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[...]The regular inspection of installations is an important aspect not to be underestimated where drinking water and wastewater structures need to be maintained as valuable elements of our supply and disposal networks. Regular inspections are the only way to ensure the plants and their peripherals can safely be operated a long time. It is of fundamental importance to early identify defects, damage and weak points by regular inspection so that these can be expertly eliminated as soon as possible. The risks of continuing with run-down equipment are not to be neglected, especially not in the field of drinking water supply! In practice, there are various reasons why it may become necessary to refurbish equipment: The installation is already damaged and represents a risk for its functional reliability. The installation represents a safety risk for life and health. There is the risk that a defect may develop into a damage, The drinking water is or could be adversely affected. The required effluent quality of the wastewater treatment plant cannot be met anymore. The reliable and trouble-free operation cannot be guaranteed anymore. Operation and maintenance costs are too high. Unauthorized persons could wilfully cause damage if equipment is old and worn down. The plant or structure does not meet anymore the legal and/or technical requirements. There are different options of long-lasting, reasonable refurbishments for different specific requirements. A lot can often be achieved already with simple measures! Special products and plants made of stainless steel offer the optimal conditions for a safe and reliable function over a long time, provided they are processed and installed professionally. For many years, the products and techniques offered by HUBER SE have well proven their efficiency in many different environmental applications. Plant operators can profit in the long term, both in technical and economic terms.[...]

[...]In Germany, Austria and Switzerland, enough water of high quality is naturally available at any time. One could almost forget that our most important resource is highly sensitive and gives life not only to humans and animals but also to germs and microorganisms. There are therefore good reasons to protect our water resources and use air filters in drinking water reservoirs. “We have never always built water reservoirs without air filters. Why should we use air filters now?” You may have heard this provocative counter-question sometimes from a customer when you recommended that he should improve his reservoir and try something new. If you sometimes do not have the time and patience or the right arguments in such a case to counter such a question, frequently asked by a person with “experience”, we explain in the following several good reasons why to use air filters in water reservoirs: Water comes clean from a spring or well and is intermediately stored in a "clean" reservoir before it is distributed to the consumers via pipelines. Even if the operators of public water supply facilities are well familiar with germ numbers, they often do not consider that the source of germs can be dust in the air which the water reservoir sucks and releases. The long established practice of using ventilation chimneys in water reservoirs is still very common, frequently with “diagonal” supply and exhaust air streams. Many operators think it is enough to have an insect screen with 1 mm mesh or perforation. They think everything is all right with some air draft. Basically, air exchange is the right idea but only as long as the air is very clean. We all tend to forget that dust is always present in the air. We only remember it in spring, during the blossoming of the trees, when a yellow dust layer covers our cars we have cleaned the day before, or once a year when the wind brings dust from Africa and colours the sky in ochre creating exceptionally beautiful red sunsets. We should then be aware that also our water reservoirs ‘breath in’ this dust and the undesired germs contained if the air remains unfiltered. We want to explain below how much dust and germs are present in the ambient air which stream into the water reservoir with the unfiltered air and settle on the water surface and the reservoir walls and ceiling. Due to their huge volume water reservoirs are ideal ‘dust settlement chambers’ where the air is cleaned like in a wet scrubber. But the problem is that the scrubbing water is our drinking water. We should therefore think twice and better filter the air before we say: “We have never used air filters. Why do we need them now?” The HUBER catalogue "Innovative Solutions for Potable Water" and our PG8 brochure “Hygiene in Drinking Water Reservoirs” explain the fundamentals of air filtering for water reservoirs. An annual amount of 21,000 mg dust and 1680 billion germs pass into a 500 m³ water reservoir. This figures can be explained: If you search the internet to find the 'average dust content', you will find 0.05 mg/m³ (after rain events) or 0.1 mg/m³ (dry weather) in rural areas and 0.1 to 0.45 mg/m³ in urban areas (source: ikz.de). This is not much, one may think at first glance. But we should look at these figures in more detail: If we assume a ventilation number of only 1.2 per day, due to the varying water level, and multiply it with the a.m. 0.1. mg/m³ and 365 days, the result is 500*1.2*0.1*365 = 21,900 mg or 21.9 g per year, which is not a small amount. We offer our HUBER air filter plants L251, L252, L361 and L661 especially for the use in water supply facilities. Air throughput capacity is specified for a pressure difference of 120 pascal. In order to dimension the filter plant to suit the individual water reservoir, we use the formula “reservoir volume divided by 2.0 to 2.5”. The water reservoir either breathes the air in and out automatically as the water level falls and increases, or an additional ventilator is installed upstream of the filter (and operated with overpressure!). An additional ventilator is recommended where condensation is expected to occur and needs to be reduced. In this case, it must also be provided for an outlet air duct with a flap closing without current. For applications with an additional ventilator we recommend to use the type L 361 filter plant if there is sufficient space. Our L 361 filter plants have a class F6 fine filter upstream of the class H13 filter for suspended matter. The fine filter retains already approximately 95% to 99% of the dust (depending on particle sizes), with the result of a significantly longer life of the class H13 filter with a gravimetric separation efficiency of 99.95%. H13 filters are used in clean rooms, semiconductor production, sterile bottling plants of the pharmaceutical industry, or to filter the exhaust air from nuclear-technical plants. The costs of a HUBER air filter plant are in the parts per thousand range of a complete new building project or complete refurbishment of a water reservoir. The budget for an air filter plant without pipelines and additional ventilator is 1,500 to 3,000 €, depending on the range of equipment features. No chimneys are required if a lateral safety louvre with insect screen and wall connection plate is used.[...]

