Exam Question
(a) What is the purpose of providing air pipes to tanks in the vessel? (5)
(b) Sketch an arrangement of air vent head situated on the weather deck. (6)
(c) What factors are considered in deciding the bore size of air pipe? (5)
Class 4 (4th Engineer)
SC&S
📅 Feb 2025
Reference Answer
### (a) Purpose of Air Pipes on Vessel Tanks (5 Marks)
The primary purpose of air pipes fitted to tanks is to ensure that the pressure within the tank remains at or very near atmospheric pressure under all operational conditions. This is essential for structural safety and efficient operation. Specific functions include:
* **Prevention of Over/Under Pressure:** During filling (bunkering, ballasting), the incoming liquid displaces air and vapours. The air pipe allows this mixture to be vented safely to the atmosphere, preventing a pressure build-up that could rupture the tank structure. Conversely, during emptying (pumping out, consumption), air must be allowed to enter the tank to replace the volume of liquid removed, preventing a vacuum that could cause the tank structure to collapse.
* **Overflow Indication:** Air pipes serve as a critical indicator that a tank is approaching its maximum filling level. As the liquid level rises into the pipe, the sound of the escaping air changes, and eventually, liquid will be expelled from the air vent head. This provides a visual and audible alarm to the crew to stop pumping, thereby preventing structural damage and marine pollution from spills. For this reason, vent outlets are often located in conspicuous positions.
The primary purpose of air pipes fitted to tanks is to ensure that the pressure within the tank remains at or very near atmospheric pressure under all operational conditions. This is essential for structural safety and efficient operation. Specific functions include:
* **Prevention of Over/Under Pressure:** During filling (bunkering, ballasting), the incoming liquid displaces air and vapours. The air pipe allows this mixture to be vented safely to the atmosphere, preventing a pressure build-up that could rupture the tank structure. Conversely, during emptying (pumping out, consumption), air must be allowed to enter the tank to replace the volume of liquid removed, preventing a vacuum that could cause the tank structure to collapse.
* **Overflow Indication:** Air pipes serve as a critical indicator that a tank is approaching its maximum filling level. As the liquid level rises into the pipe, the sound of the escaping air changes, and eventually, liquid will be expelled from the air vent head. This provides a visual and audible alarm to the crew to stop pumping, thereby preventing structural damage and marine pollution from spills. For this reason, vent outlets are often located in conspicuous positions.
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