UNDERSTANDING STEAM TRAPS
United Trades Exclusive
By Tim Daly
A Major Key to Getting The Most Work Out Of Your Steam
We have previously discussed steam as being the lifeblood of industry, and we started to delve a little into the boilers that generate the steam. Today we’re going to look at one important aspect of the efficient distribution of steam. This one aspect—steam traps—can go a long way in maximizing production, and even climate control in a large industrial complex, by helping to properly maintain the steam distribution system.What Are Steam Traps, And Why Do We Need Them?
We know that steam is the gaseous form of water. We know too, that as steam cools down, it condenses back into water. When and why does it cool down?
Steam is generated by adding heat to water in a boiler. As the water in the boiler chambers is heated, both temperature and pressure increase. When the temperature reaches sufficient levels, steam is produced. When the steam reaches the desired pressure in the boiler, it is sent into the main steam header and from there it makes its way to the distribution system. As the time and distance from the heat source begin to mount, the steam begins to lose both pressure and temperature. That pressure and temperature reduction are magnified as the steam makes its way through obstructions like bends, fittings, valves, and whatever components and devices the steam is actually being used for.
As heat is being drawn away from the steam, it begins to condense. When the steam is condensing we need a way to remove the water from the steam, while allowing the steam to continue on to its rightful destination. This is where steam traps come into play.
Steam Traps are devices strategically located on a steam distribution system to remove the condensed steam (water), and also air and non-condensable gases, while trapping the dry steam and keeping it in the system.
When we say strategic locations, we’re talking about spots where the steam travel could be interrupted, like isolation or stop valves, and also where the steam lines move in a vertical direction—whenever there is a vertical rise or drop in a steam line, there should be a steam trap located at the bottom of the vertical run. The other key place for steam traps is at the steam’s entry point to a device designed to use the steam like a turbine generator, steam kettle, or sterilizer for example.
Different Types of Traps
There are several different types of traps in use to varying degrees, but we’ll list a few of the more common types and their uses here.
These traps are normally found on main steam headers, especially outside, as they generally don’t freeze up. Where other steam traps have Wye strainers installed ahead of them, these often do not as they have a Wye type strainer built into them. They have a chamber with a screen that can be blown out with the twist of a wrench, or can be removed during shutdowns for thorough cleaning. The top of the trap has a disc that will rise or open when condensate is present, allowing the condensate to escape into the condensate header while trapping the steam in the steam system.
Thermostatic traps have a fluid filled bellows in them that is sensitive to heat. When steam enters the trap, the fluid vaporizes, and expands the bellows which in turn shuts off discharge flow. When cooler air or condensate are present the in the trap, the fluid in the bellows condenses back into liquid form, which contracts the bellows and allows the condensate to flow out into the condensate system until the trap fills with steam again. These traps are desirable during system start-ups because of their unique ability to discharge undesirable air, as well as the high volume of condensate present during the start-up.
Float and Thermostatic Traps
Float and thermostatic traps—or F&T traps as they are commonly called—have a thermostatic air vent near the top of the trap that will allow air to escape from the system, even when there is not enough condensate present to allow the float to open the main discharge seat of the trap. These traps are also very desirable during start-ups because of their ability to discharge air when it is sensed.
The float within the trap operates like the float on a sump pump. As the level of condensate builds, the float rises which opens the discharge orifice. This allows the condensate to escape, and when the condensate drops below the orifice level, the float drops securing the orifice and trapping the remaining steam. These traps are most often used for condensate draining at the devices and components using the steam.
Inverted Bucket Traps
Often referred to as just bucket traps, inverted bucket traps have what looks like an inverted (upside down) bucket installed within the body of the trap. The bucket starts out in the down position, keeping the discharge open, which allows the condensate to exit the trap. When the steam becomes present it makes its way into the bucket, which will push the bucket up, therefore plugging the discharge opening and trapping the steam in the system. When the steam condenses, the bucket drops, removing the condensate until the steam returns. They do have a small bleed hole to remove some air, but it generally is not going to remove a lot of air fast.
As these traps are not known for their air handling abilities, but are very rugged allowing them to stand up well to water hammer and dirt, they are generally used on main steam lines.
Steam trap maintenance is often overlooked and under-performed. If steam traps are defective and allowing steam to pass through, therefore being vented at condensate tanks, the plant using the steam is wasting a lot of money generating extra steam to compensate for it. Conversely, if your traps are not performing their main function, then condensate is being allowed to stay in the steam system creating potentially major efficiency and safety hazards.
Paying mechanics to perform preventative maintenance on steam traps may seem like an expensive endeavor, but the money you can save on a more efficient steam system makes it well worth it.