[...]Coarse screens are the protective equipment of a screening system. Their task is not removing the incoming screenings from the water flow, but coarse screens are used to protect downstream finer screening systems (or machine technology in general) in the event that massive amounts of coarse material or extreme-size debris occur. Such unusual events in the operation of a screen include the occurrence of large-volume flotsam (e.g. tree trunks, tyres, etc.), man-sized screenings rolls, suddenly occurring huge quantities of screenings or large debris and sediment loads at the channel bottom. Such disturbing material can - provided that no coarse screen is available - severely impair or interrupt the operation of screening systems and also lead to damage to the respective machines. The art is to select the right coarse screen for the application in question so that the screen reliably detects and removes the impurities from the channel during operation. With the HUBER Multi-Rake Bar Screen RakeMax ® and the HUBER Coarse Screen TrashMax ® , HUBER has two screening systems on the market that cover most of the requirements of common coarse screen systems. But what to do if there are applications and/or channel and structure dimensions where these machines reach their limits? The answer to this question is the new HUBER Grab Screen TrashLift, whose functional principle is really simple: A solid stainless steel shell acts as an "excavator bucket" to clean the channel bottom as well as the bar rack section. This excavator bucket is operated cyclically by a winch system. With this functional principle it is possible to realize channel widths up to 6 m and channel depths up to 40 m with a 90° installation. In order to ensure maximum operational safety and service life of the machine, the HUBER Grab Screen TrashLift is characterised by the following features: Detection of blockages of the bucket carriage in the up and down movement (overload and slack rope detection of the load winches) Long rope service life due to directly acting load ropes / control rope on the bucket and winch drum, no unnecessary rope deflections Safe transport of the flotsam and screenings, even in 90° position, thanks to the active bucket closing mechanism Safe flotsam/screenings discharge through a scraper and swivel mechanism of the bucket at the discharge point[...]

