Sabroe SMC112

[Snowflake]

I have a problem with a SMC112 Compressor, to start off it had a problem when loading to 100%, the compressor would just switch off, no faults etc were indicated at all, i have stripped the compressor and put it all back as we thought there was a mechanical fault. we have the same thing happening, it runs fine at 33% once you switch on to 66%, it runs for about a minute and swithes off???? there is no sign of abnormal noise etc once it is off, the compressor is free at this pint it can be turned by hand.

the conditions are as follows:

Suction @ 200Kpa
Discharge @ 800Kpa
Oil Press @ 420Kpa
Motor Amperage is normal, the motor is controlled by a soft starter no fault at all is indicated anywhere??? i am thinking it may be electrical, but thought i could ask if anyone else has experienced this in the past???

Cheers

[Sandro Baptista]

Does the compressor is equipped with UNISAB?

OR

Is there no indication of any fault on the MP55, KP98,...?

[Grizzly]

Hi Snowflake.
You have not given us,to much to go on.
But because you say the problem is related to the % loading.
It just may be oil pressure related.
When you run up the machine to observe it tripping.
Would you be able to meter the oil diff switch! (or the Safety / Control circuit?).
There are a host of other options that may apply if you have Unisab Control.
Which I suspect is why Sandro has asked that question.
Tell us more as there are quite a few guys on the forum who should be able to help!

Grizzly

[josef]

Sorry-Mk?:)

[charlie n]

The correct oil pressure for an SMC is about 4.5 bar above suction. It looks like you have only 2.2 bar. This is enough pressure to load the machine but a properly set MP54 or a Unisab will stop the machine after 90 seconds. (not exactly sure if it's 60 seconds or 90 seconds) Oil pressure can be increased by adjusting the oil pressure regulating valve. This is located on the shaft end of the machine just above the shaft seal. When the compressor starts, turn the screw clockwise to achieve a higher oil pressure.

[Snowflake]

The Compressor does not have a unisab control, it is plc controlled through a scada software program, the Compressor is a Mk1.

There is no fault at all re the MP55 etc,

Charlie n - i will try this, the strange thing is the compressor has been running at these pressures for years???

Will let you know if anything else happens - results.

Cheers

Snowflake

[Grizzly]

Hi Snowflake.
You obviously are well versed with your machine/s!
So this is indeed something more out of the ordinary.
It is strange that the oil pressure is so low a reading
all the same!
I once had an old CMO recip that would shut down on loading at differing stages of load.
Which was due to excessive oil circuit clearances throughout the compressor.
The loss of lubrication pressure increased pro-rata with the loading of the compressor.
Until the comp failed!
What stage it failed at varied along with the oil temp.
Hence my original line of thought.
Is there any possibility that you could be experiencing similar?

An alternative may be that you have a electronic issue.
Sorry but i don't know the system you are using.
Does it have a run history you could interrogate?
Cheers Grizzly

[Snowflake]

hi Grizzly

thanks for the advice, we had a sparky check over the soft starter etc, nothing obvious was found, we ran the compressor and the fault has not happened again????????? very strange, they do suspect some problems within the PLC which will be looked at next week. the compressor has been loading and unloading fine, very confused as we have not pinpointed the problem just assupmtions.

with regard to the CMO you mentioned the loss of oil pressure when the compressor loaded, this does make sense, the oil pressure does not fluctuate that much when loading/unloading, but this is def something to keep in mind.

thanks

Snowflake

[Sandro Baptista]

The correct oil pressure for an SMC is about 4.5 bar above suction. It looks like you have only 2.2 bar. This is enough pressure to load the machine but a properly set MP54 or a Unisab will stop the machine after 90 seconds. (not exactly sure if it's 60 seconds or 90 seconds) Oil pressure can be increased by adjusting the oil pressure regulating valve. This is located on the shaft end of the machine just above the shaft seal. When the compressor starts, turn the screw clockwise to achieve a higher oil pressure.

Maybe is talking on differential oil pressure, despite he's talking on oil pressure. On the gauges we read directly differential oil pressure.

[josef]

Probably only one possible reason is the differential pressure switch Danfoss.
Value that is set around a small and a smaller pressure fluctuations from 33% to 66%.
The second problem is the time relay holding period from the start.
Josef.

[cricri]

Hi Snowflake,
If its realy an oil pressure problem...
The SMC 112 Mk1 is for us the first design named SMC12x100. on these Mk1, the oil pressure régulating valve can be only partially replaced. So the body is as old as the compressor (30 years?). the valve can be then stipped an lazy.
when you load the compressor a short oil pressure decrease can switch of the compressor. a bad locking of the fault and nothing appear on the PLC. the pressure gauges are normally fitted with calibrated aluminium gaskets, so the oil pressure seem OK during this short time.
solution:
- use sand paper on both valve and body of the oil pressure regulator
- insert a time delay (2 sec) when oil pressure switch set of.
I have also seen this kind of oil problems with the Mk3 oil filters clogged

[Sandro Baptista]

But...the MP55 has a time delaying from 45 up to 90 seconds...so if that effect is instantaneous nothing should happens by that way.

[cricri]

But....nothing says that the MP55 is fitted with a time delay on this SMC112.
most of our reciprocating compressors are using MP55 or RT260 without time delay, a timer ( PLC, ...) allow the compressor to start and switch it of instantly when oil pressure decrease.

[Sandro Baptista]

Cricri. I knew that RT260 hasn't time relay but about the MP55 you're right about that...there is MP55 versions that haven't time relay.

[Magoo]

snowflake.
try looking at the C/T 's on the mains supply feeding back to the soft starter. Any imbalance will be accentuated as compressor loads up. Had similar problem. The soft starter just came up with general fault, non specific.