About the authorEqualizing Lines on Ammonia Receivers
If you think you may have a problem with draining liquid ammonia from your evaporative condensers, you may want to investigate the equalizing line. This piece of pipe is typically installed on top of the high pressure receiver. The termination of this pipe is usually the discharge line leading to the condensers.
What follows is a brief description of how the equalizing line works.
Consider a 2 liter plastic bottle, which is partially filled with water, say half full. Turn the bottle over (neck down) and watch the water try to drain out. The water flows out by sporadic “gushes”. The reason for this is the difference in pressure across the bottle. We have atmospheric pressure on the outlet (the bottle opening); while inside of the bottle (on top of the water) the pressure is lower. During each “gush” of liquid out of the bottle, the pressure in the bottle is equalized with the atmospheric pressure by air bubbles rushing into the bottle.
This is how condenser coils drain if the pressures are not equalized properly between the high-pressure receiver and the condenser coil drain connections.
Now take the same bottle and refill it one half full with water. Place one hand over the bottle opening and turn the bottle over. Have someone punch a small hole in the bottom (now the top) of the bottle. Remove your hand from the bottle opening. What happens?
The bottle now drains more quickly and evenly. If the vent hole is too small, you may have some minor gushes of water as it tries to drain out of the bottle.
Now, try this once more. Refill the bottle about half full. Turn the bottle over, covering the opening. This time, before you remove your hand from the bottom of bottle, enlarge the vent hole. This time the water should flow very quickly out of the bottle.
The vent hole allows the air pressure to equalize on both sides of the water in the bottle so that the water can flow out by gravity. If the vent is too small, the water drains unevenly, although still much better than if no vent is provided. If the vent hole is large enough, the water runs freely. This is gravity drainage working properly.
This is the same effect we see in condenser drain lines when all of the piping is designed and installed properly.
Remember the small vent hole someone put into the bottom of the bottle? We can compare this vent hole to the function of the equalizing line from the high-pressure receiver to the condenser(s). The larger vent hole allowed the water to drain quickly without the sporadic “gushes”. An equalizing line sized appropriately provides the same function as the larger vent in the 2 liter bottle.
If you have any questions, please post it in the comment section. I’ll do my best to provide an answer.
Tags: analysis of refrigeration systems, draining evaporative condensers, equalizing lines, liquid ammonia receivers