[...]An innovative building block for your digitisation strategy The main duty of the screens installed in the inlet to sewage treatment plants is to protect downstream machines and systems and ensure perfect operation of the sewage treatment plant. When selecting the headworks screens it is usually assumed that coarse material up to a certain maximum size will occur. Increasingly, however, unforeseen material such as cans, wood pallets, large tree branches or even iron rods are also found in sewers. Although such coarse material should definitely not be present in a sewer, there is no possibility to reliably exclude they are there. If such material arrives at a screen and the screen takes it up, this may result in mechanical damage of the screen or downstream systems, such as conveyors, wash presses, etc., and this can lead to severe failures in the operation of a sewage treatment plant. The innovative system HUBER Safety Vision is able to identify critical coarse material and protect machines safely and reliably against damage. Optical sensors continuously monitor the shape and size of the coarse material taken up by the screen. The sensor data are evaluated in real time through digital image processing. Whenever the system detects any impermissible material, a warning message with image is immediately sent to the operating staff. They can decide if the screen is to continue running or stop until the material has been removed. This process reliably prevents blockage or damage of the screen or downstream systems and at the same time increases equipment availability. Another advantage of the HUBER Safety Vision is the preventive identification of explosion risks. Accidents or failures may lead to the ingress or unpermitted feeding of inflammable liquids and gases which can cause an explosive atmosphere in the inlet to a sewage plant even if only small amounts are present in the sewer network. Knowing the explosion risks is essential for the operating reliability of the plants but especially for the health and safety of the operating staff. To ensure reliable monitoring, a sturdy scalable gas alarm device is installed directly on the machine which can trigger an alarm in real time whenever pre-defined limit values are exceeded. HUBER Safety Vision provides the technological preconditions for a variety of applications: Intelligent detection of impurities Continuous monitoring and identification of abnormalities Intelligent preview and early detection of disturbances Continuous transmission of live images Exact determination of the volume and dimensions of screenings by a 3-D scanner and load-dependent control of downstream systems Reduced machine run times Load-dependent adjustment of maintenance intervals Predictive maintenance Reduced maintenance and repair costs Immediate signal from the image processing software to the machine control system if limits are exceeded Detection of explosion risks before they can become dangerous Integration of smart phones, tablet PCs and mobile or stationary displays of a PLC. Due to the variety of possibilities the system provides, HUBER Safety Vision represents an important element in the digitalisation strategy of any sewage treatment plant. Especially the pollution load-dependent control of systems installed downstream of the screen provides a considerable cost saving potential as it reduces unnecessary operation hours and consequential expenses for maintenance and repairs and increases the lifetime of the systems. The impurity detection system HUBER Safety Vision it is possible to identify critical coarse material and protect machines reliably against damage. If the screen is stopped by an obstacle, it is labour-intensive to remove it. At least two persons with suitable tools are necessary to put the screen into operation again. Frequently, they additionally have to repair damage. Warning messages and live pictures can be sent to the staff and varoius devices[...]

[...]Stay on the safe side! The need for security has strongly increased especially in the recent past. This development can be recognized in nearly all situations of life. The security requirements are however especially high where a great many people could be affected very easily. Drinking water supply is an example for such a case. The facilities in this sensitive environment are often in a very poor condition. To identify potential weak points, the authorities recently simulated burglary attempts on public institutions, among them also drinking water supply structures. This campaign lead to a significant increase in inquiries we received for attack-proof products for improved security. There are, however, a variety of other structures in sensitive areas that have inspection openings and entrances and therefore need also special protection against unauthorised access. The specifications of DIN EN 1627 define resistance classes, resistance times (the period for which a product can withstand a burglary attempt), type of criminal, and the so-called ‘modus operandi’, i.e. how the offender proceeds. According to DIN EN 1627, six different resistance classes are defined for burglar resistance, with RC 6 as the highest class (RC = resistance class). Which resistance class is required for which application depends on the individual hazard situation (risk), e.g. where the object is located and how easily the hazard area can be observed and overlooked. The advisory bodies of the State Offices of Criminal Investigation recommend for example resistance class RC3 for entrance doors to water supply installations with burglar alarm system. If there is no burglar alarm system, it is recommended to use security doors that offer resistance class RC4. Security doors certified to resistance class RC3 and RC4 have been in the product portfolio of HUBER SE for several decades already. To increase also the safety factor of manhole covers, our program includes now manholes covers certified to resistance class RC3 according to DIN EN 1627. The term “burglar-resistant” thus is clearly defined also for manhole covers and represents comparable values according to the latest security definitions. Some details were optimised as a result of the security test. The lock for example is now a lock system with anti-drilling protection. Also manhole covers can be equipped with a magnetic contact as OPEN/SHUT indicator. We have many years of experience in the manufacture of manhole covers of all kind and have therefore placed the focus on maximum resistance to unauthorized entry into the shaft when developing and manufacturing burglar-resistant manhole covers. Let us find the weak points of your plant before others do – contact us! In addition to reliable protection against burglary, also the factors economic efficiency, operational reliability, easy operation and compatibility with existing plants are important quality characteristics. The quality “stainless steel” itself implies a high level of resistance. The perfect resistance of stainless steel products is however only given if the material is properly processed and finished. We have been manufacturing almost exclusively from the material stainless steel for more than 45 years and are therefore a stainless steel supplier by conviction! The result of these many years of focusing on stainless steel is a production that is completely tailored to processing this material and includes an integrated pickling bath to form a passive layer. This passive layer is the requirement for the corrosion resistance of stainless steel over many years. Act now! Especially remotely located well shafts are under constant threat of unauthorized manipulation. Beside careful manufacture and matured product design, the material stainless steel ensures high mechanical strength. Stable equipment will more likely deter burglary attempts and resist long enough![...]

