify the pipe material and system: PVC KG, PP-HT, PE – each system may have slightly different neck dimensions. Always buy the flap as part of a compatible system.
Measure the actual outer diameter of the pipe: Do not just guess by eye. A small sliding tape measure costs just a few euros and will save you a lot of trouble with a non-fitting part.
Consider access for maintenance: A backflow flap without access for regular cleaning is only a matter of time before it fails. Plan a inspection opening or manhole even before installation.
Do not combine different systems without reductions: If you feed a DN 125 flap into a DN 110 system, you need the correct reduction – not improvisation with sealing tape.
Flap DN 125 as an alternative: For some applications, there is also a size DN 125, for example sewage backflow flap continuous DN 125. This dimension is used for HT pipes with an outer diameter of 125 mm, especially in German-speaking countries and in some older domestic installations. If you are unsure, check the type of your pipe.
Consider the flap type – continuous vs. end: For most applications, a continuous flap is more versatile. We discuss the difference in more detail in the articles Continuous vs. end sewage flap: what is the difference and where to use which and How to choose the right sewage backflow flap – continuous vs. end.

Maintenance and lifespan of flaps according to diameter

One of the practical differences between different flap diameters is their susceptibility to clogging and the required frequency of maintenance. A simple rule applies here: the smaller the diameter, the easier the flap gets clogged with mechanical impurities (wet wipes, hygiene products, kitchen fat). Flaps DN 110 on the WC are therefore relatively prone to clogging if users do not pay attention to what they flush.

Flaps DN 160 and DN 200 are more robust and mechanically resistant, but their inspection is physically more demanding – especially if they are located in a manhole or in the ground. Therefore, for larger diameters, it is especially important that access to the flap inspection cover is convenient and that the manhole is properly designed.

Approximate recommendations for the frequency of inspection and cleaning:

DN 110 (WC, washing machine): visual inspection once a year, cleaning as needed (at any change in drainage or odour)
DN 160 (drainage, collection): inspection once every 1–2 years, after each major storm
DN 200 (main collection): inspection once a year, ideally before the winter season, or before the expected period of increased precipitation

A detailed cleaning procedure and common faults can be found in the articles Maintenance and cleaning of a sewage backflow flap and Common faults of backflow flaps – why the flap leaks or gets stuck. If you plan to install it yourself, I also recommend reading Installation of a sewage backflow flap step by step.

Most frequently asked questions (FAQ)

Do I need a flap of the same DN as my pipe, or can I use a larger size?

The flap must match the diameter of the pipe it is mounted on. Using a larger flap via a reduction is technically possible, but not recommended – the flap may not reliably open and close at insufficient flow. The flap (closing element) is dimensioned for a specific hydraulic pressure and flow corresponding to the given diameter. Always use a flap of the same DN as your pipe.

Can I connect multiple smaller drain branches to one DN 200 flap at the same time?

Yes, but only if the flap is located after the point of connection of these branches – i.e. it protects the entire connected system. In this case, it is necessary that the total flow of all branches together does not exceed the capacity of the DN 200 flap. If, on the contrary, you want to protect each branch separately (recommended for greater safety), each branch will have its own flap of the corresponding diameter.

Is DN 160 really necessary, or can I always use either DN 110 or DN 200?

DN 160 has its fixed place and is not just a "compromise size". Primarily in drainage around the foundations of houses, DN 160 is the standard size to which drainage manholes and fittings are dimensioned. Forcing the drainage system into DN 110 would mean too small a capacity and a risk of backflow directly around the foundations – which is exactly the opposite of what drainage is supposed to do.

What is the difference between a DN 110 and a DN 125 flap? What should I choose?

DN 110 is the standard size for PVC KG sewage (outer diameter 110 mm). DN 125 is used for HT (high-temperature) piping with an outer diameter of 125 mm, which is commonly used for internal drainage pipes in buildings (vertical risers, WC drains in bathrooms above the basement). If you have internal HT piping, you need DN 125 – a DN 110 flap does not fit into a DN 125 HT pipe. Always check the outer diameter of the pipe with a measuring tool.

What happens if I install a flap of a smaller diameter than my pipe?

A smaller diameter flap simply does not fit into a larger diameter pipe – it is not possible to seat it tightly. If someone were to solve the situation with improvised seals, the risk is double: first, leakage during normal operation, second, the flap does not close the entire pipe cross-section under reverse pressure and water bypasses the flap body. Result – no protection against backflow.

Do I need a permit to install a backflow flap?

Replacement or addition of a backflow flap on an existing pipe inside or in a manhole on the property (not on the public network) does not require a building permit. If, however, it involves an intervention in the house sewer connection, it is advisable to inform the public sewer operator and proceed according to their conditions. Some operators require the intervention to be carried out by an authorized person or to be documented.

Conclusion – choosing the flap diameter is not a matter of chance

The correct choice between DN 110, DN 160 and DN 200 is not just a question of "what pipe do I have at home". It is a decision that depends on a combination of factors: hydraulic capacity, type of protected equipment, position in the system, access for maintenance and sometimes also legislative requirements. Choosing a too small diameter leads to insufficient capacity or a non-functional flap; choosing a too large diameter leads to a hydraulically unreliable flap that does not lift correctly at low flow.

In the vast majority of single-family homes, the situation is solved by the DN 110 flap. For drainage and collection lines, look at DN 160. For apartment buildings and larger facilities, the correct solution is the DN 200 flap. And if you are unsure about the selection – do not measure the pipe only, but map the entire system: where the water flows, where the branches connect, and where the most vulnerable spot is in terms of backflow.

Do you have a question about this topic?

Having trouble deciding or dealing with a specific situation in your home? Write to us – we will be happy to help.