What mechanism is adjusted to control the flow in a plunger pump?

In a plunger pump, the mechanism that is adjusted to control the flow is the plunger travel length. This is because the plunger's movement directly correlates with the volume of fluid being displaced with each stroke. By altering how far the plunger travels during its stroke, operators can effectively change the amount of liquid that is pumped, thereby controlling the overall flow rate. This adjustment is crucial for ensuring the pump operates efficiently and meets the specific requirements of the sewage treatment process.

The other mechanisms listed do play roles within the pump's operation, but they do not serve as the primary means for controlling flow. For instance, the connecting rod is vital for translating rotary motion into linear motion for the plunger but does not directly influence the flow rate. A throttle valve may be used in other applications to control fluid flow by restricting it, but in the context of a plunger pump, it's not the primary control method. Similarly, while discharge pressure is an important indicator of pump performance, adjusting it does not directly control flow but rather responds to how the system is designed to manage pressure and flow dynamics.