Steam traps are important items in a building infrastructure, but many owners do not prioritize their maintenance. However, proper maintenance of steam traps can reduce their failures to just 3% – 5% (or less). And, a failed open trap can mean steam losses of 50 to 100 lb/hr.
Steam Trap 101
Steam traps are automatic valves that release condensed steam (condensate) from a steam space while preventing the loss of live steam. They also remove non-condensable gases from the steam space.
Steam traps are designed to maintain steam energy efficiency for performing specific tasks such as heating a building or maintaining heat for process. Once steam has transferred heat through a process and becomes hot water, it is removed by the trap from the steam side as condensate and either returned to the boiler via condensate return lines (ideal) or discharged to the atmosphere (wasteful).
Types of Steam Traps
Steam traps are commonly classified by the physical process causing them to open and close. The three major categories of steam traps are 1) mechanical, 2) thermostatic, and 3) thermodynamic. In addition, some steam traps combine characteristics of more than one of these basic categories.
Common Causes of Failure
Excluding design problems, two of the most common causes of trap failure are oversizing and dirt.
- Oversizing causes traps to work too hard. In some cases, this can result in blowing of live steam. As an example, an inverted bucket trap can lose its prime due to an abrupt change in pressure. This will cause the bucket to sink, forcing the valve open.
- Dirt is always being created in a steam system. Excessive build-up can cause plugging or prevent a valve from closing. Dirt is generally produced from pipe scale or from over-treating of chemicals in a boiler
Checklist Indicating Possible Steam Trap Failure
- Abnormally warm boiler room.
- Condensate received venting steam.
- Condensate pump water seal failing prematurely.
- Overheating or underheating in conditioned space.
- Boiler operating pressure difficult to maintain.
- Vacuum in return lines difficult to maintain.
- Water hammer in steam lines.
- Steam in condensate return lines.
- Higher than normal energy bill.
- Conduct regular testing based on pressure. High-pressure traps (250 psig or more) – daily/weekly testing. Medium-pressure traps (30-250 psig) – weekly/monthly testing. Low-pressure traps – monthly/annual testing
- Typically, traps should be replaced every 3-4 years. When replacing, take the time to make sure traps are sized properly.
- Every operating area should have a program to routinely check steam traps for proper operation. Testing frequency varies but should at least occur annually.
- All traps should be numbered and locations mapped for easier testing and record-keeping. Trap supply and return lines should be noted to simplify isolation and repair.
- Maintenance and operational personnel should be adequately trained in trap testing techniques. Where ultrasonic testing is needed, specially trained personnel should be used.
- All traps in closed systems should have atmospheric vents so that trap operation can be visually checked.
- Proper trap design should be selected for each specific application. Inverted bucket traps may be preferred over thermostatic and thermodynamic-type traps for certain applications.
- It is important to be able to observe the discharge from traps through the header. Although several different techniques can be used, the most foolproof method for testing traps is observation. Without proper training, ultrasonic, acoustical, and pyrometric test methods can lead to erroneous conclusions.
- Traps should be properly sized for the expected condensate load. Improper sizing can cause steam losses, freezing, and mechanical failures.
- Condensate collection systems should be properly designed to minimize frozen and/or premature trap failures. Condensate piping should be sized to accommodate 10% of the traps failing to open.
*Source: Department of Energy, Operations and Best Practices Guide Release 3.0, August 2010, Chapter 9.3
CM3 does provide steam trap maintenance as part of our HVAC system maintenance services. Please reach out for more information.