What is a key characteristic of a positive displacement pump regarding flow as pressure changes?

• A. Flow Fluctuates Widely with Pressure
• B. Flow Increases with Temperature
• C. Flow Decreases with Viscosity
• D. Flow Remains Constant as Pressure Changes

Answer: (D)

A key point here is that a positive displacement pump moves a fixed volume with each cycle. That means the flow rate is set by how fast the pump runs and the pump’s displacement per cycle, not by the pressure in the discharge line. So as long as the pump can overcome the system pressure and operate within its limits, increasing or decreasing back pressure doesn’t significantly change the amount of fluid delivered per unit time—the flow stays essentially constant. If pressure climbs so high that the pump can’t maintain its speed or internal leakage/slip increases, you might see a small change, but that isn’t the defining behavior. This is why a positive displacement pump is characterized by flow that remains constant as pressure changes.