Can AAVs be installed externally / outside?

A commonly asked question is whether Air Admittance Valves (AAVs) can be installed outside. In the UK Part H of the Building Regulations 2010 (clause 1.33) states that “Air admittance valves should not be used outside buildings…” Reasons for this include:

  • Temperature
  • UV degradation
  • Animals/birds/insects
  • Debris

As Part H of the Building Regulations 2010 does not approve external use, a specific third party approval (such as the BBA) is required.

Any AAV marketed for external use must be supported accordingly with an approval which specifically states that that specific model of the product may be installed outside.

If the third party certificate doesn’t list the specific model, and doesn’t specifically state for “external” or “outside” use, then it’s not Part H compliant and installing it would risk rejection by Building Control.

The Studor Maxi-Vent*, however, is uniquely certified by the BBA as being approved for both internal AND external installation. This means that the Maxi-Vent Air Admittance Valve (AAV) may be legally installed outside in the UK when installed in conjunction with the Aluminium Cover, and the BBA approval will satisfy Building Control that the installation is Part H compliant.

Whilst the BBA approval for external installation of the Studor Maxi-Vent was granted in 2013, Studor has been selling the Maxi-Vent for outside installation (in conjunction with the Aluminium Cover) worldwide since 2003 – over 14 years ago!

AI rated (-20°C to +60°C) in accordance with European Standard EN12380, without the insulating cap or Aluminium Cover, the Maxi-Vent is actually independently verified to operate right down to -40°C!

For added protection against UV degradation, the Maxi-Vent is manufactured with a UV stabiliser, and its design incorporates internal and external screening as a barrier to the ingress of debris, animals, insects and birds. The Aluminium Cover may even be painted to match surrounding pipework or brickwork if required.

Maintenance free, and provided with Studor’s standard lifetime warranty, the Maxi-Vent really is the only choice for an external AAV – not only does it uniquely have the required approval for legal installation of an AAV outside, but it is also specifically designed to be robust enough to be installed externally – ticking all the boxes!

*distributed in the UK by Wavin as their OsmaVent 110

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CPD Article: High Rise Drainage Ventilation

The importance of the water trap seal

Being the only barrier between the drainage system and the living and/or working space, it is critical that the water trap seal is maintained at all times. This protects the occupants of the building from the potentially harmful gases and pathogens which within the drainage system. All buildings, regardless of whether they are low rise or high rise, need correct drainage ventilation to allow the essential water trap seals to be maintained.

In high rise and complex drainage systems there is additional stress placed on the water trap seals due to the increased loads into the system, and the distances of the relief of the pressure regime is greater in time and distance in taller buildings.

Negative pressure

Conventional thinking in drainage venting is to deal with the negative pressure. This originates from the studies carried out by Hunter in 1920 (Hunter’s Curve), which only looked at steady state systems. The established thinking is that water trap seals are depleted due to siphonic action. The most common causes are self siphonage and induced siphonage.

Self siphonage

A negative pressure transient occurs when there is a discharge of fixtures to which the water trap seal is connected. This can have the effect of reducing the trap seal (or pulling the trap). This occurs as the momentum acquired by the waste passes through the fixture and down the trap seal. This momentum is transferred directly into the trap seal and trap seal loss occurs – commonly known as “self siphonage”.

Induced siphonage

Other fixtures discharging in the building can also affect the trap seal. This occurs when there is a pressure fluctuation caused by a discharge of another fixture in the system other than the fixture to which the trap is connected. This is commonly known as “induced siphonage”, which is very common in multi-storey buildings.

Maintaining the water trap seal

Plumbing Regulations call for the water trap seal on sanitary fixtures to be maintained at all times. This is accomplished by the introduction of atmospheric air into the plumbing drainage system.

Venting with pipes has limitations, as open vents require penetrations through the roof to allow the atmospheric air to balance the pressure transients within the sanitary drainage system, as well as the requirement for the pipe to carry this air. Research is proving that the current practice of using a 50% smaller vent pipe network is unsafe as this can lead to water trap seal depletion. The only correct and safe way to install a passive pipe vent system is where all vent pipes must be larger than the waste carrying pipes.

