Question 13

The Correct Answer is C ### Explanation for C (Vacuum) **C) vacuum** is correct because the efficiency of a steam turbine relies heavily on maintaining a very high vacuum (extremely low pressure) in the condenser and the exhaust stages of the turbine. 1. **The Problem:** The turbine shaft penetrates the casing through "glands" (seals). If these seals were imperfect, the surrounding ambient air (which is at atmospheric pressure, roughly 14.7 psi) would be sucked into the low-pressure sections of the turbine (which operate near 1–2 psi absolute pressure). 2. **The Solution:** Gland sealing steam is low-pressure steam injected into the labyrinth seals around the shaft. This steam creates a positive pressure barrier that pushes outward against the atmosphere, preventing the ingress (entry) of air into the turbine casing. 3. **The Result:** Since air contamination is the main cause of vacuum degradation, preventing air ingress directly maintains the required high vacuum, which is essential for maximizing the steam's energy conversion. *** ### Why the Other Options Are Incorrect **A) oil** Gland sealing steam does not prevent the loss of lubricating or hydraulic oil. Oil retention is managed by separate oil seals, oil deflectors, and drain systems, which are physically separated from the steam glands. **B) air** This option is incorrect because the sealing steam does not prevent the *loss* of air; rather, it prevents the *ingress* (entry) of air into the turbine. Air is undesirable in the turbine and condenser, as it destroys the vacuum. **D) temperature** While air ingress can negatively affect heat transfer and condenser temperature, the primary purpose of gland sealing steam is pressure regulation (vacuum maintenance), not temperature maintenance. Turbine temperature is controlled primarily by the steam inlet conditions and the circulating cooling water system for the condenser.