Class 4 (4th Engineer) SSEP 📅 Aug 2025

Exam Question

With reference to the cargo tanks of oil tankers:

(a) State:

(i) the purpose of the pressure vacuum valve; (5)

(ii) the dangers of venting during loading via open tank hatches; (5)

(b) (i) Sketch a high velocity vent; (5)

(ii) Describe the operation of this vent and state why such a device is used. (5)

Reference Answer

### (a) (i) The Purpose of the Pressure Vacuum (P/V) Valve
The Pressure Vacuum (P/V) valve is a critical safety device fitted to the vent lines of a cargo tank on an oil tanker. Its primary purpose is to automatically maintain the pressure within the tank within predetermined safe design limits, thereby protecting the tank from structural damage due to over/under pressurization.
**1. Prevention of Over-Pressurization (Pressure Relief):**
* **Causes:** Pressure inside a cargo tank can rise due to:

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