Method for filtering a liquid and filter device

A filter device, comprising:

• a membrane filter for filtering a liquid, the membrane filter including membranes and a gas introduction device arranged below the membranes;
• and
• a housing which laterally envelops the membranes over an entire length of the membranes and which is connected to the gas introduction device without gaps at a top of the gas introduction device,
• the gas introduction device including
• a liquid flow channel which vertically penetrates a gas collection cavity and admits the liquid into a bottom of the membrane filter, wherein the gas collection cavity is open at a base and defined by an upper wall and a lateral wall,
• a gas inlet configured to flow a gas into the gas collection cavity,
• a gas lifting channel where gas flows out of the gas collection cavity and empties the gas collection cavity, the gas lifting channel including a gas lifting inlet at a top in the gas collection cavity,
• a deflection portion connected at a bottom of the gas lifting channel and closed at a bottom side, and
• an inlet cross section arranged at a top of the deflection portion wherein a gas outflow channel is connected at a top of the inlet cross section.

A filter device, comprising:

• a membrane filter for filtering a liquid, the membrane filter including membranes and a gas introduction device arranged below the membranes;
• and
• a housing which laterally envelops the membranes over an entire length of the membranes and which is connected to the gas introduction device without gaps at a top of the gas introduction device,
• the gas introduction device including
• a liquid flow channel which vertically penetrates a gas collection cavity and admits the liquid into a bottom of the membrane filter, wherein the gas collection cavity is open at a base and defined by an upper wall and a lateral wall,
• a gas inlet configured to flow a gas into the gas collection cavity,
• a gas lifting channel including a gas lifting inlet at a top in the gas collection cavity,
• a deflection portion connected at a bottom of the gas lifting channel and closed at a bottom side,
• an inlet cross section arranged at a top of the deflection portion wherein a gas outflow channel is connected at a top of the inlet cross section, and
• a compensation inlet arranged below the gas lifting inlet to the inlet cross section, wherein the gas lifting inlet is arranged at a level of the inlet cross section or above;
• and
• wherein a blocking flow of the liquid downward runs through the compensation inlet, and
• wherein moving the blocking flow of the liquid along by the gas until the liquid fills the channel with the deflection portion and closes the inlet cross section for the gas.

A method for filtering a liquid in a membrane filter immersed in the liquid and including membranes, the method comprising:

• introducing a gas through a gas introduction device into a base of the membrane filter in successive pulses so that the membranes are cleaned wherein the gas introduction device includes a liquid flow channel which vertically penetrates a gas collection cavity and admits the liquid into a bottom of membrane filter;
• and initially
• filling a gas volume arranged below a free surface of the liquid and defined in a downward direction by an enclosed level of the liquid with the gas wherein the gas simultaneously displaces the liquid top down from a gas lifting channel until the enclosed level of the liquid drops below an inlet cross section of a gas flow out channel;
• and subsequently
• flowing the gas out of the gas volume downward through the gas lifting channel into a deflection portion connected at a bottom of the gas lifting channel and closed at a bottom side, from the deflection portion in an upward direction through the inlet cross section and through the gas flow out channel adjoining the inlet cross section at a top and flowing the gas to the free surface,
• wherein a continuous tubular upward open housing laterally envelops the membranes over an entire length of the membranes and is connected to the gas introduction device without gaps on top of the gas introduction device.