Partnering with excellence…

One of the things that our experience as world market leader in drainage ventilation has taught us is that it very difficult to make a top quality Air Admittance Valve. Membranes have to be extremely correct; they must be exactly seated, as the slightest warp will make the valve leak – with such marginal tolerances in the valve, precision in the manufacturing process is key. It is therefore critical that we are highly selective in the manufacturers we work with. One of our manufacturers, based in the USA, is Dymotek, Inc., who kindly shares some words with us about the company:

Dymotek, Inc., is a leading plastics manufacturing company in the Northeast United States. Our vision is to provide world class customer experiences by providing consistent, value added, dynamic thermoplastic and liquid silicone rubber (LSR) solutions. We were recently recognized as “Processor of the Year for 2016” in the United States.

As a full service provider we have molded component manufacturing, value added services such as pad printing and assembly, and multinational order fulfillment of project-specific bulk packed or retail packaged Air Admittance Valves (AAV) direct to Studor’s customers and distributors.

In our manufacturing environment, there are a few factors that have direct influence over pricing:

  • raw materials (resins/ silicones)
  •  overhead
  •  labor

RAW MATERIALS/PACKAGING: Commodity resins used for the majority of injection molded products are commercially available and tend to follow standard market pricing. Engineering resins are more complicated dependent on the product’s unique requirements and don’t typically fluctuate directly with the market. With a proven history of volume and continued efforts by Studor to grow the AAV market, Dymotek is able to foster competitive rates with suppliers and negotiate inventory levels, terms and delivery for mutual benefit. These same principles are applied to retail packaging such as individual boxes and installation instructions. We take pride in our close relationships with local suppliers that offer not only quality made packaging and stored inventory, but world class customer service, available same day delivery and creative solutions for cost reduction to share downstream.

OVERHEAD: Dymotek endeavors to provide value. Integrated quality checks performed by automation, regular dimensional and visual inspections performed by skilled personnel during several stages of the manufacturing process, and leading technology designed into equipment ensures that every assembly is validated before packaging.  Dymotek, as a supplier of highly regulated products offered both domestic and international requirements is audited a minimum of 17 times annually. The majority of audits being unannounced. Our Quality Management System (QMS) is registered to ISO9000:2008 (soon to be ISO9001:2015 in early 2018) with regular audits to ensure continued compliance and commitment to systemic improvement.

LABOR: We have a highly automated manufacturing facility that reduces the impact of costs and quality for labor. Every stage of manufacturing for all products at Dymotek is well defined, regularly monitored, and diligently documented. We say what we do, do what we say, and welcome review by our customers and certification bodies. Our systems are regularly reviewed internally by trained auditors who seek to identify areas for improvement. We have won multiple awards in our industry for employee satisfaction.

It is a source of pride for all associates from senior management to the core of the business, our machine operators and technicians, to not only see an opportunity to make an improvement, but also receive the resources and encouragement to put their ideas into practice.

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International Women in Engineering Day: Christa Wang



Christa Wang, Sales Manager for Studor’s Taiwanese distributor Metropole, has now been working with Studor for over 14 years. She leads an all-male engineering team, promoting the Studor System in Taiwan as a key part of her role.

So far her team has secured more than 1,200 projects of complete Studor AAV drainage systems in Taiwan; varying from hotels, commercial buildings, and high rise residential buildings through to hospitals and facilities. She is driven by the achievement of winning more projects and seeing the growth of sales targets each year.

Engineering Speciality:

Water Supply & Drainage System, Electrical System



What got you interested in engineering?

I found that the variety of engineering appealed to me. By integrating marketing and technical engineering knowledge, I enjoy the challenges of making our customers easily know our new technology, good products, excellent systems and all of the different types of projects involved.

Where did you study:

Mainly in Taiwan, but also for two years in Freiburg, Germany.

What’s the most notable project you’ve ever been involved with and why?

The most notable project that I’ve been involved with was promoting the reform in the Taiwanese National Building Code for the design of building water supply and drainage systems.

