A back pressure regulating valve, comprising: a valve body having a fluid inlet, a fluid outlet, and a central bore disposed between the fluid inlet and the fluid outlet; a bonnet coupled to the valve body and housing a load spring operatively coupled to a diaphragm, the diaphragm cooperating with a portion of the valve body to form a chamber, the chamber in flow communication with the fluid inlet via a port; and a valve cartridge disposed in the central bore of the valve body, the valve cartridge including: a housing sized to fit within the central bore, the housing including a first portion, a second portion, a valve guide, and a flow passage positioned to provide flow communication between the chamber and the fluid outlet; a valve seat disposed in the housing along the flow passage and between the first portion and the second portion; a valve plug disposed in the housing and shiftable between an open position permitting flow through the flow passage and a closed position preventing flow through the flow passage, the valve plug including a portion engaging the valve guide; a spring operatively coupled to the valve plug and arranged to bias the valve plug toward the open position; and characterized in that the valve cartridge further comprises a retainer disposed adjacent the first portion of the housing and engaging a portion of the valve plug to retain the valve plug in the housing, the retainer comprising a spring arranged to bias the valve plug toward the valve seat. a valve body having a fluid inlet, a fluid outlet, and a central bore disposed between the fluid inlet and the fluid outlet; a bonnet coupled to the valve body and housing a load spring operatively coupled to a diaphragm, the diaphragm cooperating with a portion of the valve body to form a chamber, the chamber in flow communication with the fluid inlet via a port; and a valve cartridge disposed in the central bore of the valve body, the valve cartridge including: a housing sized to fit within the central bore, the housing including a first portion, a second portion, a valve guide, and a flow passage positioned to provide flow communication between the chamber and the fluid outlet; a valve seat disposed in the housing along the flow passage and between the first portion and the second portion; a valve plug disposed in the housing and shiftable between an open position permitting flow through the flow passage and a closed position preventing flow through the flow passage, the valve plug including a portion engaging the valve guide; a spring operatively coupled to the valve plug and arranged to bias the valve plug toward the open position; and characterized in that the valve cartridge further comprises a retainer disposed adjacent the first portion of the housing and engaging a portion of the valve plug to retain the valve plug in the housing, the retainer comprising a spring arranged to bias the valve plug toward the valve seat. a housing sized to fit within the central bore, the housing including a first portion, a second portion, a valve guide, and a flow passage positioned to provide flow communication between the chamber and the fluid outlet; a valve seat disposed in the housing along the flow passage and between the first portion and the second portion; a valve plug disposed in the housing and shiftable between an open position permitting flow through the flow passage and a closed position preventing flow through the flow passage, the valve plug including a portion engaging the valve guide; a spring operatively coupled to the valve plug and arranged to bias the valve plug toward the open position; and characterized in that the valve cartridge further comprises a retainer disposed adjacent the first portion of the housing and engaging a portion of the valve plug to retain the valve plug in the housing, the retainer comprising a spring arranged to bias the valve plug toward the valve seat.