Question 14 QMED03 - Oiler

The Correct Answer is A. ### Why Option A is Correct Condensate pumps are designed to handle very low Net Positive Suction Head Available ($\text{NPSH}_\text{A}$) because the condensate they pump is often close to its saturation temperature (the boiling point at the existing pressure). If the pressure drops too much, the water will flash into steam, causing cavitation which rapidly damages the pump. To maximize the $\text{NPSH}$ required by the pump and minimize the chance of cavitation, the first stage (suction stage) impeller of a condensate pump is always designed to be an **NPSH-maximizing impeller**. This design involves: 1. **Large Suction Chambers:** These provide a smooth, low-velocity path for the fluid into the impeller. 2. **Large Impeller Eyes (Inducers):** The "eye" is the inlet opening of the impeller. Making this eye very large, often significantly larger than standard pump impellers, allows the fluid to enter with minimal pressure drop and velocity increase. These two features—the visibly large inlet (suction chamber) and the proportionally very large first-stage impeller eye—are the most distinctive visual characteristics that allow an engineer to immediately identify a pump as a condensate or $\text{NPSH}$-critical service pump. ### Why Other Options Are Incorrect **B) open impellers and power ends:** Condensate pumps typically use **closed impellers** for efficiency and higher head development. While they might sometimes use open or semi-open impellers in very small, low-capacity applications, the defining characteristic is the large suction eye, which exists regardless of the impeller type being open or closed. The term "power ends" is too general and not a distinguishing physical feature. **C) speed-limiting governors and closed impellers:** While most large condensate pumps use closed impellers, the inclusion of "speed-limiting governors" is a characteristic of the driver (like a turbine or engine) used in variable speed applications, not a defining physical characteristic of the pump *housing* or *hydraulic end* itself. Many pumps use variable speed drives without mechanical governors. **D) multiple impellers and pump shaft positions:** Many boiler feed pumps and multi-stage process pumps also have multiple impellers, making this characteristic non-distinctive for condensate pumps. Furthermore, most condensate pumps are positioned either vertically (to gain $\text{NPSH}$) or horizontally, but neither the number of stages nor the shaft position is as distinctly noticeable as the oversized suction eye designed to handle low $\text{NPSH}$.