Non-return valve for preventing back flow of waste waters

A waste waters non-return valve, comprising:

• a drain pipe having a passageway for draining waste waters from an upstream to a downstream direction, a circular seat having a predetermined diameter transversely disposed in said pipe, and a housing contiguous to said seat downstream thereof and opening into said passageway, said housing extending laterally from said seat and said passageway and having an upper wall provided with a guiding strip extending transversely with respect to the pipe and being inclined in the upstream direction;
• said passageway in the area of said housing being defined by a smooth inner wall portion whereby to prevent retainment along said wall portion of detritus carried by said waste waters;
• a shutting ball having a specific gravity lower than the specific gravity of the waste waters and a diameter larger than the diameter of the seat, said housing having a size to completely contain said ball when such is in its inoperative position, whereby said ball does not then inhibit the flow of waste waters through said valve;
• and
• means carried by said shutting ball for slidably connecting said shutting ball with the guiding strip so that the shutting ball can be moved along said guiding strip out of said housing and brought in contact with the seat, in the operative sealing position thereof, by floating on the waste waters in the case of an inopportune upstream back flow, said shutting ball being held back into the housing in an inoperative position by said connecting means and by the waste waters when the waste waters are drained in the downstream direction past said housing.