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nandoanalog
25-04-2015, 09:06 PM
Some cars have "knock" sensors to know if the combustion is happening before the piston hits tdc. Why aren't refrigerant compressors equipped with similar technology to shut off when too much liquid gets sucked?

Brian_UK
25-04-2015, 10:19 PM
Because it costs money.

Also, compressors do not have detonation in the cylinders so there isn't a knock to measure.

Rob White
25-04-2015, 11:43 PM
.

Bitzer use a probe to sense the suction temp and measures it against
the correct superheat settings and if it sense saturated vapour then
it trips out.

Rob

.

Grizzly
26-04-2015, 07:53 AM
On larger systems with obviously larger compressors.
The comps -(recips) can be fitted with buffer springs which lift to prevent Hydraulic lock / damage.
Also you can get system control where the oil temp in the sump is monitored and if the oil is colder than ambient. The comp will not be allowed to run.
Ultimately though, why should comp manufactures build in safety's to that standard.
When liquid carry over is a result of poor or bad system design / set-up!
After all if the motor is designed to take say 30 or 40amps and you subjected it to more would you blame the motor manufacturers.
J&E Hall in the 70's built a bullet proof recip that could be dropped (accidentally) from a helicopter, for military use. But was 30-60% more expensive and guess what people stopped buying them.
Cheap is now the name of the game, irrespective of who make what.
Grizzly

hookster
26-04-2015, 06:04 PM
The Frick compressor range has the option for vibration monitoring from the Quantum controller.
http://www.frickcontrols.com/uploads/versions/070.020-TB_PhD_Vibration_Monitoring_2012-08.pdf

RANGER1
26-04-2015, 08:58 PM
The Frick compressor range has the option for vibration monitoring from the Quantum controller.
http://www.frickcontrols.com/uploads/versions/070.020-TB_PhD_Vibration_Monitoring_2012-08.pdf


They also have "slug back" control", discharge temp drops suddenly, then stops compressor, as liquid must have entered compressor.

Segei
26-04-2015, 10:33 PM
I agree that drop of discharge temperature is first sign of liquid enters compressor. When compressor start knocking, it will be too late. Internal parts can be damaged.

RANGER1
27-04-2015, 04:01 AM
I agree that drop of discharge temperature is first sign of liquid enters compressor. When compressor start knocking, it will be too late. Internal parts can be damaged.

Was referring to Frick screw, still not good, but better than nothing.

hookster
28-04-2015, 07:32 AM
I have seen large screws chewing on liquid slugging and to be honest the damage is not instantaneous. They can handle a fair amount of slugging.

Or in another case I have had a lot of sea water returning to the suction. Sounded horrendous and shook like a 'wet dog'. After opening up there was no mechanical damage but after the dry out the system was a pig as it just started corroding everywhere. Clean up was Fun! :(

At the time we were doing regular ppm vibration analysis with hand held units. The fitting of constant monitoring accelerometers would have given early indication as conditions started changing.

sterl
28-04-2015, 05:04 PM
The Frick drop in discharge temp routine has a couple of issues....Combined with liquid injection oil cooling a loss of continuous liquid flow followed by a resumption will cause it to trip, and you can spend a lot of time trying to sort a liquid carryover topic when the real problem was the disruption of condenser drainage.....

Also have seen them cut out in certain climatic conditions and condenser control arrangements with the start of evaporative condenser water flow, or even HG Defrost applied to a big coil. This did get addressed, the processors now compare discharge temperature to discharge pressure to establish a rate of change in superheat rather than simply temperature....

Segei
06-05-2015, 12:56 PM
Was referring to Frick screw, still not good, but better than nothing.
It will work better for reciprocated compressors. We don't need to cool oil only gas.