Technical Help needed on Grasso RC912

[Jean]

We are having problem with the RC912 (R-22) oil differential pressure. The compressor starts for a few seconds then stops due to Low Oil Pressure Difference cutout RT260A.

As photo shows, we have connected a pressure gauge at the port showing a red arrow and found out that pressure is almost the same as condensing pressure (~13 bars). Is this normal? It should read suction pressure 4 bars + oil pump pressure head, approx. 2.5 bars = 6.5...

At the same Tee junction (red arrow), the other pipe goes to feed the solenoid valve capacity control (Indicate Port B on attached photo).

On GEA brochure Product Information PI2012/v008, page 35, I do not see this port?

Anyone more familiar? More experienced...

Thanks for your support.1024310244

[Grizzly]

Hi.
Unless these are hugely different from the RC11 that is the oil pressure as developed by the oil pump.
Which will and can develop way in excess of discharge pressure.
Basic stuff where oil diff is concerned,
Like-

Whats the oil like, when was it last serviced and most definitely what is the filter and strainer like?

If that fails you could look at is the oil reg valve stuck or a lost neutral on the oil diff switch?

There are many possible causes but the simplest is the most likely.
Grizzly

[Grizzly]

In fact the oil pressure at start up when read from there should be much higher.
Does the start-up time and subsequent shut down match the delay time of the oil diff switch?
Grizzly

[Jean]

Hi,

Thanks for your quick reply. Don't think there is much difference with 11 series... oil pump is not exactly the same though... different port location, but same funstion I presume.

The oil discharge pressure shown on the gauge never goes beyond 8 bars at start-up. the gauge is connected in parrale with OPD switch and after port D. However we connected another gauge at port B which is the small line carrying oil pressure to valve lifting mechanisms for capacity control/ unloading purpose.

Could it be that the 5 bars difference explained due to discharge oil filter (2) + internal tubing + pressure regulator (6) pressure drop?

The question is if oil filter ok, direct-driven oil pump ok, oil in the sump, not so clean but, same as three other compressors working fine... what could cause the pressure to drop within 20/30 seconds???

refrigerant in oil? which boils off when the compressor crankcase warms up? it's already 40degC in the machine room...

Aya !!! :confused: Must scratch my head further...

Have review electrical & timer necessary for the pressure to build up at start-up...



Hi.
Unless these are hugely different from the RC11 that is the oil pressure as developed by the oil pump.
Which will and can develop way in excess of discharge pressure.
Basic stuff where oil diff is concerned,
Like-

Whats the oil like, when was it last serviced and most definitely what is the filter and strainer like?

If that fails you could look at is the oil reg valve stuck or a lost neutral on the oil diff switch?

There are many possible causes but the simplest is the most likely.
Grizzly

[Grizzly]

Other than physical internal wear, which a strip down would need to be carried out.
I would suspect the oil pressure regulating valve.
Which is basically a spring loaded ball bearing assembly which dumps surplus oil / pressure into the sump.
After the oil has flowed through the bearings.
If this is sticking open then with no or little back pressure the oil pressure will drop like a stone.

There are other causes of cause but apart from a faulty O.P Diff switch they all are wear related.
I don't know where you are getting your oil pressure figures from?
But I would expect the oil pressure off of the pump to be way higher than 13 bar.

The simple answer is I am trying to guess your problem with little related info!
Difficult.
Grizzly

[Jean]

Hi,

Thanks for pursuing, it's nice feeling not to feel alone on this... Going to site now for internal inspection... photo to followed later today. We have "screw" open/close both regulating valve, they seemed to operate properly. Will change the main one.

Will also test the OPD switch + timer.

[Jean]

Replace both oil pressure regulators (OPR) as old one's springs were loose. Thighten the left one 10 turns clockwise and the right one 5 turns clockwise. OK?

Wonder if as the left OPR spring was very loose if it was by-passing all the excess oil back to the crankcase?

Change oil, check ODP switch... but could not run as electrical wiring issue with PLC...

Will update further next week.

[Grizzly]

Wonder if as the left OPR spring was very loose if it was by-passing all the excess oil back to the crankcase?


It definately would not help!
There is a high chance that could well be the problem.
Please let us know how you get on?
Grizzly

[Grizzly]

See attached.
The l/h is indeed lubricating pressure.
It seems to all fit into place now?
Grizzly

[cricri]

Dear Jean,
lubricating oil pressure is independant of regulating oil pressure. The RT260 protect only the lubricating oil side. Regulating oil pressure setting is Psuc+8 Bars. The lack of lubricating oil pressure can also be due to an oil leakage on the regulating side. at start up, try to run the compressor fully unloaded (1rst solenoid); if the lubricating oil pressure is then OK, it can be one of the others solenoids which is damaged or a Oring of the hydraulic actuators.
RC12 and 12E have the same system, RC11 is different with a two stage oil pump (3 gears)
regards

[Jean]

Thanks guys... Will do a test run coming Wednesday... will keep you inform.

[Magoo]

The RT260A is a straight differential switch, the time delay will be external timing by PLC or other device. The RT262AL has an adjustable differential.
If compressor fails in seconds then problem is in PLC etc.,

[Jean]

Dear cricri,

Ok for the independance operation between regulating & lubricating. But I just changed the oil pressure regulators, set the regulating one (left) to 12 turns clockwise & only 5 turns for the lubricating side. This is to ensure that most of my oil will rush to the shaft and other moving parts. Is it ok?

I will check the hydraulic actuator O-ring and the solenoid valve... try to start fully unloaded.

Thanks,

[Jean]

Hi & sorry for late reply Grizzly... no good news i'm afraid... even after changing the regulators, same things happen. We only managed to get a first good start, maintain oil pressure and run for 4 hours at 33%. Then due to no load from production side (water chilling application), they had to stop the compressor. 2 hours later they restarted, same LODP issue happened. Now back to square one....

If I got an hydraulic actuator or solenoid leaking, it will have happened during our trial test ???

GEA technical support is telling me that "The pump element is pressed to deep in the housing. There must be no gab between pump element and pump cover."... Asking for more details. You know what they mean?

[cricri]

Hi Jean,
check your Email,
go to page 42 and you'll understand what they mean.

regards