Alternatively, Air Admittance Valves (AAVs) can be installed at the “point of need” near the water trap seals that require protection. This has the benefit of eliminating the vent pipe network, the space required, the roof penetrations, and greatly simplifies the design of a large plumbing drainage system.

Positive pressure

Whilst AAVs are very suitable to vent the negative pressures that are generated in the system (particularly with regard to branch venting), special consideration must also be given to positive pressure which occurs typically in high rise buildings. Traditional standards call for relief vents and open stack vents to provide positive pressure relief. “Active ventilation” is an alternative solution which uses a combination of AAVs and the P.A.P.A. (Positive Air Pressure Attenuator).

Active drainage ventilation

The active drainage ventilation principle works by local intervention to remove or attenuate an incoming transient that, if left, would lead to trap seal depletion. This is achieved by placing AAVs and the P.A.P.A onto the standard pipes of the system to limit the surge pressures adjacent to the traps by reducing the rate of local changes in flow conditions. The placement of the AAVs and the P.A.P.A must be positioned between the source of the transient and the base of the stack; offsets are typical points to generate positive transients.  The pipe calculations for loadings and gradients do not change when installing active drainage ventilation, so BS EN12056 can still be used for the sizing of the system.

Active drainage ventilation reduces the effects of the negative and positive transients, balancing the pressure within the drainage system – if the system pressure exceeds +/- 40mm WG (400Pa) the water trap seals can be lost by induced or self siphonage:

  • Negative pressure (transients) are dealt with through the introduction of local airflow using AAVs on the branches. Air is allowed in through the AAV as required, which then seals tight to prevent sewer gases from leaking out into the habitable space.
  • Positive pressure (transients) are absorbed by the P.A.P.A., slowing them down from the speed of sound (320m/s) to a harmless 12m/s, which is then released back into the system to naturally dissipate.

Active venting versus traditional “passive” venting

Active venting should be considered as functionally “superior” over traditional “passive” venting:

  • The removal of long, and possibly, convoluted vent connections to atmosphere reduces the time taken before local relief can be applied – allowing the pressures to be balanced quicker with active venting.
  • Local suppression prevents transient propagation throughout the network prior to relief – removing the risk of the siphonage of multiple traps.

With traditional “passive” venting, reliance on roof penetrating open terminations allows transients to travel the whole system prior to any remedial action. The fundamental issue being that a transient should be dealt with between its source and the first appliance trap seal in order to prevent trap seal depletion.

Scientifically and empirically proven

Extensive research by leading industry academics has repeatedly proven that active drainage ventilation (utilising the combination of AAVs and the P.A.P.A.) protects the water trap seals of high rise buildings without any of the limitations of the “passive” vent pipe solution.

Anyone wishing to see first-hand both systems operating is invited to attend a “Seeing is Believing” test tower demonstration. Located at Studor’s Northampton facility, the test rig replicates the drainage system of a 40 storey building and incorporates valves to switch between an active vented system and a traditional passive vented system. More information and to register:

Written by Steve White, Studor Technical Director

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CPD Article:
Venting External Drainage Systems with Active Carbon Filters

What is an active carbon filter for drainage? It is a two-way vent that uses active carbon as a filter to absorb the sewer gases (primarily hydrogen sulphide H₂S and methane CH4) which come out of a drainage vent.

Due to the common design of active carbon filters for drainage systems, they are restrictive vents, and therefore limited in application to prevent self or induced siponage of traps seals resultant from transient pressures in the drainage system. As such, they do not replace the need for open vents or Air Admittance Valves (AAVs) for venting drainage systems on their own.

The filtersStudor Maxi-Vent AAV with the Maxi-Filtra can be used in combination with AAVs to provide the open vent requirement on the drainage system; the AAV will provide the fast air requirement of the drainage system, and the filter will provide the filtered relief to the slow positive pressure rise out of the drainage vent stack.

The active carbon filters work as an inlet and an outlet, and typically have an airflow of 5 litres per second in both directions at 250Pa (25mm Wg).

Being a two-way vent, the filter must be installed outside the building – the same as for an open vent. Over time the active carbon may become saturated and harmful sewer gases can pass through the filter and into the surrounding air. The filter cartridges typically have a life of over 2 years before needing replacement. High-use systems, or a pumped system, can reduce the life of the active carbon due to saturation. Typically on a domestic septic tank the cartridge is replaced when the tank is emptied of sludge, or there is an increase of sewer smells around the vent. When used for other applications it is recommended that the replacement of the cartridge is placed on a maintenance schedule.

