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. Its shape and membrane pressure mean that weather
influences have little effect on the AB Cover.


Gas storage volume at ø 25m is about 230% larger than in conventional designs
Lower membrane foil has 35% lower gas permeability

Easy accessibility for maintenance and overhaul activities

Lower silo load due to hemispherical construction

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

No condensed, corrosive liquid on the silo walls

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
  • Compressed air connections.
  • An over/under-pressure valve
  • A manual height gauge, to measure the gas volume

Available options:

  • ATEX fans
  • One or more inspection openings and a viewing window
  • Special edge finishes and a height gauge (winter edition)
  • An ultrasonic height gauge
  • A gas-tightness test


  • Cover and gas collection in biogas installations
  • Cover and gas collection in water treatment installations

Construction with silo isolation and outside lining

Over/under-pressure valve

AB Cover with and without silo isolation

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, and the hemispherical construction ensures low silo wall loading.

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 on it.

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.

Maximally variable gas storage capacity

AB Covers have an enormous gas storage capacity and are available for silos up to a diameter of approximately 40 metres. Operational pressures varying from 0 to 5 mbar and an under-pressure situation up to -1.5 mbar 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. 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.


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.