Abstract: A slot forming a splicing chamber is closed by sliding action between contacting surfaces of two bodies linked at a point which is perpendicularly spaced from both surfaces. The closure surface comprises the crown of a piston. The piston has a central orifice and is slidable in a bore in one of the bodies to which pressurized air is admitted. When the chamber is closed the orifice registers with the slot and allows a blast of air to pass from the bore into the slot.

Abstract: Yarn splicing chambers which in one form comprise a block with an open channel therethrough, one wall of the channel being vertical and the other inclined to form an included angle of between 30.degree. to 45.degree. . An inlet is provided centrally of the bottom of the channel for admission thereto of gas under pressure of 5.5 bars to produce vortex flow having a predominant direction of rotation when, in use, the open top of the channel is sealed by a shutter, the gas exhausting out of the open ends of the channel into which yarns are introduced for splicing. An alternative form of chamber comprises a block having an open channel therethrough wherein each wall of the channel comprises a first wall portion substantially vertical with respect to a flat bottom portion of the channel at respective end portions of the channel, and a second wall portion inclined with respect to the said flat bottom portion, and the inlet means is located within the central portion of the channel.