The Bosch unit pump system is a high-pressure pump with separate nozzle holder assembly, providing high injection pressures for optimal air/fuel mixture. The main peculiarity of unit pump systems is their design. Like unit injector systems, they use an individual pump for each cylinder. Unlike UIS, however, pump and injection nozzle are not combined into a single unit. They represent two separate devices instead. A short line connects them with one another. The pump piston is fitted in the pump cylinder with such precision that high injection pressure is guaranteed, even at low speeds. A 2/2-way valve provides the full range of functions. The valve closes against the high-pressure circuit with the fuel feed or outlet. The injection start and duration determined by the camshaft profile can be adapted as required. As a result, the injection pressures and delivery rates required for efficient combustion are available, even at low speeds. The nozzle holder assembly is selected to match the delivery rate, spray form and injection pressure.