Abstract: A cylinder and sleeve combination, such as those found in fluid control devices, having closely positioned moving elements that leach one or more substances upon sustained contact with the subject, reactive fluid. One embodiment comprises a metering pump which utilizes small clearances that were heretofore unacceptably tight for the applications disclosed. The materials used to form at least one of the moving elements allow a substance to leach out of the moving elements as a result of a chemical reaction with the fluid, and the leached substance undergoes a separate reaction with the fluid which causes it to coagulate. The various embodiments of the present invention avoid binding of the moving elements by providing at least one scraping edge which continuously scrapes away the coagulum forming between these elements. The scraping edge is advantageously configured so as not to interfere with the operative movement of these elements.

Abstract: A cylinder and sleeve combination, such as those found in fluid control devices, having closely positioned moving elements that leach one or more substances upon sustained contact with the subject, reactive fluid. One embodiment comprises a metering pump which utilizes small clearances that were heretofore unacceptably tight for the applications disclosed. The materials used to form at least one of the moving elements allow a substance to leach out of the moving elements as a result of a chemical reaction with the fluid, and the leached substance undergoes a separate reaction with the fluid which causes it to coagulate. The various embodiments of the present invention avoid binding of the moving elements by providing at least one scraping edge which continuously scrapes away the coagulum forming between these elements. The scraping edge is advantageously configured so as not to interfere with the operative movement of these elements.