FILTERS & STRAINERS - THERMOSTATIC STEAM TRAP PDF Print E-mail
Written by Norrie   
Tuesday, 11 May 2010 19:22
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FILTERS & STRAINERS
FILTERS
STRAINERS
STEAM TRAPS
MECHANICAL STEAM TRAP
THERMOSTATIC STEAM TRAP
THERMO-DYNAMIC STEAM TRAP
EJECTOR SYSTEMS - INTRODUCTION
EJECTORS AND EDUCTORS
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2. THE THERMOSTATIC STEAM TRAP (Balanced Pressure Trap)

This type of steam trap has a sealed, internal bellows element filled with a liquid which has a boiling point about 25°C below that of water. Heating or cooling of the element causes it to expand or contract. The bottom of the element is connected to a valve which fits into a seat in the trap body.

When the trap contains steam, the bellows is expanded by boiling the liquid inside and the valve is closed. As condensate fills the trap, it cools and the bellows begins to contract as its internal liquid stops boiling. This opens the valve and the liquid is drained off and then replaced by steam. Once again the bellows expands and closes the valve.

For the brief time taken for the expansion of the bellows to take place, a small amount of steam escapes from the trap. Variations in steam system pressure will cause a change in the boiling point of the liquid in the bellows thereby automatically adjusting the internal pressure compared to the steam pressure. Hence the trap being called a 'Balanced Pressure Trap'.


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Figures: 29