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Friobernal
03-08-2005, 12:09 PM
Hi Guys;

Ive seen in ammonia systems 2 levels (Parker) near the liquid separator. Can anybody explain me how they work, i mean what do they control?

A drawing would be welcome for my understanding

Bye

US Iceman
03-08-2005, 02:43 PM
There are several different varities of level controls used in ammonia systems.

The most common are mechancial float switches. The Parker model number for these begins with the model number LL. If the separator has only two float switches (with no refrigerant pumps attached to the separator), the higher level switch is used as a high level shut down. The electrical contacts are, or should be, wired into the main control wiring to shutdown the compressors, if the liquid level in the separator is too high. This prevents the compressors from being slugged with liquid ammonia, which can damage the compressors.

The lower float switch is normally used to control the liquid level in the separator. The electrical contacts are wired to a solenoid valve in the liquid line that feeds liquid ammonia into the separator. As the liquid level decreases, the float in the chamber drops. This causes the switch to close and energizes the liquid line solenoid valve. Liquid flows through the solenoid and then (normally) into a hand expansion valve. From here the liquid flows into the separator.

As I've described this above, this type of system would be either an intercooler (for a 2-stage compressions system), or a separator with a liquid subcooling coil within the separator vessel. Sometimes these two functions are combined in the same vessel.

You can determine what type of separator it is by following the piping. If the booster (low-stage compressor) discharge line is connected to this vessel, the vessel is an intercooler. The outlet piping would then be connected to the suction line of the high-stage compressors. The high-stage compressor discharge piping would then go to the condensers. This is a typical two-stage compression system.

If the above description is not what you have, then the vessel is probably a separator in the suction line of a single stage system (only one suction pressure into the compressors before being discharge to the condensers. Here again, follow the piping into the vessel. If the suction line comes from the evaporators into this vessel and finally goes to the compressors, it is a suction accumulator (or liquid separator in the suction line). The industry uses a lot of different names to describe these vessels.

Also look for any other piping into this vessel. It is common to find a liquid line line from the high-pressure receiver entering this vessel. If this is what you have, the liquid line is attached to a pipe coil in the separator. The pipe coil is submerged in a pool of liquid ammonia (in the bottom of the vessel). The liquid line coming out of the vessel would provide subcooled liquid to the expansion valves (hand expansion, thermostatic, etc.)

If the vessel only has a suction line coming into the vessel and going out to the compressor suction line (no liquid lines), then the two float switches are; a high level shut down (the higher float switch), and a high level alarm (the lower float switch). Again, the higher float switch shuts down the compressors. The lower float switch only activates an alarm. The alarm tells you the liquid level is rising, but the compressors are still operating. In this cases, someone needs to investigate the cause. Quickly.

If a refrigerant pump is under the separator, the lower switch may be used for a low-level alarm or low level shut down for the refrigerant pump. A low-level shut down switch shuts the pump off to prevent caviatation.

As you can see from this, there are a lot of various methods to use float switches and different reasons, depending on the vessel purpose.

Parker also has an electronic device, which uses a capacitance probe. The probe measures the conductivity of the liquid ammonia, which tells the electronic controller what the liquid level is in the vessel. The electronic controller provides the same purpose as the mechanical float switches. The model numbers for these begin with the letters ELL.

The last type is an automatic liquid drainer. Model number is ALD. This is a mechanical float switch with a strainer, solenoid valve, and hand expansion valve. This are all piped together as a single unit. In this cases, the ALD operates as a high-level float valve. When the liquid level in the float chamber increases, the solenoid valve is energized. This bleeds liquid ammonia off of the vessel/coil it is connected to. The liquid that is drained out the coil/vessel goes somewhere in the system where the extra liquid will not harm the compressors. When the liquid level decreases in the float chamber of the float switch, the solenoid valve is de-energized.

Ammonia systems can be complicated, since everyone can design the system a little differently. Always follow the piping. Where it goes to and where it came from, to figure out what the vessel is doing.

For more information on the Parker equipment go to: http://www.parker.com/refspec/

This is the website for all of the Parker refrigeration components. Commercial and industrial.

I hope this helps. Work safe!

Friobernal
04-08-2005, 01:58 PM
Thanks for the lesson Iceman, anyway im going to take my dicctionary to understand everything, but it is clear.

Kind Regards

Miguel

US Iceman
04-08-2005, 03:46 PM
Hello Miguel,

You are welcome. As I noted in the earlier post, if you follow the pipes in the system this should give you an easy way to determine what is going on in the system.

If you can obtain a descripition of vessels (a catalog or brochure) from a manufacturer, it might help you to determine the vessel purpose when you see it.

I am not familiar with all of industrial refrigeration manufacturers across the ocean, but I can provide a website link for additional information.

http://www.evapcoeurope.com/

Follow this link to the section for pressure vessels. They have a PDF file you should be ably to review. This brochure has a listing and some pictures. It does not have a lot of written descriptions for their purposes, but the pictures can help you.

One last bit of advice: People have a lot of different names for things in industrial refrigeration. If someone uses a name that is new to you, please ask them to explain.

An example is: liquid separators. or suction traps, or suction accumulators, or knock-out drums, or gravity separators. They all serve the same purpose. They separate liquid refrigerant (or oil) from the refrigerant vapor by using gravity, velocity reduction, a change in flow direction, and sometimes impingement on the vessel walls.

In other cases, a demister pad may be used. The same principles apply, but the gas velocity inside of the vessel may be higher. The demister pad is normally a wire mesh pad that is located in the vessel (at the top, or exit of the vessel). The wire mesh forces the smaller droplets to form larger droplets. The larger lqiuid droplets then fall by gravity down to the bottom of the separator.

These principles are similar for oil separators too. These are liquid separators also. Except, the oil separators may have a coalescing filter installed in the vessel. A coalescing filter provides separation of very small oil particles in the discharge gas stream. The oil particles are similar to a light mist. Very, very, very small. This helps to reduce the oil carryover (oil leaving the separator) from the separator down to several ppm (parts per million).

By the way; I like your name for these much better. Liquid separator is more self-explanatory than suction trap.

If you need any additional help. Let me know.

Best Regards,
US Iceman