Class 2 (2nd Engineer) MEKG 📅 Jul 2023

Exam Question

With respect to the refrigeration system on board vessels, answer the following: (16)

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

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

Reference Answer

### (a) Thermostatic Expansion Valve (TEV) with External Equalizing Connection
An externally equalized Thermostatic Expansion Valve (TEV) is required on refrigeration systems where there is a significant pressure drop across the evaporator coil. This is common in large capacity evaporators or those using a refrigerant distributor with multiple small-bore tubes.
**1. Principle of a Standard (Internal Equalizer) TEV:**
A standard TEV operates by balancing three pressures to maintain a constant superheat at the evaporator outlet:

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