Abstract: A heater for fluids has a main housing part which is provided with flow channels for a fluid to be heated. The main housing part is surrounded by an auxiliary housing part, and the housing parts cooperate to define a compartment which is capable of containing sparks, flames and explosions. The compartment communicates with the atmosphere via one or more gaps too narrow to be penetrated by sparks and flames. The compartment further communicates with a chamber which is provided in the auxiliary housing part for switching elements. A heating foil is adhesively secured to one surface of the compartment so as to lie flat against such surface.

Abstract: A layer of viscous material is applied to a substrate by constricting a stream of pressurized viscous material prior to entry into a chamber wherein the constricted filament-shaped stream is acted upon by radially inwardly and forwardly oriented currents of compressed air which reduce the thickness of the stream and issue with such stream from the chamber through an orifice. The orientation of air currents in the chamber is such that the filament is not imparted a swirling movement. The flow of air issuing from the chamber through the orifice forms a hollow cone which surrounds the filament of viscous material on its way toward contact with the substrate.

Abstract: Successive plate-like substrates are transported in a horizontal plane on a first conveyor beneath a first spray coating device on their way toward an inverting device which turns successive substrates through 180.degree. and deposits them on the supporting elements of a second conveyor which advances the once coated substrates beneath a second spray coating device. The twice coated substrates are advanced through a drying zone wherein they are acted upon at both sides by infrared heaters which expel the surplus of moisture. The supporting elements are in mere linear or point contact with the coated undersides of inverted substrates above the second conveyor. Such supporting elements can engage uncoated marginal portions of the substrates or the coated portions of undersides of substrates above the second conveyor. Coating material which bypasses the substrates is intercepted and collected, and the supporting elements are cleaned at regular intervals.