Types of steam traps:

1. Thermostatic (temperature-operated) traps: Operate on the difference in temperature between steam and condensate. Types include:

• Balanced-pressure (bellows/ capsule) trap: A bellows/ capsule containing a volatile liquid expands/ contracts with temperature, opening/ closing the valve. Self-adjusting to steam pressure.
• Bimetallic trap: A bimetallic element bends with temperature to open/ close the valve.
• Liquid-expansion trap: A liquid-filled element expands with temperature.

1. Thermodynamic (disc) traps: Operate on the difference in velocity/ pressure between steam and condensate. A disc is lifted by condensate flow and closes when steam reaches it. Simple, robust, used for high-pressure/ superheated steam.
2. Mechanical (float) traps: Operate on the difference in density between steam and condensate. A float rises with the condensate level and opens the valve; a thermostatic air vent removes air. Used for continuous/ large condensate loads.

Selection for an oil tanker:

• Consider the steam pressure/ temperature (auxiliary boiler steam, ~7-10 bar), the condensate load, and the application (heating coils, tank cleaning, steam tracing, etc.).
• For continuous/ large condensate loads (e.g. cargo heating coils), a float trap (with thermostatic air vent) is suitable.
• For high-pressure/ superheated steam and where robustness is needed, a thermodynamic (disc) trap is suitable.
• For varying loads and where air venting is important, a thermostatic (balanced-pressure) trap is suitable.
• Consider the need for air venting, resistance to water hammer, and ease of maintenance. The trap must be sized correctly for the condensate load and the steam pressure.

Maintenance tasks:

• Regular inspection of the trap for correct operation (steam/ condensate discharge, no steam blow-through).
• Cleaning the trap and its strainer/ filter to remove dirt and scale.
• Checking the trap for leakage (steam loss) and repairing/ renewing worn parts (valve, seat, disc, float, bellows).
• Testing the trap (e.g. by listening/ temperature check, or by a test valve) to confirm it is operating correctly.
• Checking the condensate return/ discharge line for blockage.
• Replacing worn/ failed traps.

Frequency:

• Traps should be inspected/ tested regularly (e.g. monthly or at each planned maintenance interval) and cleaned/ serviced as required. The frequency depends on the service (steam quality, load) and the maker's recommendation. A regular programme (e.g. quarterly inspection, annual overhaul) is recommended.

How regular maintenance extends trap life and reduces losses:

• Regular cleaning and servicing prevent dirt/ scale from damaging the valve/ seat and causing leakage.
• Early detection and repair of leaks prevents steam loss (energy loss) and reduces operating cost.
• Proper maintenance keeps the trap operating correctly, preventing condensate build-up (water hammer) and steam blow-through, extending the trap's life and the life of the steam system.
• A well-maintained trap reduces energy losses and improves the efficiency of the steam system.