Thermostatic (operated by changes in fluid temperature)
The temperature of saturated steam is determined by its
pressure. In the steam space, steam gives up its enthalpy
of evaporation (heat), producing condensate at steam temperature.
As a result of any further heat loss, the temperature of
the condensate will fall. A thermostatic trap will pass
condensate when this lower temperature is sensed. As steam
reaches the trap, the temperature increases and the trap
Mechanical (operated by changes in fluid density)
This range of steam traps operates by sensing the difference
in density between steam and condensate. These steam traps
include 'ball float traps' and 'inverted bucket traps'.
In the 'ball float trap', the ball rises in the presence
of condensate, opening a valve which passes the denser condensate.
With the 'inverted bucket trap', the inverted bucket floats
when steam reaches the trap and rises to shut the valve.
Both are essentially 'mechanical' in their method of operation.
Thermodynamic (operated by changes in fluid dynamics)
Thermodynamic steam traps rely partly on the formation
of flash steam from condensate. This group includes 'thermodynamic',
'disc', 'impulse' and 'labyrinth' steam traps.