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STEAM TRAPS: HOW DOES IT WORK

Mechanical and Smart Steam Traps in Motion.

A steam trap is a device used to discharge condensate with a negligible consumption of live steam to save quality of steam required by the system. We know three major families of steam traps with different working modes:

• Mechanical or with float steam traps, opening and closing cycles depends to the condensates level or the density difference between condensates and steam.

> Mechanical steam traps in motion:

• Thermostatic steam traps (bimetallic, bellows, dilatation) reacting to temperature variations of fluids.

> Thermostatic steam traps in motion:

• Thermodynamic steam traps (with disc) have opening and closing cycles caused by the fluid pressure variations (fluid dynamics) or by the difference of energy between steam and condensates.

> Thermodynamic steam traps in motion:

The flashing phenomenon

Part of the evacuated condensates is transformed into steam. Sometimes it can be confused with a live steam leak. However it is not because it normally happens in regular motion of the steam trap.

How can we explain it?

The saturation temperature upstream is higher than the saturation temperature downstream. The hot condensates evacuated by the steam traps know a brutal cooling and exchange calories with the ambient conditions. The condensates are transformed into steam by consuming the calories available.

In the case of a steam trap which discharge to atmosphere the phenomenon can lend to confusion because steam at atmospheric pressure occupies 1600 times the volume occupied by liquid water.

Phenomena of blocking (blocked closed/blocked open) and problems

a. Blocked closed

Under normal functioning, the pressure upstream is higher than the pressure downstream. It is what allows the condensate evacuation. When the ΔP becomes insufficient, the steam trap cannot evacuate any more. A bad position of the adjustment device or a seal of foreign materials like calamine can also cause a blocking.

Problems:

b. Blocked open

A bad position of the adjustment device can maintain the steam trap always open. Thus the steam trap discharge live steam.

Problems:

In a general way, defective or misadjusted steam traps can reduce the outputs, increase the maintenance costs and counteract the conformity with environmental standards (ISO 14001, emission standards, etc…).



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