[...]In September 2015, new standards went into force which for the first time refer explicitly to manhole covers made of stainless steel: DIN EN 124-3:2015-09, manhole tops and gully tops for use in vehicular and pedestrian areas Compared to the previous DIN EN 124, several additional tests have been added, such as: Securing of the cover / grating within the frame Skid resistance test Tipping behaviour test, etc. From 2017 on at the latest, relevant products must comply with the new DIN EN 124 standards. Since the transitional period has begun already, it is recommendable to prepare tender specifications in compliance with the new standards already now. We as a manufacturer and exporter of manhole covers have made ourselves familiar with the new situation at an early stage already and have meanwhile transferred all new regulations to all our products. In August 2016, our manhole cover type SD7 was therefore tested to the requirements of DIN EN 124-3:2015-09 by MPA Bremen (German institute for materials testing). HUBER manhole covers SD7 now comply with the latest standards and regulations and thus provide maximum security. Due to our many years of experience in processing stainless steel combined with the final surface treatment in a pickling bath for passivation, HUBER products also guarantee maximum ageing resistance. Do not hesitate to contact us![...]

[...]Guelph, Canada “Nothing slips by the RakeMax®. Its operation is absolutely flawless. After three years, we look at the components in amazement because they are ageless – it’s as if they were just installed yesterday.” Majde Qaqish, Project Engineer for the City of Guelph WWTP It had become obvious to The City of Guelph that it was time to replace several of the components in its treatment process. Project leaders also wanted to take the opportunity to upgrade its treatment processes by implementing leading edge technology. Working with consultants, the City thoroughly researched solutions to identify, review, and choose the technology and vendor that was the best match for the plant and the long-term wastewater treatment goals of the City. After visiting implementation sites, talking to other Huber clients, participating in demonstrations of technology and vendors, the City confi dently selected HUBER and the RakeMax® bar screen. The City of Guelph installed four RakeMax® screen systems over 3 years to complete a configuration that produces 100% uptime. Two systems are in production at all times with two reserved for backup. The City maintains 100% capacity through regularly scheduled cleanings and maintenance checks. Minimum maintenance Incredibly high uptime Consistent performance Ageless durability Flawless operation Challenge: For Majde Qaqish, Project Engineer for the City of Guelph Wastewater Treatment Plant, putting a leading edge screening system in place was a priority. He had a set of stringent performance and durability requirements for the technology itself and wanted to combine those with productivity priorities for the maintenance crew. The City of Guelph required four things of its technology and vendor: 1. Improve the amount of waste removed from the stream 2. Operate efficiently with little required maintenance 3. Last well into the 50 year strategic wastewater treatment plan 4. Support the technology with knowledgeable, and responsive resources Solution: Majde knew HUBER and its local support resources. He understood the RakeMax® technology and – after seeing it operate at another treatment plant – considered it to be the best technology of its kind and the best choice for Guelph’s needs. With expectations set for its new technology to produce good efficiency in removing inorganics and grit from the stream, the City was delighted when the system was even more impressive, producing at high removal efficiency, zero-maintenance operations and consistently flawless performance. According to Majde, there is a tremendous quality improvement in what gets extracted at the headworks. As a result all tank capacity is made available for optimizing plant capacity. Made to be a workhorse The design, manufacturing, and materials make the RakeMax® incredibly durable and maintenance free. It consistently out-performs other technology. The RakeMax® is also configured for easy processing. Screen covers on both the top and bottom reduce emitted odors by 70%. Monitoring screenings is as simple as lifting the covers. Low maintenance Grit tank cleanings – previously performed by the City’s crew on 2-month cycles – are now performed on 9-month cycles. Low downstream impact Debris no longer collects in digesters and their operational efficiency has shown a 90% improvement. Improvements across the screening process Marked improvements are obvious in all areas the City’s screening process. The volume of screenings removed has increased, quality of end-product has improved and unscheduled maintenance needs have been reduced to zero. Operator Quotes: “We have 100% confidence in our technology and our vendor. The RakeMax® operates flawlessly and HUBER’s resources are close by and knowledgeable of the technology and our processes.” “The odor reduction is significant. The staff faced very offensive odors when entering the area. The covered screens block any odors that exist, however the process eliminates so much of the waste that the process’s ‘trademark’ odors just don’t exist.” City of Guelph, ON - Waste Water Treatment Plant: Facilities: 1 RakeMax® Implementations: 4 Service Area: City of Guelph as well as the Village of Rockwood and the Gazer-Mooney subdivision located in the Township of Guelph- Eramosa Average Flow: 54.5 ML/d The City of Guelph, Environmental Services Department, Wastewater Services Division (WSD), is engaged in wastewater, storm water and water quality management for the area which it serves. The WSD manages and operates the Wastewater Treatment Plant located at Hanlon and Wellington Street West and is responsible for meeting the treatment standards prescribed by Ministry of Environment (MOE) legislation.[...]