Problem Solving

Active carbon filters are a good solution for solving issues with smelly vent pipes, either on a conventional system or septic tanks. They generally offer an immediate, easy fix solution, being fitted with a push-fit connector.

Wind Effect

Wind affects water trap seals, and can cause traps within the building to self-siphon – this usually occurs when wind gusts are over 35 k/mh. When the wind blows over the stack outlet, the air pressure in the pipe is lowered. This is due to the Bernoulli’s principle (“as the speed of the moving fluid (air) increases, the pressure within the fluid (air) decreases”). The lowered pressure in the pipe creates suction (negative transients) throughout the above ground drainage system. As the wind gusts, this causes the trap seals (typically closest to the open vent) to oscillate and can lead to the trap to self-siphon. We have all seen this occur when it is windy outside and have witnessed the water trap seals move! If the gust causes significant pressure (around +/- 400Pa (400mm Wg)) the water traps seals can be depleted.

If a building is affected by wind effect on a regular basis then an active carbon filter combined with an AAV can be used to cap the stack, and therefore protect the system from the wind effect.

Recirculation of Sewer Gases Back into the building

Part H of the Building Regulations requires that the open vents must be installed to external air at least 900mm above any opening into a building within 3 metres – this could be windows or air handling units. Also, with modern design, roof terraces are becoming more common.

Problems occurs when the vents are located too close to the opening; maybe through renovation work, or change of use. An active carbon filter filters combined with AAVs could be used to solve these issues.

Why Water Trap Seals Need Protecting

Water trap seals are the only barrier between the drainage system and the living space. Typically these have a water seal between 50mm and 75mm, but when subjected to pressures in the system of +/- 400Pa (40mm Wg) the traps can be subjected to siphonage. This removes the barrier, and allows potentially harmful sewer gases to enter the living space.

Sewer Treatment Plants and Septic Tanks

Active carbon filters are an ideal solution to vent the low level outlets on septic tanks. This prevents the need to vent the tanks back though the building, or away from areas around the tank.

As waste discharges in the tank it also draws air. When the tank starts to become full, the capacity of the tank to deal with the waste and the air becomes reduced. This can lead to slow discharges from appliances in the same way as experienced with a conventional system when there is a blockage downstream – the air has to go somewhere!

Providing a vent at the outlet of the tank provides a path for the air to leave the tank so that waste flow into the tank is normal.

The issue occurs with where to place this vent. As smells and sewer gases will come out of the tank, if the vent is at low level then the smells can disturb people in close proximity to it.

By placing the open vent with a longer pipe distance (10 meters) the open vent is less efficient, as the gasses from the tank may head back into the building drainage system, and if there is a depleted trap seal the gas will enter the building. Using an active carbon filter prevents this from happening as it provides a path for the air out of the tank at the outlet at low level, as well as filtering the unpleasant, and potentially harmful, sewer gases.

Maintenance and Ease of Installation

No specialist installation is required for this type of filter. They are commonly installed with a push-fit connector only, so you don’t even need to be skilled to secure the filter in place. They often have a cap which simply lifts off to enable easy access for filter cartridge replacement. In installations with high odour saturation, the carbon filter should be replaced more regularly than the recommended two years, i.e. before or when odour becomes noticeable.

The filters are commonly supplied with one carbon filter and a connector which fits standard UK pipe. An aluminium cover should ideally also be provided, which provides extra protection for the filter when it is installed outside in the open air – added insulation against extreme temperatures (-20°C to +60°C) and protection from animal/birds and the environment, i.e. inclement weather and the sun’s ultra-violet rays.

Written by Steve White, Studor Technical Director

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CPD Article: Introduction to Air Admittance Valves (AAVs)

Introduction to Air Admittance Valves (AAVs)

Whilst there is a growing awareness and knowledge of the ever-increasing risks to health from the drainage system, it is often given little thought – effectively being out of sight and out of mind – despite it being one of the few building systems that is integrated throughout the whole building. The water trap seal is the only barrier between the drainage system and the living and/or working space; it is therefore essential that this is maintained at all times. The loss of a trap seal results in unwanted smells, noise and, importantly, the risk of pathogens/disease spreading from the drainage system into the inhabited space. Whilst these are unpleasant in a domestic environment, there are serious health and safety concerns in a commercial environment, where the building owners, landlords and/or occupiers have a duty of care.