The tallest project I’ve been involved with is the Mega Tower, a 50-floor commercial building owned by Far Eastern Retail Group, located in Banqiao, New Taipei city.

What specific skills or attributes do you feel that women bring to engineering?

Most women are more detail-orientated, more attentive and more thoughtful than men. These features help me doing well in managing each projects and customers’ needs.

Women constitute a small percentage of engineers versus men. What advice or thoughts can you give to women thinking of studying or training to become engineers?
  1. Always be confident and strong-minded. Always have courage and executive power. Always persist in right things. Keep these in your mind, and you will succeed in the end.
  2. If you want to success in the field of engineering, just persist in doing what you think is right until seeing opportunities; instead of insisting in something while seeing opportunities.
  3. I believe that my fate is in my own hands not in others’ words.
  4. Discover the best of you.
What do you enjoy doing outside work?

I enjoy reading, exercising and traveling in my personal time.

I have climbed 5 high mountains to the altitude of 3,000 metres or even higher!

I have translated a series of children’s books from German into Traditional Chinese. I found that this was a really fun process.

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International Women in Engineering Day: Nicola Schofield




Our interview today is with Nicola Schofield, Building Energy Modelling Senior Consultant for BRE in the UK, who works alongside the Principal Engineer responsible for testing the Studor products.

Engineering Speciality:

Building Physics, Energy Efficiency



What got you interested in engineering?

I first studied theoretical physics and found it a little too abstract and unrelated to the everyday world. I then studied architecture, but found it a little too lacking in mathematics and science! I’ve always had an interest in the environment and green technology so building science and energy efficiency was a perfect mid-point for me.

Where did you study:

The University of York (MPhys in Physics) and Leeds Metropolitan University (BA in Architecture), which was renamed in 2014 as the Leeds Beckett University.

Any other personal details you feel would be of interest to readers:

I work on developing energy efficiency methodologies and tools for the built environment to be used on a country-wide scale through to bespoke dynamic modelling of individual buildings to investigate issues such as overheating.

What’s the most notable project you’ve ever been involved with and why?

SAP, which is the calculation methodology most likely to be recognised as it underpins the Energy Performance Certificates (EPCs) needed when renting or selling a house in the UK.

What specific skills or attributes do you feel that women bring to engineering?

I like to know how things work and why. I like to solve problems and build things. I think rather than there being particular attributes that women should/could bring to engineering, a group of people with different backgrounds, experiences and viewpoints is best to creatively problem solve any engineering task. This means a multidisciplinary group of women and men with open minds to exploring new ideas.

Women constitute a small percentage of engineers versus men. What advice or thoughts can you give to women thinking of studying or training to become engineers?

Engineering is not limited to the few specific stereotypes that are often portrayed in films and TV. Instead, it is a high-level term that encompasses a wide variety of careers. If you enjoy designing and creating or applying any sort of knowledge to build things in the real world then there is probably an area of engineering that you would both enjoy and excel at.

What do you enjoy doing outside work?

I enjoy urban sketching, painting, dressmaking and anything creative.

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International Women in Engineering Day: Maribel Adia-Lim



Today we meet Maribel Adia-Lim – Principal Public Health Engineer from ARCADIS Design & Consulting (formerly Hyder Consulting). She manages to balance a successful career with a busy home life and still find time for hobbies and charity work!

Engineering Speciality:

Public Health



What got you interested in engineering?

Since high school I always wanted to become in engineer.

Where did you study:

I completed my first BS in Civil Engineering at Adamson University (Philippines) in 1989 and my second BS in Sanitary Engineering at National University (Philippines) in 1997.

Any other personal details you feel would be of interest to readers:

Being an engineering professional and a mother of two boys is a very tough job – I always need to manage my time to become a good mother and a good leader in our team.

My hobbies are cooking and gardening. I enjoy cooking so much because I feel happy whenever I am successfully creating different masterpiece recipes/dishes for my family. I am also fond of sharing my dishes with my office mates so that they can comment on my dish and make some improvements if there are any negative remarks.

