How to tell an F&T trap is working It can be misleading to use the temperature coming out of the trap in determining proper operation, because the trap discharges condensate at saturation temperature. An example of this would be, if the system is operating at 2psi and the temperature of the steam is 218°F, which is also the temperature of the condensate when the steam condenses back to water. Remember, the float responds to water level changes, not temperature. Also, because the condensate will be at saturation temperature, a percentage of the condensate discharging from the trap will flash back into steam. Therefore, the best method for checking good traps is visual inspection of the discharge coming from the trap. However, do not be fooled by the flash steam that may discharge from the trap. A good trap will discharge water with a small percentage of flash steam, while a bad trap will have virtually no water as it passes steam with a noticeable hissing noise and plumes of white clouds. When selecting an F&T trap, choose a trap that uses an “H” pattern design. This style trap has two inlets and two outlets. The extra ports are for piping convenience, but instead of plugging the second outlet, create a test station. Simply install a short nipple, a service valve and a cap; then when you want to check the trap, when the system is up and running, take the cap off, open the service valve and monitor its discharge. Trap Sizing The sizing of F&T traps is important for proper operation and longevity of the trap. Many times, I have seen line-sized traps. That is, the size of the steam pipe becomes the size of the F&T trap. The problem with this method is that the steam pipe is sized to handle steam while the trap is intended to handle only air and condensate, not steam. Remember that low-pressure steam takes up approximately 1,700 times the volume that a comparable amount of water needs. This is why steam pipes are so big. The best way to make sure a trap will be applied properly is to calculate the actual condensate load the trap is going to handle. Next, apply the proper safety factor and select the lowest pressure differential that will occur across the trap. When a trap is oversized, the seat will “wire draw” because the float barely moves the plug off its seat. The steam at a very high velocity shoves the condensate out of the trap; this scores the seat so when the trap closes, the steam passes through and into the returns. ICM If you have any questions or comments please call me at 1-800-423-7187, e-mail me at gcarey@fiainc.com or follow me on Twitter at Ask_Gcarey. ICM/March/April 2016 23
ICM March-April 2016
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