Vaillant mechanical check valve with reducer, Ø 80/110 mm

Product detailed description

Vaillant mechanical non-return valve with Ø 80/110 mm reducer – cascade protection with different connection diameters

Code 0020258990 refers to a mechanical non-return valve with an integrated reducer from 80 mm to 110 mm diameter. This variant combines two functions in a single component: it ensures one-way flue gas flow and prevents backflow into an inactive boiler in a cascade connection, while also connecting the boiler outlet with the smaller 80 mm connection diameter to a common flue gas collector branch of a larger 110 mm diameter. It is therefore a tailor-made solution for situations where a specific boiler in a cascade has a different flue gas connection diameter than the main collector line.

Why the combination of a valve and reducer is practical

When designing cascade boiler rooms, it quite often happens that individual condensing boilers have an 80 mm flue gas connection (typical for smaller and medium output ranges), while the common flue gas collector line, sized for the sum of the outputs of all connected sources, must have a larger diameter – in this case 110 mm. Without an integrated reducer, a separate reducing piece and a separate non-return valve would need to be installed in the line, which extends installation time, increases the number of joints (and thus potential leak points), and takes up more space in what is often already a cramped boiler room. The combined component solves all of this in one compact part.

Technical operating principle

As with a classic non-return valve without a reducer, the operating principle here is based on a movable flap that opens under the pressure of flue gases from the operating boiler and closes under its own weight or spring force once the boiler stops running. This reliably prevents flue gases from other, currently running boilers in the cascade from being pushed back through the common branch into the switched-off source and potentially escaping into the boiler room. The integrated reducer section smoothly transitions the diameter from 80 mm on the boiler side to 110 mm on the collector branch side without unnecessary edges or abrupt cross-section changes, which would otherwise cause increased pressure loss and turbulence in the flue gas flow.

Typical application scenarios

• Mixed cascades – assemblies combining boilers with different outputs and thus different flue gas connection diameters, connected to a single common branch of larger diameter,
• Expanding an existing cascade with a smaller boiler – if a boiler with an 80 mm connection diameter is added to an already operating boiler room with a 110 mm main branch, this component allows direct connection without additional reducing components,
• Apartment buildings with a shared LAS shaft – where boilers of different output ranges may be installed in different apartments, all discharging into a single shared air-flue shaft of uniform diameter,
• Commercial and industrial boiler rooms – with multiple boilers of different output classes connected to a single flue gas collector system.

Installation

The component is installed directly on the outlet of the boiler's flue gas connection, with the 80 mm side connected to the boiler and the 110 mm side facing the common collector branch. As with a classic non-return valve, it is essential to observe the correct flow direction marked on the body of the component – incorrect orientation of the part would prevent the valve from functioning properly as well as the smooth transition of the reducer. Installation should be carried out by a qualified professional as part of the overall implementation of the cascade connection, taking into account the design documentation specifying the exact location and orientation of the component in the flue gas path.

During installation, sufficient space must also be ensured for future access to the valve, in order to check the free movement of the flap and to clean any condensate deposits that may gradually accumulate on the internal surfaces of the reducer and valve during operation.

Safety significance in cascade systems

Like a standard non-return valve without a reducer, this variant also performs a key safety function – it prevents flue gases from operating sources from flowing back through the common flue gas path into a switched-off boiler and from there into the boiler room, when multiple boilers are cascaded onto a common flue gas path. This function is especially important in mixed cascades with different connection diameters, where differences in the operating pressures of individual boilers may be more pronounced, and thus the risk of uncontrolled backflow without a valve is higher.

Material and durability

Like other flue gas path components of Vaillant condensing boilers, this component is made of materials resistant to acidic condensate (pH approximately 3.5 to 5.5) generated by the condensation of water vapor from flue gases, as well as to the operating temperatures of flue gases typical of condensing technology. This resistance is essential for the long-term functionality of the movable flap and the sealing surfaces of the reducer section, without the risk of corrosion or material degradation.

Compatibility

The component is designed for cascade and collector flue gas systems of Vaillant condensing gas boilers with an 80 mm flue gas connection diameter, connected to a common collector branch with a diameter of 110 mm. Before ordering, we recommend verifying the exact diameters on both sides of the connection according to the design documentation of the specific cascade, as Vaillant offers several combinations of reducing non-return valves for different diameter combinations.

Maintenance

A regular annual inspection is recommended as part of the boiler room service check, focusing on the free movement of the flap, the integrity of the sealing surfaces, and the absence of excessive condensate deposits in the reducer section, which, due to the change in diameter, may be more prone to accumulating deposits than a straight section of pipe. If reduced flap mobility or visible damage is detected, we recommend replacing the component immediately, as it is a safety element with a direct impact on protecting the entire cascade against flue gas backflow.

Advantages of the combined component over separate components

Using a single combined component instead of a separate reducer and a separate valve brings several practical advantages: fewer joints in the flue gas path (and thus lower risk of leaks), simpler and faster installation, space savings in the boiler room, and generally a lower overall pressure loss compared to a series connection of two separate components. From a cascade design perspective, it is also easier to work with a single defined component instead of a combination of two separate parts with their own technical parameters.

Relation to cascade sizing

When designing a mixed cascade with different connection diameters for individual boilers, it is essential for the flue gas path designer to take into account the pressure loss of this combined component (reducer plus valve) in the overall chimney sizing calculation, together with the pressure losses of other components in the path. Underestimating this pressure loss may result in one of the boilers in the cascade being unable to reach its rated output due to insufficient reserve capacity of its flue gas fan to overcome the resistance of the flue gas path.