Gardening, on the other hand, makes me feel cheerful  because it relaxes my mind whenever I see my plants everyday. Most of the time, I give some of plants to my office mates and I encourage them to take good care of them. I keep on telling them that plants can relax minds whenever stress is around.

Whilst I’m based in the Philippines, I can actually be involved with projects just about anywhere. To quote from our ARCADIS website: “[We] work collaboratively to create value through built and natural assets that work in harmony with their surroundings – from shopping centers in Shanghai to new rail systems in Doha and reducing air pollution in Los Angeles. Arcadis. Improving quality of life.” I love the variety that this offers!

What’s the most notable project you’ve ever been involved with and why?

There are a couple of notable projects I’ve been involved with:

  • Pentominium Tower in Dubai, UAE (which has the Studor System installed in it) – construction is currently suspended, but it will be the tallest all-residential building in the world upon completion (122 storeys above ground).
  • Security Forces Medical Center (SFMC) in Riyadh and Jeddah, Kingdom of Saudi Arabai – this will be the largest hospital in the world (design still ongoing).
Have you been involved in any projects where the Studor System has been installed? 

Yes – I’ve worked on several projects in Dubai, UAE where the Studor System has been installed:

  • Palazzo Versace – 10-storey luxury hotel and residential condominium
  • D1 Tower – 80-storey residential tower
  • Pentominium Tower – 122-storey Residential Tower
  • Plot 38/Tower 38 – 60 storey residential tower
What specific skills or attributes do you feel that women bring to engineering?

Solving problems through engineering solutions is what we can contribute to our profession. Thinking as an engineer to solve a problem is quite different in a solution of an ordinary person. As a woman, hard work, patience and creativeness is already there. Being diplomatic and more emphatic are some of the tools that I might say are useful in collaborative projects.

Women constitute a small percentage of engineers versus men. What advice or thoughts can you give to women thinking of studying or training to become engineers?

Women are capable of becoming engineers just as much as men do. By doing training, some researche and through life long experiences, women can give a big contribution to the engineering profession. All I can say is that through hard work, perseverance, and eagerness to learn, we will all succeed!

What do you enjoy doing outside work?

I enjoy doing charity work which is sponsored by the company together with the Philippine Red Cross.

Since 2011 I have also been a volunteer for the APFI foundation for children and have participated in several volunteer projects which are primarily for the less fortunate. During the summer we teach out of school youths for them to become scholars of the foundation. Aside from that, I am also actively participating in medical missions and food feeding programs. Alongside my work and home life, I find it really rewarding to be giving something back to society!

I also really enjoy costume making, concept contribution and prop preparation for the Christmas Party. One of the funniest things I’ve ever done was to join the dance group for our Christmas Party presentation – what I lacked in skill I certainly made up for with enthusiasm!


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International Women in Engineering Day Focus: Tanya Ibrahim



Today we’d like to thank Tanya Ibrahim, Engineer for Plastics, Pipes, and Fittings Department at NSF International, Ann Arbor, Michigan, USA, for sharing a bit about herself with us:

Engineering Speciality:

Majored in Chemical Engineering



What got you interested in engineering?

I was really interested in chemistry and mathematics in highschool, and that drove me to pursue an engineering degree. In addition, my dad is a Civil Engineer. Seeing his drive and dedication really made me want to follow into his footsteps and pursue the Engineering field.

Where did you study:

I completed my BS in Chemical Engineering from Wayne State University in 2015. I was also the first student from WSU to graduate with a certificate in Nano-engineering. I currently attend the University of Michigan in pursuit of my MS in Engineering Management, estimated to be completed by December 2017.

Any other personal details you feel would be of interest to readers:

As first generation Lebanese, I am bilingual in English and Lebanese. I used to work for an automotive supplier as a Quality Engineer. When I graduated I did so “Cum Laude”, having researched improving the combustion properties of petroleum coke for DTE Energy.

What’s the most notable project you’ve ever been involved with and why?

I managed a project that involved the certification of a world-leading provider of power tools. The project involved overseeing and scheduling all testing for compatibility of pipes and fittings joined together with the power tool. This project spanned over 7 months.

What specific skills or attributes do you feel that women bring to engineering?

