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Class 2 (2nd Engineer) MEKG 📅 Oct 2024

Exam Question

With respect to the refrigeration system on board vessels, answer the following:

(a) Why are some TEVs fitted with an external equalizing connection? (5)

(b) What is the purpose of a back pressure valve. What will be the effect if it leaks? (5)

(c) How does an electronic TEV function? (6)

Reference Answer

### (a) Thermostatic Expansion Valve (TEV) with External Equalizing Connection
**1. Principle of a Standard TEV:**
The Thermostatic Expansion Valve (TEV) controls the amount of refrigerant entering the evaporator to maintain a pre-set superheat at the evaporator outlet. This is achieved by balancing three fundamental pressures acting on a diaphragm:
* **Opening Force (P1):** The pressure of the gas within the sensing bulb, which is strapped to the evaporator outlet. This pressure corresponds to the temperature of the suction gas.

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