Class 4 (4th Engineer) MEKG 📅 Feb 2026

Exam Question

(a) In the context of auxiliary boiler, explain, what do you understand by the term 'foaming'? List the measures you would consider to prevent it? Is it different from 'priming' in the auxiliary boiler context? (6)

(b) Explain any one of the following with a sketch: (6)

(i) composite boiler

(ii) exhaust gas economiser.

(c) What is the significance of 'de-aeration' of the boiler water? How is it achieved and what are the effects if ignored? (4)

Reference Answer

### (a) Foaming, Priming, and Prevention in Auxiliary Boilers
#### (i) Understanding 'Foaming'
Foaming is the phenomenon of persistent formation of a stable layer of bubbles or foam on the surface of the water within the boiler drum. This is distinct from the normal bubbles formed during boiling, as these bubbles do not collapse easily and build up. This condition is primarily caused by the presence of certain impurities in the boiler water that reduce the surface tension, allowing bubble walls to become stabilized.
**Causes of Foaming:**

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