I believe that women are really detail-oriented, driven, and natural leaders. Working as a woman engineer in a male-dominated industry shows that we are tough and we don’t mess around. Women think critically and that’s one of their best attributes that they can bring to this challenging field.

Women constitute a small percentage of engineers versus men. What advice or thoughts can you give to women thinking of studying or training to become engineers?

Engineering is an industry that can open so many doors for you. It’s a versatile career path. You can do anything from work in automotive, cosmetology, plastics, architecture, etc. No matter how tough it gets, stick it out. Engineering is the most rewarding career path, because you will make a difference in society, so stick it out!

What do you enjoy doing outside work?

Outside of work I enjoy working out, travelling, and spending time with family and friends.

Any other information or comments?

I really hope that more women are inspired to pursue engineering as a career choice. Although I was 1 of 3 females in my 2015 graduating class, I don’t feel like there are any barriers for women in this field. Women need to not avoid the career because engineering is labelled as a “man’s job”. We need more women in the field and I hope any women reading this think hard about engineering as an option before picking a career path.

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International Women in Engineering Day: Friday 23 June 2017

INWED - 23 JuneInternational Women in Engineering Day (#INWED2017) was initially launched in 2014 as the UK’s “National Women in Engineering Day” by the Women’s Engineering Society (WES) to celebrate their 95th anniversary. Each year it has gained more momentum, and has now evolved into a truly international day of recognition of the contribution that women have to offer engineering. Last year it was even given UNESCO (United Nations Educational, Scientific & Cultural Organization) patronage!

This Press Release from WES provides a good overview of INWED which takes place on Friday:

Women make up less than 10% of the engineering sector in the UK. With a large skills gap looming and the additional need for a more diverse workforce, it has never been more important to inspire and encourage more people, especially women, to choose a career in engineering.

Set up in 2014 by WES to celebrate its 95th birthday, this national, and now international, awareness day focuses attention on the amazing career opportunities in engineering and technical roles, including for girls and young women, and celebrates the achievements of women engineers and technologists.

Working in partnership with many of the engineering world’s globally recognised names, WES itself will be celebrating the day with events in London. UK-based engineering and innovation company Colas Ltd, one of the sponsors of INWED in 2017, has worked with WES to hold a Breakfast Roundtable at the House of Commons, hosted by Mims Davies, MP for Eastleigh. Participants will include Allan Cook (Chair, Atkins), Benita Mehra (WES President) and Caroline Gumble (Chief Operating Officer, EEF).

This invitation-only panel will seek to explore key ways forward in an international context and highlight issues related to women in engineering. It will explore one of INWED’s key themes in 2017, ‘men as allies’, for, as Caroline Gumble explains: “Without male decision makers as allies, women will continue to be unrepresented in the engineering sector at all levels.”

Lee Rushbrooke, CEO, Colas Ltd, commented: “Colas is a proud sponsor of International Women in Engineering Day 2017, promoting, rewarding careers and opportunities in engineering for women. Colas is committed to supporting greater diversity within the sector and actively encourages women in engineering.”

Benita Mehra, President of WES, remarked: “WES exists to provide a voice to women in engineering. We need to find more and better ways to increase the number of women taking a full part in engineering and allied sectors with actions from employers, educators and policymakers. I am very much looking forward to sharing this INWED Roundtable with such eminent and influential colleagues.”

Studor recognises the contributions that engineers of any gender have to offer the industry. However, it is a documented fact that women constitute a small percentage of engineers versus men. In support of #NWED2017, each day this week we will again be publishing a short interview with a variety of international female engineers.

Tanya Ibrahim

Tanya Ibrahim
Engineer for Plastics, Pipes & Fittings

Maribel Adia-Lim - Principal Public Health Engineer

Maribel Adia-Lim
Principal Public Health Engineer

Nicola Schofield - Building Energy Modelling Senior Consultant

Nicola Schofield
Building Energy Modelling Senior Consultant

Christa Wang - Sales Manager

Christ Wang
Sales Manager


More information on INWED and WES can be found on the respective websites.


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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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