What mostly affects water trap seals?

Drainage venting is all about preventing the system pressure from exceeding -400Pa (40mm Wg), i.e. the pressure at which water trap seals will be affected. This would be mostly due to pressure fluctuations (self siphonage, induced siphonage, positive pressure and wind effect) and thermal depletion.

A negative pressure transient occurs when there is a discharge of the fixture to which the trap seal is connected. This can have the effect of reducing the trap seal (or pulling the trap). This occurs as the momentum acquired by the waste passes through the fixture and down the trap seal. This momentum is transferred directly into the trap seal and trap seal loss occurs. This is commonly known as ‘self siphonage’.

Other fixtures discharging in the building can also affect the trap seal. This occurs when there is a pressure fluctuation caused by a discharge of another fixture in the system other than the fixture to which the trap is connected. This is commonly known as ‘induced siphonage’, which is very common in multi-storey/multi-use buildings.

Key venting components of a drainage system

  1. Trap venting: Venting of a single fixture.
  2. Group venting: Venting of a group of fixtures, using one vent on the wet side of the last fixture.
  3. Branch venting: Ventilating pipe connected to a branch discharge pipe.
  4. Stack venting: Extension of the vertical discharge pipe above the highest branch discharge pipe connection that terminates at an end, open to atmosphere or with an AAV.
  5. Ventilating stack: Main vertical ventilating pipe, connected to the discharge stack to limit pressure fluctuations within the discharge stack.
  6. Drain venting: Venting near the end of a main drain or branch drain, the vent being installed on the wet-side of the last fixture.

A combination of the above can be used on larger projects, but these methods have limitations, as open vents require penetrations through the roof to allow the atmospheric air to balance the pressure transients within the sanitary drainage system.

The larger or more complex the system, the longer it takes for the vent at the top of the building takes to react, leading to depletion of the water trap seals. You know when this occurs by just watching and listening. For example, if you see the water in the WC pulling, or listen to the P-trap gurgling, this is an indication venting is inadequate as the traps are being pulled due to the pressure in the system.

Alternatively, Air Admittance Valves (AAVs) can be installed at the Point of Need (PON), near the trap seals that require protection. This has the benefit of eliminating the vent pipe network, the space required and the roof penetrations.

What is an AAV?

An AAV is a valve that limits pressure fluctuations within the sanitary drainage system by allowing air to enter the system but not to escape. It draws the air, which is required to maintain the trap seals, from the living space where it is installed.

An AAV should open before -75 Pa, allowing air into the system and relieving the negative transient pressure. This keeps the pressures in the system for discharges between 0 and -250 Pa. If the system goes above these pressures, this can lead to the depletion of the trap seals. A typical P-trap will suck dry in less than 1 second if the pressure in the system reaches above -500pa (50mm Wg).

AAVs work by utilizing a reverse lift membrane. When there is water movement in the system the valve will open; when the movement of water stops, the AAV will seal airtight by gravity. AAVs have the effect of slowing down pressure transients in the building and providing air at the PON, eliminating the risk of pathogens leaving the sanitary drainage system and entering the living and/or working space. Most important is that the AAVs are sealed airtight when there is no movement of air in the system.

Critical aspects of an AAV’s operation

  1. The need to respond quickly to changes in pressure, every time.
  2. The necessity to seal completely tight with no leakage whatsoever.
  3. Longevity of operation; as long as the drainage system itself.

What to look for in a good AAV

Choosing the correct AAV is important. In the UK AAVs must conform to BS EN 12380 and must display the correct information and the CE mark. To further ensure that the AAV is of verified appropriate quality, it is recommended that the valves also have a third party accreditation, for example, a BBA certificate or KEYMARK approval. This provides reassurance that the AAV has undergone rigorous testing at an external testing institute and are routinely assessed.

AAVs that utilize springs, O-rings or clip fit lids should be avoided, as these generally inevitably lead to leakage at low pressures.

