Liquid trap

[Herschmidt]

Hi guys:

I'm new in this forum, this is my first thread here, I always read your replies and I believe they are very interesting.

Now my question is, why do you have to place a liquid trap at the condenser outlet and when I have to do that?

Thanks in advance.

Hernan Schmidt

[US Iceman]

Dear Hernan,

I am assuming your questions relates to industrial refrigeration systems where mulitple condensers are used. The use of a trap in the liquid line from the condenser is to provide a liquid seal for the condenser coil. For a single condenser with two coils (two sets of connections; 2 in and 2 out) the traps are required to prevent the two coils from equalizing pressures on the outlet of the coils.

The traps should be below the condenser outlet at least 6 feet as a general recommendation. More depth is better. In some cases, if the equalizing line diameter is not large enough the receiver pressure cannot equalize with the condenser inlet pressure. If the receiver pressure is higher than the condenser outlet pressures, liquid will back up in the condenser drain lines. If the traps are not deep enough, the liquid can back up into the condenser coils. This increases the discharge pressure.

Each coil in a condenser can have different pressure losses. Even if the coils are identical. This can be attributed to the fan location or inlet discharge piping.

If the condensers are installed without traps, the coil with the lowest outlet pressure will allow liquid refrigerant to back up into the coil, or coil drain line. Here again this depends on the depth of the trap.

More pressure difference between the receiver and condenser outlets requires the deeper traps. This should be increased if the condensing pressure is allowed to decrease. At lower condensing pressures, the condenser coil pressure loss increases. This can increase the minimum trap depth.

When the liquid backs up in the condenser drain lines above the traps, the static head of liquid plus the vapor pressure of the refrigerant creates a pressure balance which allows the condenser coils to drain by gravity.

This is the short version of the answer. Traps are only required when you have multiple coils (or condensers) that drain into a common liquid drain line.

A good source of information on this topic is available through a BAC or Evapco representative for industrial refrigeration.

I hope this helps.

Best Regards,
US Iceman