AB Cover

Durable cover and gasholder

The Air Blown Cover is an innovative double membrane roof with a relatively large, variable gas-storage volume, for biogas installations and other purposes. Weather variations have little effect on our AB Cover due to its shape and membrane pressure.


Variabel Gas storage volume
Suitable for all European snow- and windloads

Easy accessibility for maintenance and overhaul activities

Lowest silo load on a hemispherical construction

Low wind sensitivity and lower chance of snow accumulation due to stable construction


The standard version of the AB Cover includes:

  • An outer membrane of UV-resistant biaxial woven foil
  • An inner membrane of chemically resistant biaxial woven foil
  • A blower (or blowers) to maintain the pressure on the outer membrane
  • An over/under-pressure valve
  • A manual height gauge, to measure the gas volume
  • A gas-tightness test
  •  Supporting belts and net

Available options:

  • ATEX fans
  • One or more viewing windows
  • Skirt/ snow skirt
  • An ultrasonic / radar height gauge
  • Stainless steel column
  • Service box for purpose of inspection

Biogas roof miniature overview

Biogasdak miniatuur overzicht

Over/under-pressure valve

AB Cover with rain skirt

Biogasdak regenrok detailoverzicht

Durable cover and gasholder

Thanks to the high chemical resistance and mechanical strength of the foils, the ab cover satisfies the highest quality standards. New cutting and welding procedures enable the covers to better absorb the biaxial forces exerted on them.  When the hemispherical model is chosen the lowest possible force is put on the silo wall.

The AB Cover is a double membrane cover in which the outer cover is always pressurised. As a result, rain, snow and wind have little impact.

The AB Cover has a huge advantage over silo roofs due to its widely variable gas storage capacity and its ability to function as a cover for a digester or secondary digester, to temporarily collect gas. Of course the AB Cover conforms to all local and European environmental legislation.

Customisation for every situation

Each AB Cover is customised to accommodate the client’s wishes and external factors. The cover consists of separately installed upper and lower membranes which are manufactured from biaxial reinforced fabrics with a high-grade chemically resistant PVC coating.

Maximal variable gas storage capacity

AB Covers have an enormous gas storage capacity and are available for silos up to a diameter of approximately 45 metres. Operational pressures till 10mbar are no problem. Higher pressure can be accommodated on request. The tension straps and net support the upper and lower membranes against under-pressure situations and supports sulphur component flare-outs.

Installation of the AB Cover

The AB Cover is delivered to the building site prefabricated. If desired, assembled on site by our own assembly team (s).
The support straps (tractive force of 2500 kg) and the safety and desulphurisation net (net strength of 400 kg/m2) are installed at an angle. Service openings can also be incorporated as an option. A layer of wooden beams is unnecessary, which saves a considerable amount of money. Wiefferink has several own specially trained assembly teams. The success of your project is made possible by the extensive experience of our assembly teams gained during very diverse projects with renowned clients around the world. All our engineers are internally trained and VCA certified.


The AB Cover must be visually inspected at regular intervals. The glycol level and glycol freezing point must be checked in the over/under-pressure valve.