In a Roosa Master type injection pump, what do the pistons follow to pressurize the fuel?

In a Roosa Master type injection pump, the pistons are designed to pressurize the fuel by following the cam ring. The cam ring is a key component that provides the necessary movement for the pistons. As the pump operates, the cam ring rotates, and its profile determines the stroke of the pistons. This stroke is essential because it compresses the fuel, creating the high pressure required for injection into the engine's combustion chamber. The design of the cam ring ensures that the pistons move in a synchronized manner, facilitating efficient fuel delivery.

The other components, while important to the overall function of the injection pump, do not directly influence the pistons' mechanism for pressurizing fuel in the same way. The gear assembly aids in the pump's operation by driving the cam ring but does not dictate the pressurization process itself. Similarly, the throttle plate regulates the fuel flow into the engine but is not involved in the mechanics of pressurization. The spring mechanism may provide support or return assistance for the pistons, but again, it does not perform the primary function of pressurizing the fuel. Therefore, the cam ring is the correct answer as it directly controls the movement of the pistons for fuel pressurization.