GEA Grasso Y compressor

Would anyone have any documentation on Grasso “Y” capacity control & VSD operation.
Usually minimum speed on start, load compressor with slide valve, when 100% load increases speed on VSD to maximum speed or as required.
Same when reducing capacity, lower speed, when at minimum speed unload with slide
Valve.
Is this correct, or any concerns with excess oil in compressor?
What would be minimum speed on these machines?

Thanks

Hi Ranger,

Speed range: 1,500 to 3,600 rpm
https://www.gea.com/en/products/gea-lt-series.jsp

Attachment 15301

Hi Ranger,

you are right about the load and unload sequence for a compressor operating on VSD. there is no spécial prescription about oïl injection but better to have it well adjusted at max speed. discharge temp will then decrease at low speed.
you have to take care of the zero flow slide valve position. this position is calculated and indicated in the technical specification of the unit. (ie: see attachement).
This is the theoretical value but depending of the condition of the compressor (rotor and casing) this value can be higher.
operating at zero flow with a spring operated check valve at suction will cause a Noisy operation as no gas will flow out of compressor. With a hot gas operated check valve oïl flow back to suction.

IThanks all, so with -12 sst & 35 sct ammonia is there a minimum slide position at minimum speed 1500 rpm?
I currently do not have Comsel, is that where I could get the same info as yourself cricri.

Thanks

Attachment 15304
Comsel is obsolete since 2014. you have to use RT sélect. I did the calculation, attached Pdf.
Vi is optimum, in this case min slide valve position is 8% (10% at -15/38) at min speed.
of course it's for a new compressor, wear could need an higher value.

Quote:

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Originally Posted by cricri

Attachment 15304
Comsel is obsolete since 2014. you have to use RT sélect. I did the calculation, attached Pdf.
Vi is optimum, in this case min slide valve position is 8% (10% at -15/38) at min speed.
of course it's for a new compressor, wear could need an higher value.

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Thanks again cricri.
We have a plant where the installation company has a few different ways they control things.
I think with the VSD on this Grasso they are following Frick VSD strategy, as they can potentially reduce down to 800 rpm & have serious oil compression issues causing damage.
They also have if oil pump runs & does not achieve oil pressure or minimum load position it cannot be started for another 10 minutes, compressor never ran(possibly to let oil drain from compressor).
This is on Grasso, Mycom, Sab202.
Fairly painful to have to wait 10 minutes each time a hiccup occurs.
Usually these days with soft start or VSD it's a pretty gentle start compared to DOL or star delta etc.