the condensate return system. Because of the design of the bucket, some of the condensate within the bucket is also emptied at this time, but the bucket is never completely empty, thus maintaining a water seal over the outlet and preventing steam from blowing through the trap. The cycle then repeats.

The advantages of this kind of trap are its reliability and its general ease of servicing. It can develop leaks in the bucket, and pivot wear or the accumulation of dirt can make it unworkable.

Problems if Trap Fails Shut

If a steam trap fails shut, it acts like a plug in that part of the steam system. Condensate builds up and cools, heat transfer stops, and noncondensable gases dissolve in the water and create corrosion in the pipes and in the equipment served by the trap. If a blocked trap causes condensation to build up in a line containing active steam, the steam may push water ahead of it to form a water hammer. To visualize the effects of water hammer, think of water at 90 miles/hr colliding with the inside of a pipe. Severe damage can result.

Problems of Improper Drainage

If steam condensate is not drained properly, weight accumulates, heat transfer stops, and freezing may result. Water weighs 62.4 lb/ft3, steam at 100 psi about 0.26 lb/ft3. If a 6-in. pipe is filled with condensate rather than steam, it is carrying 12.25 lb per linear foot rather than 0.05 lb. The heat transfer problem has been presented earlier. Another problem may be the freezing of pipes, particularly if the system depends upon proper operation of the steam trap to prevent freezing.

There are four basic types of steam traps, and each requires a different troubleshooting procedure. The following sections show how each trap type operates, what can go wrong with it, and what troubleshooting procedures are recommended.

Open Bucket Traps

In the trap shown in Figure 14.6, the condensate enters through the top. Since the entering hole is at the side of the bucket, condensate flows into the body of the trap, raising the bucket and causing the valve to plug the condensate relief hole. When the bucket has raised as far as the trap frame will allow, condensate fills up the trap and finally overflows into the bucket, decreasing its buoyancy. When enough water has flowed into the bucket, it drops, opening the condensate return valve. Steam pressure then forces the condensate into

Fig. 14.6 Open bucket steam trap. (Courtesy of Armstrong Machine Works.)

Open Bucket Traps, Troubleshooting and Maintenance. The operation of an open bucket trap is characterized by its regular opening and closing. This creates a noise which can be detected with an industrial stethoscope. When a trap is first installed, the frequency of clicking should be noted on the body of the trap. If this frequency changes drastically without a corresponding change in steam pressure, the trap should be taken apart (after isolating it from live steam !) and overhauled. If the trap is not making noise and is cold, determine whether condensate is getting to the trap. If no condensate or steam is reaching the trap, check strainers, valves, and lines upstream of the trap to discover where the blockage is occurring. If condensate is reaching the trap, check the pressure of the steam coming into the trap. If this pressure is too great, the trap will not work. If the pressure is correct and the trap is not working, valve off the trap so that no live steam is coming from either the steam distribution system or the condensate return and take off the cover or remove the trap from the line. Look for dirt, worn parts, or worn or plugged orifices. It is also possible that some fluctuations in steam pressure caused the trap to lose the small amount of water in the bucket necessary for its operation (the priming). This condition can be detected if the trap is blowing live steam. Close the inlet valve for a few minutes to let condensate build up, then let this condensate into the trap and it should work.

Another problem that this trap can have is caused by the need to have the priming water in the trap at all times. The trap is automatically vulnerable to freezing if the external temperature gets cold enough and if the supply of steam is shut off. If such freezing occurs, many traps have provisions for the admission of live steam to thaw the ice.

Note: There is a difference between flash steam and live steam. Flash steam is formed when condensate at a high temperature is exposed to air at a lower temperature, and part of it "flashes" to steam. Flash steam has very little pressure and gives an irregular, undirected flow pattern. Live steam however, is steam under pressure and has a well-defined, consistent pattern. The difference is significant, since the presence of flash steam is expected, whereas live steam gives an indication that something is wrong.

Inverted Bucket Traps

The inverted bucket trap (Figure 14.7) works like the open bucket trap described above, with two exceptions. First, the trap is opened and closed by steam lifting a bucket rather than by condensate lowering it.

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