Abstract: A mounting head with an internal by-pass valve for use with disposable cartridge filters, for purifying gases or liquids. In preparation for changing a spent filter, the valve mechanism is translated from a first, lowered position to a second, raised position. Product is thereby redirected through a bypass passageway, allowing an uninterrupted flow of gas or liquid product to the downstream appliance or instrument. Concurrent with the valve translation, the old filter is physically decoupled from the head, and a new filter is installed in its place. Retranslation of the valve to its first position, resumes product flow through the cartridge filter.