The purpose of a Steam Trap is to keep steam in the system while removing condensate (water) and air. Air can reduce the heat transfer ability of steam and cause corrosion. Condensate / Water substantially reduces heat transfer and the ability of a steam device to do work. When a steam trap fails, it allows steam to blow-through along with the condensate. This loss of steam can represent a substantial energy loss.
There are several types and manufacturers of steam traps. The most common is the Mechanical Trap. Mechanical traps operate by using the difference in density between steam and condensate. The Inverted Bucket is the most common mechanical trap. The float resembles a bucket (4).
A float (4) within the trap detects the variance in weight between a gas and a liquid in the chamber (1). Condensate comes through the inlet (3) and the mechanical action (2) drains it out the drain (5)
The steam trap shown in the first graphic is a moderate industrial sized trap.
The most common residential steam trap is the Thermostatic traps detect the variation in temperature between steam and condensate at the same pressure. The sensing device operates the valve in response to changes in the condensate temperature and pressure.
Thermodynamic Traps use volumetric and pressure differences that occur when water changes state into gas. These changes act upon the valve directly.
For more information on Steam Traps, see the Armstrong International web site www.armstronginternational.com
Source: Text Bob Fegan Rev. 12/2008; images from Armstrong International web site;