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Peter_1
05-05-2004, 05:28 PM
Attached 2 pictures of swollen copper tubes I got from a colleague of me.

Machine is a 2 stage system, Bitzer, R404a, 5 compressors, 1 always in standby.
TV= -40C, TC= variable but now minimum 25C (AKC25H5 is used)

Copper was swollen after and before the NRV from compressor 2 and 4.

Fact was that machines was overfilled with oil, SH on the moment one of the copperlines exploded (compressor 4) was 2 to 5 K. They also discovered that the DANFOSS AKC25H5 the short switchings (range 1 to 5 sec) of the pressure switches hasnt recorded whereby its possible the compressor went out and on very shortly.

Discharge header dismantled and nothing strange found.
Thickness of the copper tubes is same as normal used (+/- 1,2 mm.)

After examining the setup, they found that the very low SH was only and due to an AKV on an ice machine. The SH dropped to 2K when ice machine was working.

After the collapsing of discharge 4, they repaired it temporarily with normal copper (grey tube) which is thineer then the factory discharge tube.
Also this tube has swollen again (see picture)

You can see that also the copper after the NRV is swollen (picture 1, the vertical section of teh discharge line), not only the soldering.
And also the tube between compressor discharge and the NRV, the cracks just after the shut off valve on the compressor comes from the expanded copper line.

On the suction accumulator was on the bottom a drain connection for the oil with an SV. This SV was apparently not connected.

They changed the HP switch (KP Danfoss) with automatic reset to a version with manual reset.

1 Oilfloat functioned not properly and was changed.

Because they measured on 1 compressor higher discharge temperatures, they changed the valveplate of that compressor.

No is everything working normal.

Oil was drained out of the oil cylinder.

Andy
05-05-2004, 09:47 PM
Peter :)
a little disturbing, before the check valve I could say Hydraulic action had taken place. I am now in possesion of a neat slide calculator, from D&W this calculates allowable pressure and copper thickness depandant on operating temperature and pressure. Maybe the copper was overheated during installation, anealing it. Or maybe it is too thin to start with, even although it is thicker than normal. Liquid refrigerant would do this, possible migration from the condenser (not likly as the refrigerant would have to pass thru the check valve) or a compressor was simply started up full of liquid (you will soon know when it fails). Oil hydraulic action, maybe the most likly, with some refrigerant liquid present in it.
What do you think happened. An explosion is the next thing that I foresee happening, so I quick solution would be recommended.
Kind Regards. Andy :)