Abstract: A tubular ventilator has a rigid supporting tube provided with radial bores over which a foil-like hose with superfine pores is drawn, the tube is covered at its ends by covers having center bores for connecting two gas lines, the interior of the tube is subdivided into two halves each provided with a pressure-tightly displaceable plunger.

Abstract: A process for making fine perforations in plastic sheeting and/or plastic or rubber coated sheet materials in which the sheeting or the coating is too thick and/or the dielectric constants are too high for electrically making the fine perforations, including the steps of coarsely perforating the material by non-electrical methods, coating the perforated material with a layer of a coating material which is capable of being electrically perforated, and making fine perforations in the layer of the coating material by the use of high-voltage pulses.

Abstract: Arrangement for effecting the superfine perforation of film-like sheeting with the aid of high-voltage pulses. The sheeting to be perforated is permitted to pass in a contactless manner between two areal electrode fields. The electrode fields consist of a multitude of needles which are aligned to one another in a mirror-inverted manner and arranged in rows, with each time pairs of them forming discharge or sparking gaps. The needles of the first electrode field are in a direct conductive connection with each time one high-ohmic resistor. Each needle pair is arranged within the secondary circuit of an ignition transformer. These transformers have a high transformation ratio. On the primary side, the transformers are connected via transistor switches, to a source of low d.c. voltage. The transistor switches are initiated groupwisely via a distributor (ring counter) which, in turn, is controlled by a clock-pulse generator.