an accumulator type injection valve of simple construction and relatively large accumulator capacity has opposed inlet and outlet valves for alternately and intermittently communicating a single chamber with an inlet passage for receiving fuel from a pump and an outlet passage in further communication with an injection nozzle , the outlet valve being an inwardly opening needle valve responsive to fluid pressure within the chamber . in order to even further improve operating response of the injection valve , a dump valve relieves fluid pressure from the chamber below a preselected pressure .