... due to water pressure difference , well safe and secure ,no noise , with out need human to operate or maintain and ... ,the flow rate depend on water pressure . C) Great tightness ,no leak ,advoid back flow , back presure go up , better performance ... 21404010022597225250200225270200401503204727534026527536026550200375197338420325338450325502504752474005204254005604257530056Clamp Type Rubber Back valve