The Bosch VE has comparatively few moving parts, but what does move does so in a complex way. The figure to the left is from a Yanmar pump, which works and looks the same as the Bosch . On the leftmost end in the picture is the fuel feed pump. This is a vane pump, just like the vacuum pump on the VW diesel engine. Its purpose is to suck fuel from the tank and deliver it to the metering pump. All the things shown on the right in the figure have to do with the metering, timing and distribution of fuel delivery. The figure below shows this part in detail.

The plunger (right middle in the figure) in the VE pump both rotates along its axis and performs a reciprocating translation in and out. It is the translation that performs the high pressure pumping, while the rotation is responsible for metering and sending the fuel to the correct cylinder.

The cam disk is rigidly attached to the plunger. The drive shaft rotates the cam disk. The cam disk rides on four rollers (only one shown in this picture), and has four lobes. Thus for each revolution the plunger will pump four times. Note that with this arrangement the plunger stroke is constant. The metering (regulation of how much fuel is delivered) is done not by changing the mechanical stroke, but by spilling some of the fuel through spill ports, and thus changing the effective stroke . This is done by uncovering a spill port under the control sleeve at a particular angle of rotation. The other purpose of the rotation is to deliver the fuel to the correct cylinder. This is done by having four four delivery valves (only one shown in the figure), one for every 90 degrees of rotation. During a full revolution the plunger makes four strokes, one at 0, 90, 180 and 270 degrees. During each stroke the delivery port in the middle of the plunger is connected to a particular delivery valve.