Diffuser for aeration of a fluid

An elongate diffuser comprising:

• a diffuser base comprising a diffuser body;
• a membrane attached to the diffuser body;
• wherein the membrane is connected to the diffuser body so that introduction of gas at a working pressure into the diffuser displaces part of the membrane from contact with the diffuser body to provide an elongate sealed compartment between the membrane and a surface provided mainly or wholly by the diffuser body, the compartment having a first lateral side interface region where the membrane contacts the diffuser body, a laterally intermediate region where the membrane is spaced apart from the diffuser body and a second lateral side interface region where the membrane contacts the diffuser body, and wherein gas can pass from the compartment through the membrane for aeration of a fluid in which the diffuser is immersed;
• wherein the diffuser body surface which bounds the compartment comprises a recessed portion which is recessed away from the membrane between the first lateral interface region and the second lateral interface region, compared to a planar surface extending between the first lateral side interface region and the second lateral side interface region, to thereby provide the compartment with a larger transverse cross sectional size than would be provided by a planar surface extending from the first lateral side interface region to the second lateral interface region;
• wherein a gas inlet is provided at a first axial end region of the diffuser body, and the compartment distributes gas between the inlet and a second axial end of the diffuser body;
• and
• wherein a gas inlet pipe of the diffuser provides a purge valve comprising:
• a purge control element movable between a first control position for closing a water outlet when there is little or no accumulated water to be purged, and a second control position for opening the water outlet in response to the presence of water to be purged;
• and
• a flow check valve through which water is, in use, purged, said flow check valve being a one-way valve which allows a flow of water therethrough in a purging direction and in use substantially prevents flow of water therethrough in a reverse direction.