Thread clamp, particularly for jet looms

A thread clamp for temporarily arresting a weft yarn in a jet loom, comprising:

• a housing with an apertured front wall;
• a stationary insert in said housing having a throughgoing passage substantially perpendicular to said front wall;
• a deformable first membrane in said housing defining with a front surface of said insert a first chamber adjacent said front wall;
• a deformable second membrane in said housing defining with a rear surface of said insert a second chamber remote from said front wall, said second membrane having a mobile portion wider than a mobile portion of said first membrane, said chambers communicating with each other through said passage;
• a stem traversing said passage with clearance while being fixedly secured to both said membranes, said stem projecting beyond said front wall and terminating in a movable jaw;
• a fixed jaw secured to said housing and confronting said movable jaw for contact therewith in a forward position of said stem in which said first and said second chamber respectively have a maximum and a minimum volume;
• spring means coupled with said stem for biasing same toward said forward position thereof;
• conduit means in said housing opening into said second chamber;
• and
• control means for selectively connecting said conduit means to a source of high-pressure air and to the atmosphere, admission of high-pressure air to said second chamber by way of said conduit means generating a pressure differential moving said stem into a retracted position against the force of said spring means.