The Distributor Type Fuel Injection Pump has a single pumping element. The fuel is distributed to each cylinder by means of a rotor. It is small in size and lightweight. Lets have a look at the various parts. There is a central longitudinal cavity in the rotor and a pair of radial holes at different heights One hole is for fuel inlet and other for fuel outlet. The fuel is drawn in OR forced out of the cavity as per the movement of the plungers.
The Cam Ring controls the movement of the plungers via a roller and a bush at each end. Over the rotor, there is a stator that contains inlet and outlet ports for the fuel. As the inlet passage of the rotor aligns with the inlet port, the plungers move out, drawing fuel into the central cavity.
When the outlet passage aligns with the outlet port, the plungers move inward, pushing out fuel from the cavity. Now consider an injection pump for four cylinder engine. There are four inlet passages to intake fuel four times and four outlet ports for the four cylinders.