Under BS EN 12380 AAVs are rated for performance. An ‘A’ rated AAV can be installed up to 1 metre below the appliance’s flood level and a ‘I’ rated AAV has been proven to operate in extreme temperatures from -20°C to +60°C. Having an AAV that meets the AI or the AII classification will ensure the product is of sufficient quality and performance to provide full protection.

AAV Classification under BS EN 12380
Determining Factor Range/Position Designation
Permitted to be located below
flood level of connected appliances
Temperature -20°C to +60°C
0°C to +60°C
0°C to +20°C

Written by Steve White, Studor Technical Director

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When Art Meets Science…

There are times when different disciplines and arts converge with each other to provide outstanding results – the work of the talented Slovenian-born Dr Vesna Petresin, BSc PhD FRSA is one such example, with a lot of the subjects she uses in her visual and sound pieces and performances being inspired by fluid dynamics.

Vesna first met the founders of Studor (STUre and DORis Ericson) when Heriot-Watt University hosted the CIB’s 1999 W062 Symposium on Water Supply and Drainage in Buildings, in which Vesna’s father, Dr Eugen Petresin of the University of Maribor, presented his research. A relationship which has been maintained ever since, with Sture and Doris following her artistic career over the years. Studor was therefore happy to sponsor an audio-visual production of Vesna’s work at the 2017 Transmediale international festival in Berlin as part of the Art Science Node selection, taking place at the German Patent Bureau headquarters.









Vesna’s piece of work titled “The Dreams Our Things Are Made Of” was well-received by leading members of the German science, research & innovation, technology and cultural sectors, along with international guests. The overall show was a great success which resulted in the German Patent Bureau giving the organisations, the Art Science Node, exclusive rights to curate events in their premises both in Berlin and in Munich – a great honour indeed!

Throughout the development of her artistic career, Vesna has also remained involved with her scientific career. Following the 2001 W062 Symposium on Water Supply and Drainage in Buildings, which was organised in Portoroz, Slovenia by Vesna’s parents, her father (Dr Eugen Petresin exchanged research and discussed collaboration with Sture and Vesna herself has been a research assistant to her father and his teams (in Slovenia, UK and Germany), for over 20 years. Since 2003 she has also been a Research Fellow to Cecil Balmond, Deputy Chairman of Ove Arup & Partners and, through this collaboration, she has met research teams that Studor collaborated with at Arups and Heriot-Watt, being an active advocate of Studor’s innovations and products to the engineering teams she has met. More about Vesna’s successful artistic and scientific careers can be read on her LinkedIn profile.

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Studor – the Innovators, not the Imitators!

The foundation for Studor to lead the industry with drainage ventilation technology was laid by Sture Ericson (co-founder of Studor), when he applied for the patent on his first designed Air Admittance Valve (AAV) – the Bjare Valve – in July 1973. Since the inception of Studor in 1975, this foundation has been continually built on, and over 40 years of research has resulted in the application of numerous patents providing protection to Studor products in over 50 countries worldwide.

This guest blog from Laurent Overath, Intellectual Property Consultant for Cabinet Bede (Studor’s appointed patent attorney) comments on the importance of patent protection and of the correct use of trademarks:

Studor always did value technological innovation. The numerous high quality products that have been marketed in the past clearly demonstrates this.

In order to secure these research efforts, key technological innovations have been subjected to patent protection, whereby Studor was granted exclusivity over the marketing of the newly developed technology.

In parallel with the patent protection, covering the “inside” technology of Studor’s products, a brand or trademark registration strategy is maintained, providing Studor exclusivity over the “outside” use of a range of trademarks such as Maxi-Vent® and P.A.P.A.®, in addition to the “house trademark” Studor®.

Provided that registrations are timely renewed, trademark protection can in principle last infinitely. However, where the trademark would not have been used over a certain period of time, registrations may become cancelled.

In case a protection would be challenged on such basis, Studor will be required to produce sufficient evidence of genuine use to avoid that the registration would become cancelled. Genuine use is use made of the trademark in conformity with the standards of the concerned economic sector, i.e. the sector of drainage ventilation.

