Class 2 (2nd Engineer) MEKG 📅 Sep 2023

Exam Question

with respect to the refrigeration system on board vessels answer the following

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

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

Reference Answer

### (a) Externally Equalised Thermostatic Expansion Valve (TEV)
An externally equalised TEV is fitted to refrigeration systems with large evaporators or those designed with a significant refrigerant pressure drop across the coil.
**1. Principle of Standard (Internal) TEV Operation:**
A standard TEV controls the refrigerant flow to maintain a constant superheat at the evaporator outlet. It operates by balancing three pressures on its diaphragm:

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