Frequently Asked Questions (FAQ)

Can this component also be used in reverse, i.e. from 110 mm to 80 mm towards a boiler with a larger connection?
The component is designed for a specific flow direction and reducer orientation corresponding to connecting a boiler with a smaller 80 mm diameter to a collector branch with a diameter of 110 mm. For the opposite configuration, we recommend consulting technical support for the correct type of component.

Is this reducing valve required for every boiler in a mixed cascade?
Yes, a non-return valve is generally fitted at the connection of each individual boiler to the common branch, with the type of valve (with or without a reducer) selected according to the flue gas connection diameter of the specific boiler.

Does the diameter reduction affect the boiler's output?
The diameter reduction itself, when the entire flue gas path is properly sized by the designer, has no negative impact on the boiler's output – it is important that the pressure loss of this and other components is already taken into account during the cascade design phase.

How often should the function of this valve be checked?
An inspection is recommended as part of each annual boiler room service check; for cascades with intensive operation, more frequent checks may be recommended by the servicing organization.

Can this valve be purchased separately when replacing a damaged unit in an existing cascade?
Yes, the component can be ordered separately as a replacement part for an existing installation, without the need to change other parts of the flue gas path.

Is this valve also suitable for cascades with more than two boilers?
Yes, its use is not limited to two-boiler assemblies – it is also used in larger cascades with three, four, or more boilers, always depending on the specific combination of flue gas connection diameters of the individual sources in the given project.

Comparison with a separate reducer and separate valve

Customers and designers sometimes consider using a separate Ø 80/110 mm reducer connected in series with a separate Ø 110 mm non-return valve instead of this combined component. This alternative is technically possible but has several practical disadvantages: it requires two separate joints instead of one, i.e. two potential leak points instead of one, takes up more space along the length of the path (which can be a problem in cramped boiler rooms with limited height or length for routing the flue gas path), and generally results in a somewhat higher overall pressure loss due to two separate changes in flow geometry instead of one smoothly integrated reducer. The combined component is therefore, in most cases, a more practical and reliable choice, especially for new installations where the boiler room's spatial layout allows the optimal solution to be selected already at the design stage.

Impact on the acoustics of the flue gas path

A change in pipe diameter can also have a slight effect on the acoustic manifestations of flue gas flow, as a sudden change in cross-section can, under certain circumstances, cause a slight increase in flow noise compared to a straight section of constant diameter. The smooth reducer design integrated directly into the body of this component is designed to minimize this acoustic load compared to a sharp, abrupt change in diameter, which is another practical argument in favor of using the original combined component instead of an improvised solution made up of common reducing fittings.

Connection with regular servicing of a cascade boiler room

In cascade boiler rooms with multiple sources of different output ranges, it is common practice for the servicing company to carry out a regular annual inspection of all boilers in the cascade at the same time, including checking all installed non-return valves and reducer components, regardless of which specific boiler is currently undergoing scheduled servicing. This approach makes it possible to more effectively detect any discrepancies in the functionality of individual flue gas path components as a whole, since a malfunctioning valve can also have consequences for the operation of neighboring boilers in the cascade.

Summary

The Vaillant mechanical non-return valve with Ø 80/110 mm reducer is a practical and space-saving solution for mixed cascade connections of Vaillant condensing boilers with different connection diameters. It combines the safety function of protection against flue gas backflow with a smooth transition in pipe diameter, thereby simplifying installation and reducing the number of potential leak points compared to using two separate components.

Replacement issues during cascade modernization

When modernizing an older cascade boiler room, where one or more original boilers are being replaced with new models with a different flue gas connection diameter, it may also be necessary to replace the original non-return valves with variants featuring the correct combination of diameters matching the new configuration. This is a good opportunity to check the condition and functionality of the valves on the remaining, unchanged boilers in the cascade, since replacing one source is also a good opportunity for a comprehensive review of the entire flue gas path and its components, not just the replacement of the directly affected component.

Note on design documentation and the inspection log

As with other safety elements of the flue gas path, we recommend recording the exact type, position, and orientation of this combined component in the cascade's design documentation and in the flue gas path inspection log. This will make it easier for the chimney sweep during the regular mandatory inspection and for the service technician during any future intervention in the system, especially if the boiler room is taken over in the future by a different servicing organization than the one that carried out the original installation.

Safety aspect from the perspective of flue gas concentration in the boiler room

Leakage of flue gases from a running source into a switched-off boiler through the common flue gas path without a functioning non-return valve may not be immediately apparent, since most modern boilers are equipped with their own safety sensors (such as a flue gas sensor or thermal fuse) that only react once certain parameters are exceeded. However, this does not mean that no flue gas escapes into the boiler room through leaks in service openings or flanges of the switched-off boiler until then. This is precisely why a functioning non-return valve at every connection in the cascade is an essential preventive safeguard, not merely a formal part of the project that can in practice be "bypassed" without visible consequences in the short term.

Summary of the technical advantages of this specific component

In summary, the main benefits of this combined component are: reliable protection against flue gas backflow in mixed cascades with different connection diameters, space savings and fewer joints compared to a solution with a separate reducer and separate valve, a smooth diameter transition minimizing additional pressure loss and flow noise, and full material resistance to condensate and operating temperatures typical of Vaillant condensing technology.

Ordering recommendation for installation companies

When ordering this component, we recommend that installation companies always verify that both diameters (80 mm on the boiler side, 110 mm on the collector branch side) match the specific cascade project before installation, as substituting a component with a different diameter combination would cause delays on site while waiting for the correct part. This step is especially important in mixed cascades, where several different types of reduced and non-reduced non-return valves may be used simultaneously on a single site, depending on the specific combination of boilers, and mixing up parts between individual connections could lead to unnecessary complications and loss of time directly during project implementation.