Use of a trademark can be evidenced through the submission of various types of documents, such as copies of invoices*, sale offers*, advertisements, award certificates, commercial fairs photographs, etc. (*can be partially anonymised).

For evidence material to be acceptable, it is essential that these make mention of: [1] the trademark; [2] the goods sold under the trademark; [3] the geographic location; as well as [4] an indication on the time of use.

Advertisement and sale actions in a determined country or jurisdiction are generally realised through the intermediary that imports/distributes the Studor products. Therefore, evidence of use consequently resides to a large extent in their hands.

In view of being able to address possible challenges in the future, it is highly recommended to keep an archive of evidence material for each of the Studor trademarks, over a period covering the last five years.

Throughout our history, we have worked hard to ensure that Studor is a name associated with high quality and reliable products – this obviously being of utmost importance when we consider the importance of protecting the trap seals in the drainage system. Consequently, Studor has a zero tolerance policy in relation to patent and trademark infringements and will take any appropriate action.

Studor – over 40 years of expertise, a lifetime of quality!

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World Plumbing Day 2017

march 11, every year… everywhere

Plumbing – Vital to Global Health
Because Every Day is World Plumbing Day

Yes, another year has gone by since the last World Plumbing Day (WPD), and here we are again with the opportunity to “reaffirm our oath to use our collective expertise to safeguard the health of our communities” and to “promote the important role played by the industry“.

To this end, Studor continues to play a key role in educating the industry on the importance of water trap seals for human health – one of the four key elements with which plumbing is associated. Our most recent activity in this area being our “Seeing is Believing” test tower, which demonstrates that not only is the Studor System more than capable of protecting the water trap seals, but also that it out-performs the convention vent pipe system.

One of the other key elements is “water” – a valuable and finite resource that most of us take for granted. It with consideration to this aspect that Studor continues to support the work of  the charity DROP4DROP and would like to share their latest update (a big thank you to the DROP4DROP team!):

In many parts of the world, access to safe, clean drinking water is scarce. 663 million people do not have access to this basic human right. The lack of access to clean water and safe sanitation not only threatens the health of individuals, but impedes social and economic development on a global scale. DROP4DROP works across the globe to provide sustainable sources of clean drinking water to those currently living without.

DROP4DROP is currently working within communities across India and Africa. With research continually undertaken to ensure the most effective technologies are used, DROP4DROP strives to ensure communities have access to a sustainable source of water clean drinking water.

By employing local labourers and involving the community throughout the project process, a sense of pride and ownership is established with every constructed bore-well. Providing maintenance and hygiene education ensures maximum longevity of the well and promotes a positive attitude to hygiene and health.

Thanks to the generosity of Studor, work can continue to provide clean water to those currently living without access. This month DROP4DROP is collaborating with VOX United to deliver a large-scale bore-well restoration scheme across Mozambique. Mozambique has one of the lowest rates of water and sanitation coverage in Sub-Saharan Africa and has the 22nd highest rate of child mortality worldwide (World Health Organization). The country also struggles with floods and earthquakes, which dramatically affects communities’ abilities to collect water. Poverty levels are high; 49% of Mozambicans do not have access to a clean water supply and this figure rises to 62% among the most rural communities. Many Mozambicans rely on collecting water from natural sources such as lakes and dams. Subsequently, the risk suffering from waterborne disease is incredibly high.

As women and children face the responsibility of collecting water for their families, alleviating the time spent travelling to the nearest source ensures children can focus on their education, and women can enter paid employment. By providing Mozambican communities with a functioning bore-well will not only improve the health of the community, but further aid the economic and social development of Mozambique as a country. Alongside the restoration of broken bore-wells, selected members of each community are trained in maintenance and encouraged to monitor the use and productivity of the well, ensuring repairs can continue without DROP4DROP present, securing longevity and success of each community bore-well.  

Links to previous Studor articles on World Plumbing Day:

World Plumbing Day 2016

World Plumbing Day 2015

World Plumbing Day 2014


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Rock and roll at Studor’s “Seeing is Believing” test tower

Tony Hill at the base of the test tower

Tony Hill (our Technical Sales Engineer) shares with us his slightly hairy most recent experience at our “seeing is believing” test rig in the UK’s National Lift Tower:


The test tower on a calm day!