[...]According to the motto "two become one", the HUBER Multi-Rake Bar Screen RakeMax® CF combines optimally matched technologies in one machine. The result is a unique screen system that impresses with both high reliability and innovative functionality. The HUBER RakeMax® CF is a modified variant of the proven HUBER Multi-Rake Bar Screen RakeMax® with a U-shaped stationary screen rack installed between the two screen frames. The bar rack is arranged in parallel to the flow direction of the wastewater. Whilst the wastewater flows into the open front side of the screen and out through both the left and right bar rack, solids are retained on the inner surface of the U-shaped bar rack. The solids retained on the bar rack lead to gradual blinding of the bar rack surface, which has an impact on the level difference in the channel. Cleaning of the screen bars starts at a defined water level in the channel upstream of the screen. The RakeMax® CF achieves this with its cleaning elements attached to the chain system. At the end of the bar rack cleaning cycle, the cleaning elements are positively cleaned by a pivoted comb, which reliably discharges the removed screenings into a downstream transport or disposal unit. The key features of the HUBER Multi-Rake Bar Screen RakeMax® CF at a glance: Proven technology of two screen designs combined into one High hydraulic throughput capacity due to U-shaped bar rack No moving parts or bearings submerged in the water Very little space required due to vertical installation - ideal for narrow spaces and deep channels Rake tines fully engaging with the bar rack Screen rake engaging above the bar rack / water surface Increased separation efficiency through flow deflection in the bar rack An emergency overflow that can be integrated as an option eliminates the need for an emergency bypass construction. This new development maintains the positive characteristics of the proven HUBER Multi-Rake Bar Screen RakeMax ® , such as high screenings discharge capacity due to a variable number of rake tines, automatic scraper device without use of process water. Due to its different design options the RakeMax ® CF covers a very wide range of applications, allowing us to respond to the individual needs of our customers and to specific constructional and hydraulic site conditions. The HUBER Multi-Rake Bar Screen RakeMax ® CF has successfully proven its functionality in various applications in daily wastewater treatment plant operation. For our customers, the optimally matched technologies in one machine result in functional advantages, especially with small bar spacings. The positive operating experience proves that once again an innovative HUBER idea from the field of mechanical cleaning has been put into practice.[...]

[...]Easy to open by a single person and made of a robust, durable material: these are features of HUBER manhole covers that have been a matter of course for a long time already. But what are other, equally important requirements on a manhole cover? 1. Meets legal regulations and normative standards HUBER manhole covers always meet currently applicable standards, thus providing safety and the required level of protection for the operating staff. All our covers raised from ground are designed and constructed according to the latest version (April 2018) of DIN 1239 ” Coverings for wells, spring water chambers and other water supply constructions ” . Our manhole covers for traffic areas type SD7 are tested and certified to DIN EN 124:2015. Also this standard has been revised and requires now that manhole covers undergo an extensive EC-type examination and an internal factory own production control at the manufacturer’s as well as regular control by a recognized body. These measures provide a much higher level of safety for operators. By the way, since March 2017, manhole covers for traffic areas must be certified to the revised version of DIN EN 124 of 2015! It is therefore especially recommended to request certifications from the manufacturer! 2. Burglar resistance – highly topical and in great demand An increasingly important point when selecting a manhole cover is sufficient and measurable protection against unauthorized access. Even the revised version of DIN 1239:2018 refers explicitly to sufficient burglary protection of manhole covers for wells, spring water chambers and other water supply constructions. Long gone are the times when “burglar resistance” was technically defined by just using a safety lock. Burglar resistance is regulated by DIN EN 1627. Considering violence-prone criminal groups, available tools and attack time, it is differentiated between the six resistance classes RC1 to RC6. The modified raised HUBER Manhole Covers SD3 and SD4 as well as the load-bearing trafficable SD7 cover have been certified to resistance class RC3 by an external test institute, thus setting new standards for burglar resistance of manhole covers. 3. Available cover sizes There is an easy answer to this question: any! We manufacture the suitable cover perfectly customized for any opening. Our standard sized are of course available within few days directly from our huge stock, such as 80 x 80 cm or 100 x 100 cm covers![...]

