NOVELTY - A liquid lock device comprises receptacle containing a fermentation mass (14); receptacle cover (3) releasably interconnected with side walls (12) of receptacle forming closed space (8) over fermentation mass; at least one fluid communication conduit forming connection between space and surroundings; inner portion of fabric (2) encircling upper portion of receptacle; edge portion of receptacle cover encircling inner portion of fabric; and outer portion of fabric encircling edge portion of receptacle cover.    USE - Liquid lock device for recovery of biogas from biological material by anaerobe fermentation.    ADVANTAGE - The liquid lock device avoids too large heat losses from the tank to the cold surroundings; and let heat loss from fermentation tank go mainly through top of the tank, thus reducing or eliminating possible snow load on roof structure; and provides quick and simple dismantling of receptacle cover for inspection and cleaning.    DETAILED DESCRIPTION - The liquid lock device comprises receptacle containing a fermentation mass (14); receptacle cover (3) releasably interconnected with side walls (12) of receptacle forming closed space (8) over fermentation mass; at least one fluid communication conduit forming connection between space and surroundings; inner portion of fabric (2) encircling upper portion of receptacle; edge portion of receptacle cover encircling inner portion of fabric; and outer portion of fabric encircling edge portion of receptacle cover. The at least one fluid communication conduit is provided with first valve arranged to be able to limit the gas pressure over fermentation mass to a first gas pressure. The first valve is formed by that the at least one conduit being submerged in annular, liquid filled vessel. The fabric extends downward along exterior wall surface of receptacle wall from upper edge of receptacle and upward along receptacle cover edge portion. The outer portion of fabric is fastened to portion of receptacle cover at or above edge portion.    DESCRIPTION OF DRAWING(S) - The drawing is cross-sectional view showing a receptacle.    F fabric (2)    Receptacle cover (3)    Closed space (8)    Side walls (12)