If you’re hoping to read about The Rolling Stones or The Who then I’m sorry but I’m going to disappoint you – instead I am talking about when “Mother Nature” flexed her muscles (and the tower!) with a show of strength and force by way of “Storm Doris” on Thursday 23 February 2017.

We had a “Seeing is Believing” demonstration booked for the afternoon, despite a few people having cancelled the day before (maybe they heard about the predicted winds!), but in true Studor fashion we decided that “the show must go on”! Around lunch time we could feel the tower rocking and rolling in beat with the wind, and decided that as we had a few minutes to spare before our guests arrived that we’d travel to the very top of the tower.

The journey in the lift should have prepared us with a few side scrapes on the way up in the lift car, but when the doors opened at the top… WOW! Never before in the 2 years I have been at the tower had I ever felt the experience of such a sway! Ed Wright, the National Lift Tower Manager, had an app on his phone which measured the sway at about 2 degrees from centre. We quickly decided being that high and starting to feel land sick from the swaying motion that it was a good idea to get down lower!

What exactly is 2 degrees at that height? Well, thanks to Phil Henry of Polypipe Terrain obviously paying attention to trigonometry classes at school, and the rest of us trying to look clever with the aid of a little friend called Google(!), the calculations were done – we worked out that the top of the tower was moving about 75mm off centre with each gust of wind.

Needless to say, the show went on regardless, and the Studor System once again proved to outperform the standard vented drainage system built to the code in every way, but for the next 24 hours I could still feel the sway in my legs!

I’m sincerely hoping that “Storm Ewan” stays well clear of the tower whilst I’m up there this week…

Posted in Meet the team, Seeing is Believing Test Tower | 1 Comment

From novice to drainage ventilation specialist: Michael Chang

In this blog we bring you something a little bit more personal from our Product Engineer, Michael Chang, who has been a member of the Studor team for over 12 years:

I was a vehicle apprentice technician in Hong Kong before I came to the UK to study for a BEng Mechanical Engineering degree. I knew nothing about plumbing before I joined Studor and it was a big challenge to start with, but I soon developed a sound knowledge base and after a few years I completed an Engineering Design Master’s degree based on Studor’s development projects.

My inquisitive nature and drive for personal development has enabled me to develop an in-depth specialist knowledge of plumbing ventilation. I continue to see plumbing technology as an interesting subject – particularly as it is “behind the scene” but no building would function without it. There are still a lot of people who don’t know why there is a water trap in every fixture unit, although it is a relatively straight forward and simple principle – there is still a lot of education work to do!

Being an engineer, I am always interested in how things work and trying to figure out how things could be improved. I recently took the opportunity to visit the Science Museum in London. What an experience! It was like travelling back in time, and even has one section about the development of toilets (“water closets” (WCs)).


Cummings’ water closet patented in 1775 (source: see below)

If we go back in time, the “big bang” of plumbing was in the late 15th century: It is quite amazing to consider that since the first WC was invented in 1596 by Sir John Harington for Queen Elizabeth (and later reinvented and patented in 1775 by Alexander Cummings) that the principle is still the same! More about “Toilets, earth closets, and house plumbing” can be read on the site dedicated to The History of Sanitary Sewers.

The drainage system is an essential part of the “digestive system” of the living space in houses and buildings; the behind-the-scenes aspect that most people, including myself before I joined the Studor team 12 years ago, would even think about. It is amazing how something given so little thought is so important!

Quite simply, the water trap is a barrier of water which separates waste water and air from the living space. However, the air pressure on both sides of this water barrier must be balanced – both positively and negatively. You can read more about this in our “The Only Line of Defence” blog.

I find it really rewarding working for a company which is positively contributing towards a healthier living environment for everyone!  It is challenging environment – always trying to figure out how to save time, space, cost, and solve difficulties. Sometimes I find that it is best not need to think too much otherwise it would become complicated – I do believe that “less is more” and “simple is the best”!

Cummings’ water closet image sourced from

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Why the CE Mark alone is not enough…

Studor has remained a pioneer of standards and approvals for drainage ventilation products since being founded in 1975. When European Standard EN12380 was introduced for Air Admittance Valves (AAVs) in drainage systems in 2002, it was natural for Studor to not only to comply with the standard but to take that step further and seek independent validation of conformity. This was achieved by the issue of the DIN CERTCO KEYMARK in 2005 for the Mini-Vent and Maxi-Vent. Studor now holds several KEYMARK certificates across the range of AAV products.

