Questions and Answers
Why are steam-tight glands necessary on turbine shafts?
To prevent steam leakage along the shaft
What is the purpose of carbon segments in the sealing rings?
To prevent steam leakage around the outside of the ring
What is the function of the garter spring in the carbon sealing rings?
To hold the assembled segments together and to keep them on the shaft
Why are labyrinth glands used in high output machines operating with high temperature and high-pressure steam?
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What is the purpose of keeping a narrow clearance between the turbine shaft and casing in labyrinth glands?
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Study Notes
Lubrication System
- Excess lubricating oil is supplied to turbine bearings to carry away heat conducted from the steam space and maintain safe working temperatures.
- The lubricating oil system is driven by a gear-driven oil pump from the main turbine shaft, supplying oil under pressure for positive bearing lubrication.
Oil Flow Path
- High-pressure oil from the oil pump branches off to the governing system for turbine speed regulation.
- The oil then passes through a relief valve to prevent overpressure, and then through an oil cooler to reduce its temperature.
- The oil pressure is reduced by a pressure reducing valve (PRV) to a suitable level for bearing lubrication.
- The lubricating oil then feeds through both high-pressure (H-P) and low-pressure (L-P) bearings before returning to the oil tank.
Carbon Sealing Rings
- Small turbines use carbon sealing rings for shaft sealing, as shown in Figure 3.
- Segmental carbon sealing rings are used for steam glands on the turbine shaft, as shown in Figure 7.
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