During system operation, traps separate steam from the condensate and remove condensate properly from the system. During start-up, the traps help extract unwanted air from the system.
Although steam trap models are fully tested and highly reliable, any steam trap will eventually fail after long operation. Some of the problems might occur in the trap itself. System complications can also impair the function of the steam trap.
The most common trap problems include:
Steam trap malfunctions and failures will result from either system operation or system design problems. These conditions include:
With inverted bucket traps, dirt can plug the vent hole in the top of the inverted bucket. This allows air to be trapped in the top of the bucket and close the trap. Strainers should be used ahead of the trap and maintained to reduce dirt being carried into the trap.
Usually water hammer occurs at points of pressure change, lifts in the return line, or at traps that discharge into pressurized return lines. The situation can be corrected by installing check valves after traps that have lifts in the return line or discharge into pressurized lines. (See Figure 1.)
In these situations, a solution may be separate air vents that vent the air to gravity returns or atmospheric conditions.
As part of routine system maintenance, it is a good idea to check steam traps system-wide on a regular basis. Here is a step-by-step plan:
1. Start by creating a plan showing all buildings and sites to be inspected.
2. Mark all steam traps with a number on a drawing or schematic.
3. Attach a metal tag with the corresponding number on all traps to identify them permanently.
4. In making a record of all the traps, include information about each trap’s manufacturer, type, model number, orifice size, and application.
5. Next, make sure the system steam is on.
6. Note the steam supply pressure and check to see that the steam traps’ seat pressure ratings are correct.
7. Verify that installed traps actually are recommended for the types of applications they are carrying out.
Now, testing can begin.
For thermostatic traps:
For float and thermostatic traps:
Bucket and inverted bucket traps:
Thermo disc traps:
Rapid cycling or machine gunning indicates a worn seat and wasted steam. A cold trap means the trap is plugged or has failed closed.
Written by the staff of ITT Industries’ Little Red Schoolhouse, a training facility in Morton Grove, IL. This article appeared in “Tech Talk,” a publication of the company’s Fluid Handling Unit. For further information, call 847-966-3700.