liquid receiver low level alarm

One for the rack experts:

Beggining a few days ago, the low liquid level alarm of the receiver started to flash. I guess it is some kind of float device. It is triggered whenever the level of liquid refrigerant in the reciever drops almost to the same height of the receiver outlet pipe. I added a few kg of refrigerant, and the alarm reset, just to repeat itself the following day.
This situation did not happen before.
The only work I have been performing lately was the opening, blowing and oiling of the evaporator pressure regulating valves, and the TXVs of several circuits. But I am quite sure I did not leave ane leaks.
Some fellow told me that now that the TXVs and SORITs are working, and the TXVs are really feeding th evaporators, the liquid refrigerant that used to back off in the receiver is now flowing more freely, which translates into a lower than before liquid level in the receiver. Could this be true?

The liquid level float in the reciever is commonly wired inconjunction with a timer.(0-60minutes 1 example) it is usually situated in the lower part of the vessell.

I would not rule out that you may possibly have a leak.

With Kind regards
Mark

Quote:

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Originally Posted by racknovice

One for the rack experts:

Beggining a few days ago, the low liquid level alarm of the receiver started to flash. I guess it is some kind of float device. It is triggered whenever the level of liquid refrigerant in the reciever drops almost to the same height of the receiver outlet pipe. I added a few kg of refrigerant, and the alarm reset, just to repeat itself the following day.
This situation did not happen before.
The only work I have been performing lately was the opening, blowing and oiling of the evaporator pressure regulating valves, and the TXVs of several circuits. But I am quite sure I did not leave ane leaks.
Some fellow told me that now that the TXVs and SORITs are working, and the TXVs are really feeding th evaporators, the liquid refrigerant that used to back off in the receiver is now flowing more freely, which translates into a lower than before liquid level in the receiver. Could this be true?

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HI Rack novice.
Not much of a novice if you know how to drop the oil out of the evaps!.
If the receiver is down in the plant room where its nice and warm as opposed to the ambient temperature where the condenser is situated, You may have a problem with liquid hangup in the condenser, that is to say that the liquid doe,s not want to drain down into the liquid reciever which is at a higher pressure. The fix for this is to take a small 1/4" or 3/8" hot gas line from the compresser discharge outlet and hook it into the reciever near the top above the normal liquid level, [if you can get your gagues onto the system this will prove the problem] this will balance the pressure in the condenser and reciever which will allow the condensed liquid to flow via gravity into the reciever. The most likely time for this liquid hang up to occur is at night and just after a defrost. Good Luck Tony L.:cool:

If all TXV's are now feeding properly under normal load (by superheat), you've determined there are no other restrictions or leaks and you've adjusted the head pressure valves, then likely, you had a low refrigerant charge to begin with. this is more evident if this system uses hot gas defrost and more than, say, 20% of your systems call for hot gas at the same time causing a drop in condenser pressure. Try increasing condenser pressure before adding more refrigerant. cool?

If the rack is on 404a then liquid "hiding" in the condenser is a common problem. To check, close the outlet valve of the receiver and pump the rack down. Then open it up slowly and check the level in the receiver after an hours running, you do that by warming up the side of the receiver and feel the temp difference where the liquid is up to. Below 25% you will need more refrigerant.

http://www.refrigeration-engineer.co...ead.php?t=6804

Just found this thread on Gas defrost.

With Kind regards
Mark:)

You need to make sure you are not holding liquid up in the condenser(s). In Panama, do you use ow ambient flooding controls on the condensers or just fan cycling?

Are you doing any sort of hot gas defrost any where?

Ken

http://www.refrigeration-engineer.co...?t=6804&page=2

Meant this page the bit on ORD ORI set up.

Mark

racknovice,

The Fellow that gave you the advice that everything works better now and accounts for a lower liquid level could be true!

Another factor could be this!

When you clean the valves, were they very dirty?

What type of defrost control are you using on the racks (Multiplex)? Cam defrost timer or individual defrost timers or electronic timers staggered in groups?

Being working on a circuit at a time, with individual defrost timers, it could be that you have upset the defrost sequence on the whole plant.

This could mean that more circuits came out of a defrost at once than before, resulting in a bigger cooling demand than previously, resulting in a lower liquid level than before.

Hope this will answer some questions.