[...]Weltenburg, Germany In 1999, Weltenburg Abbey suffered severe damage from exceptional heavy storm floods. Also in the following years they were repeatedly faced with flood problems. In 2002, when the Abbey was restored step by step, they therefore decided to buy a flood protection system. The Abbey and the Water Management Office Landshut together with the architecture office Magerl and HUBER SE developed special flood protection elements. These elements should prevent the ingress of flood water through the nine basement windows and the 55 windows on the ground floor of the buildings along the Danube. This solution had to pass the first crucial test recently. Abbot Thomas finally was relieved to announce that the worst was over without any damage to the Abbey, thanks to all the helping hands and the new flood protection elements. The many faces of flood protection Flood damage is no exceptional case at Weltenburg Abbey as the recent flood some weeks ago has shown. According to Spiegel Online the flood in June could have been the most expensive natural catastrophe in German history. The insurance group Munich Re estimates the total damage suffered in Europe at more than twelve billion Euros. The flood destroyed not only individual houses and complete streets of houses but also public utilities, such as pumping stations, sewage treatment plants, water catchment and water distribution plants. HUBER offers most reliable flood-proof manhole covers and doors to protect all these important facilities. The use of these products prevents the breakdown of important supply and disposal facilities for the protection of the population and avoids expensive cleaning up work. No damage in Weltenburg The continuous rainfall in June this year led to a critical rise of the water level in the Danube Gorge at the "Weltenburg Narrows". But this time the Abbey was well prepared for the flood. Firemen and volunteers had installed the 55 mobile flood protection elements as a preventive measure. The flood level reached its top of 7.15 m on June 4, 2013. The installation time was very short thanks to the low weight of the individual elements. The elements are made of combined materials, namely aluminium and stainless steel. Even the biggest elements have therefore a weight of not more than 60 kg and can easily be placed in position by two persons (normally firemen). It turned out that it is absolutely uncomplicated and manageable for everyone to handle the elements. Thread rods were used to attach the elements to the window grates from inside. A round rod or screw driver served as pretensioning tools. When the flood water would rise up to the protection elements the water pressure would even increase the tightness of the elements as the sealing would be forced against the masonry walls. The firemen had received several training courses and exercised the installation of the elements several times before. Maximised efficiency of flood protection systems Water finds its path everywhere. Protection concepts must consider the rain water from above, rising levels in rivers and lakes but also the rising groundwater level. Dykes, walls, retention tanks, mobile solutions and impounding reservoirs are other elements of flood protection systems. The HUBER product range for successful flood protection comprises far more solutions than those installed at Weltenburg Abbey. We develop overall concepts to meet the requirements of each individual project. Our concepts are characterised by economic efficiency and high quality. The main focus for all applications is on the ideal price performance ratio. Other important criteria are absolutely no maintenance requirements and the reliable protection from wilful vandalism. Special structures need special solutions For Weltenburg Abbey we manufactured four different types of protection elements for the differently high windows and marked them with big coloured signs. The elements are stored on stanchions. The storage system has been determined together with the fire brigade and the architecture office. These and other measures, such as underground sealing and stop log elements on the entrance gates, will in the future prevent the Abbey from serious damage caused by flood water and preserve this unique historical ensemble for the generations to come. When we developed the flood protection solution for Weltenburg we had to keep in mind not to change anything on the facades of the listed heritage buildings. The facade itself consists of plaster which is not so plane and smooth. The sills and one jamb around the windows are made of natural stone and show tolerances of 25 to 30 mm. These tolerances could only be equalised by covering the whole window including the sill and the jamb. Due to our long experience in the manufacture of pressure doors and flood-proof doors tightness was no unsolvable problem for us. We had our prototype tested by the University of the Federal Armed Forces in Munich and they confirmed the absolute tightness of the core.[...]