Sören Scholz, Head of Certification Body for “DIN CERTCO Gesellschaft für Konformitätsbewertung mbH”, has kindly taken some time out of his busy schedule to talk to us about DIN CERTCO and the KEYMARK scheme:


Who is DIN CERTCO and what do they do?

DIN CERTCO is the certification organisation of TÜV Rheinland and DIN, the German Institute for Standardization, highly regarded internationally for its independence, neutrality, competence and extensive experience in the certification of products, services, qualified enterprises and persons. DIN, as other standards bodies, maintains a comprehensive collection of technical rules that sustain the efficient manufacture, testing, and assessment of products. DIN promotes the application of standards by its activities in the field of conformity assessment. Testing and assessment can take various forms: from the supplier’s declaration of conformity to third-party assessment, from proto-type-testing to type examination, or the assessment of a quality or environmental management system. With its network of partners, DIN CERTCO offers certification services that adapt flexibly to specific requirements. As a result, the proof of conformity provided exactly matches the scope deemed necessary.  Since 2015, the empowerment of certification bodies, the administration of the KEYMARK, and the management on behalf of CEN is assumed by DIN CERTCO as the KEYMARK Management Organization (KMO).

What is your role in DIN CERTCO?

I am the Head of Certification Body at DIN CERTCO. We were anxious to extend the certification business at DIN CERTCO in the area of heating and air-conditioning products, although for these kinds of products the certification has a long tradition in Germany. Together with the interested parties we develop specific certification schemes and implement them in addition to the relevant standard(s). Our DIN certifications help specialist planners, installers, builder/owners in the public and private sectors in the decision-making process. We think that the voluntary product certification becomes more and more important, especially for the growing European market. Therefore a quality mark well known Europe-wide is very important for both, manufacturers/suppliers and consumers.

What is the KEYMARK?

On recommendation of the European Council to improve consumer protection and to counteract the uncertainty of consumers by a mark variety, the European Standards Organisations CEN and CENELEC developed the harmonised European Mark System for standardised products. The KEYMARK is the European quality mark showing the conformity of products with European Standards. A product may only be marked with the KEYMARK if it has been tested and certified before by a neutral, independent and competent body. The factory inspection and Initial Type Testing (ITT), together with regular inspection, constitute an important element of the procedure for granting the KEYMARK. Beyond that, the manufacturer has to carry out a Factory Production Control (FPC) in consideration of the relevant product standards and the elements of EN ISO 9001. This quality system is controlled by an annual inspection and is completed by type testing which takes place at least every 2 years. Today, there are many products using the KEYMARK as a European quality mark, including:

  • Clay pipes
  • Heat pumps
  • Solar thermal products
  • Thermal insulation products for buildings and industrial applications
  • Thermostatic radiator valves
  • … to name just a few!

What is “DIN-Geprüft”?

To improve the confidence in the KEYMARK, it is often granted in combination with marks of existing national certification systems which are based on the conformity with European Standards. In Germany, the KEYMARK is often granted together with the well known Certification Mark “DIN Geprüft” (= DIN Tested). The KEYMARK symbol and “DIN Geprüft” together form the KEYMARK certification.

What’s wrong with just using the CE mark?

The CE mark is basically a self-declaration. There are strict requirements a manufacturer must comply with in order to apply the CE mark, but in most cases, there is no requirement for independent validation that these requirements have been met. The CE mark shows the observance of legal minimum requirements, but the KEYMARK provides a real surplus value for the consumer: tested and certified observance of uniform European Quality Standards.

How does the KEYMARK affect the STUDOR products?

Several of the the Studor Air Admittance Valves have been issued the KEYMARK certificate, which certifies that they conform with the requirements for CE marking as laid out in European Standard EN12380.

Are any other Air Admittance Valves certified with the KEYMARK?

At this time, STUDOR and Geberit are the only manufacturers to be issued with the KEYMARK certificates.

Where can I find more information about DIN CERTCO and the KEYMARK certification?

DIN CERTCO’s website provides detailed information in German and English at

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