Abstract: An air flow control valve, for example for control of air of a ventilating flow in a vertilation system comprises an axially extending valve casing having a venturi-shaped inner face, and an axially movable valve member movable within said valve casing to vary the air flow through the valve. In order that the control movement of the valve member may vary the volume of air flow through the valve according to the same predetermined function regardless of the pressure drop across the valve, or the system in which it is incorporated, the valve casing is shaped to compensate for the variation of the drag coefficient of the valve resulting from movement of the valve member. The invention also comprises a method for determining the required dimensions of a valve casing incorporating such correction.

Abstract: A connector for connecting lengths of metal tubing such as used for air-conditioning or central heating ducts, comprises a cylindrical end part for insertion into an open end of the tubing. In order to provide a seal between the connector and the tubing the connector has a recess containing a hollow, flexible sealing ring into which fluid can be injected to expand the ring. In order to ensure an adequate seal both before and after expansion of the sealing ring the latter has outwardly projecting sealing flanges which, before expansion of the sealing ring, make a seal due to their own inherent resilience and/or the resilience of the sealing ring, and, after expansion of the sealing ring, form a seal under compression. In one embodiment of the connector a sealing flange is adapted to fold over and lie between the respective faces of the connector and the tubing to prevent metal to metal contact between them.

Abstract: A method and apparatus of forming curved hollow elements by drawing comprising providing a die having an inlet opening, providing a punch which is mounted for rotation at a center of rotation which is in the plane of the inlet opening with the punch having a shape of a section of an annulus with a center of the annulus corresponding to the center of rotation of the punch, placing a blank over the inlet opening of the die and driving the punch into the inlet opening to shape the blank into a curved hollow element. The blank is held over the die inlet opening by a blank holder and hydraulic or pneumatic jacks are connected to the die and/or punch for moving them with respect to each other to form the curved hollow elements.