Grasso RC6311

[seanf]

Just wondering what is going on with the piping for the suction, intermediate and discharge headers on the RC6311 compound compressors. It looks as if some of the cylinders have all three a low stage suction, the intermediate suction/discharge and a high stage discharge connection on the cylinder. Maybe it just looks that way and is just a neater way to support the headers?

Cheers

[GrantD]

Hi SeanF

This is a compound compressor. The low stage discharges directly into the intermediate suction port. I can email you a document from GRASSO explaining the different types of interstage cooling if you wish.

[seanf]

Hi Grant,

The units I've been looking at are liquid injection on the intermediate, no economiser or intercooler.

When looking at the external of the compressor, atleast one of the high stage cylinders (top, drive motor end I think) looks like it has both a low stage suction connection and a intermediate suction connection, as well as the discharge. I was just wondering if it was just a aesthetically pleasing way of supporting the low stage suction pipe for the rest of the cylinders, or if that cylinder really does have a low and intermediate suction port thats then maybe controlled by an unloader or set up in a fixed configuration on commisioning?

4th and 5th pictures down show top drive end. https://frostyice.co.uk/product/grasso-rc6311-compressor/
Top drive end cylinder - Top right pipe is discharge, bottom right is interstage after liquid injection, top left is interstage (low stage discharge), bottom left is low stage suction.

Cheers

[RANGER1]

Shaun,
What refrigerant is compressor running?
Liquid injection sound a bit suspect, but whatever works.
Pictures with pipes on in link



Ready to run GEA - Grasso two-stage RC 6311 Compressor. - HOS BV (https://www.hosbv.com/product/6783/compressors/Grasso-RC-6311.html)

[seanf]

Hi Ranger,

Ammonia.
4 of these RC6311s with liquid injection, connected on a short length of pipe going from the low stage discharge flange of the compressor to the high stage suction flange of the compressor.

Cheers

[cricri]

Hi Seanf,

little pipes are connected only on one side. piping is the same arrangement for one stage and compound compressors.
liquid injection was a cheap solution for compound compressors, but expensive with a poor COP
Actually in most cases a liquid subcooler is inserted beetwenn LP discharge and HP suction. It works well.

[seanf]

Thanks Cricri

[seanf]

Another question.
Theres thin pipes that connect the suction to discharge headers with a cup shaped flange fitted thing, I take it there just holding a burst disk or releif valve incase theres too high a discharge pressure?

Cheers

[GrantD]

Hi Sean F,

Yes, this is an internal relief valve.

I misread or rather misunderstood your original question:

Just wondering what is going on with the piping for the suction, intermediate and discharge headers on the RC6311 compound compressors. It looks as if some of the cylinders have all three a low stage suction, the intermediate suction/discharge and a high stage discharge connection on the cylinder. Maybe it just looks that way and is just a neater way to support the headers?

The cylinders may look as if they are connected to all possible ports but if you open the heads you will find that they are blocked off internally. The same casing could be used for many configurations of single stage (RC9.11) + compound machines (RC6.3.11 or RC7.2.11).

The "short piece of pipe" you are referring to is what GRASSO refer to as the interstage gas cooler. This is Type "A'" from the GRASSO Interstage cooling type document. I can email you the relevant RC11 series manual and interstage gas cooler type if you wish (my email: grant@mre.co.za).

If you running NH3 then use a open / close flash vessel. Liquid injection may be R22 on a fishing vessel or something.

The compressor has possible water cooled head jackets. You will note that in the photo's they are plugged.

[seanf]

Thank you Grant. Ill pop you an email.

[GrantD]

Hi Sean,

Email sent. It was a large email (+/- 16MB). Check you got it.

[seanf]

Hi Sean,

Email sent. It was a large email (+/- 16MB). Check you got it.

Cheers Grant