Con Rods

[Abe]

I need some help on this query, if anyone can assist.

Compressor: L200
Make Prestcold
Duty Freezer

One con rod on this compressor broke after three months post installation. This was a reconditioned compressor

What circumstance would cause this failure?
It has been cited that as this compressor relied upon a splash type oil lubrication system, it suffered from oil starvation in the compressor body.

Is that correct?
Is that the only possible reason why the con rod would fail?

What if there was failure of the con rod itself, ie: hairline crack, or ill fitting piston which would cause the breakage

Any suggestions appreciated
Thx

Abe

[monkey spanners]

How much oil did it have in it when it failed?

What failed on the original one?

I've seen snapped rods in these due to low oil level due to shortage of refrigerant causing poor oil return, poor oil retun and snapped rod due to mineral oil and R404A, and liquid refrigerant floodback also causing snapped rods though this will often damage reed valves also.

Or if its a rebuild and an old rod has been reused, maybe it failed due to old age?

Jon

[Argus]

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Abe,

If there were a lubrication failure, you will definitely see the results on the crankshaft first in the form of striations and marks on the bearing surfaces. The presence of copper plating here will indicate a history of moisture, especially if it has used a chlorinated refrigerant (for instance, a HCFC or one of their blends).

In the absence of obvious oil loss, dilution or bearing damage, you’ll need to think outside the box, as it were.

Consider if liquid refrigerant is able to collect or to condense within the piston chamber during the off-cycle.

If this is the case, a rapid increase in temperature when the compressor resumes operation can raise the pressure of a relatively small pocket of liquid that can very rapidly develop some staggering hydraulic pressures within the cylinder and above the piston – sufficient to crack a piston of con-rod.
If the machine is fitted with a discharge muffler, you may also see distortion of the baffle plates caused by the same thing; it’s hard to spot from the outside, but if you are determined to find the cause, you need to start cutting things open.

The possible cause may be migration of refrigerant to an externally placed unit during an off cycle.
Rare, I’ll admit, but it can happen and I have seen the effect on compressors that suffer from repeated, unexplained mechanical failures.
If it is hydraulic stress, the evidence is fugitive and all you are left with are the results – i.e. broken pistons and con-rods in an otherwise unscathed compressor.


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[Abe]

Thank you Argus and MS.
Im going to think on this one.

[chris96]

I had this on a Youk recip, It had done about 30hr's after a rebuild by a very well known compressor refurbish company.
Take a close look at the conrod bolts still attached!!!

[Sledge]

Cool Pics

I havent seen a prestcold compressor in about 20 years. they didnt have a good rep back then. It is a long time ago, but if I remember correctly, there was an issue with the shells cracking.
Copeland is much more common, and has a better rep where we are.