Steam Trap Basics
Steam traps are an important part of steam systems. Their purpose is to discharge condensate from the steam lines into the condensate lines. Condensate has to be removed from the steam lines promptly for a few reasons: condensate occupying heating coils and terminal equipment takes up space reducing the heat transfer area; condensate contains non-condensable gasses, some of which can cause corrosion in the system; and condensate can build up in low portions of the steam system which can lead to water hammer issues.
Even though all traps when functioning properly achieve the same results, there are essentially three different types of steam traps: thermostatic traps, mechanical traps, and kinetic traps. Thermostatic traps rely on the temperature difference between the steam and condensate to operate. The trap opens when in the presence of cooler condensate and closes when in the presence of warmer steam. Mechanical traps operate with the buoyancy principle, and open and close based on the difference in density between the steam and condensate. Kinetic traps work based on difference in flow characteristics between the steam and condensate. High pressure steam shuts these traps, while the lower pressure condensate allows them to open.
So What’s the Problem?
No matter what type of steam trap, they are far from immune to problems. Failure is common with traps, and they should be treated as a routine maintenance items. Traps can fail from improper sizing, but more often steam traps fail because of particulate in the steam lines. Particulate build up can cause a trap to plug or prevent a trap from closing (depending on the type of trap). Other failure modes include mechanical failure by cycling or erosion of the trap seating surface (like a valve seal) over time.
Failed traps can cause several problems. If a trap becomes plugged it will inhibit the effectiveness of the terminal equipment by limiting the steam flow. If a trap leaks, it will send live steam through the condensate lines. This will result in heat lost to the surroundings. The cost of this wasted steam can add up quickly. Not to mention steam in the condensate lines can lead to water hammer.
What to do
It is important to set up a rigorous steam trap testing program to identify failed traps as soon as possible. This will not only save energy, but help prevent other maintenance issues from arising down the line. Failed steam traps can be identified several ways. The easiest way to spot failed steam traps is by looking at the condensate vent. If there is a large plume coming from the vent that did not previously exist, it probably indicates leaking steam traps. The best way to identify individual faulty traps is to use an ultrasonic leak gun. With this tool, you can assess whether a trap is leaking by the sounds the trap is making.
It is recommended that a maintenance schedule be set up to check steam traps at least yearly. In house staff can be trained to use detection equipment. Other products exist that can identify leaking traps automatically and send a notification to a central computer. This technology is especially useful for hard to reach steam traps that are hard to check manually. Be sure to talk with your natural gas providers about any steam trap projects you may be undertaking. Even though these projects often pay back very quickly, the utility will often help out with incentives for replacing steam traps or funding for a steam trap leak study.