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engrp
06-08-2012, 11:34 PM
I am doing rehab works on our grasso rc612. we will be needing a number of o rings. however, the cost of the o ring from the oe supplier is very expensive. there are a number of o ring stores from which , i think i can purchases the o rings, but i don't know the material for the o rings. maybe, some of you who have purchased o rings for grasso recips have an idea. i looked at the compatibility chart of o rings in one website, and it says, either butyl or neoprene is compatible with ammonia. any of you have any advise ? thank you

RANGER1
07-08-2012, 08:37 AM
To keep it simple neoprene is best material for ammonia gas, liquid & oil.

A lot of Sabroe compressor "0" rings are HNBR material, probably more suitable in compressors with synthetic oils.

Mycom use Buna "N" or nitrile (same thing). in all their ammonia compressors.

Sometimes size of "0" ring dictates what size to use as well. ie You cannot normally get metric neoprene.

engrp
07-08-2012, 10:27 AM
thanks for the advise, ranger1

PaulZ
07-08-2012, 12:49 PM
Hi engrp
There are several things that need to be taken into consideration when selecting the best O ring material, these are rotating or stationary, hot or cold gas, oil.
I have an O ring selection chart put out by Ludowici who manufacture O Rings, when I find it I will post it if it is not to big.
As Ranger said Neoprene and Nitrile are good on NH3, from memory Neoprene is not the best for hot gas in a rotary situation.
Paul

engrp
08-08-2012, 07:49 AM
thanks for the advise,paulZ.

PaulZ
13-08-2012, 03:12 AM
Hi engrp
See this link for the O Ring info.
http://www.sendspace.com/file/0godj3
Paul

Grizzly
13-08-2012, 07:09 AM
Paul.
Well deserved rep points sent. For continuing to uphold the principle of the forum!
Grizzly

Josip
13-08-2012, 03:15 PM
Hi, engrp :)


I am doing rehab works on our grasso rc612. we will be needing a number of o rings. however, the cost of the o ring from the oe supplier is very expensive. there are a number of o ring stores from which , i think i can purchases the o rings, but i don't know the material for the o rings. maybe, some of you who have purchased o rings for grasso recips have an idea. i looked at the compatibility chart of o rings in one website, and it says, either butyl or neoprene is compatible with ammonia. any of you have any advise ? thank you

Maybe, as you said, but will save headache to you ;), believe me .... sometimes very expensive OEM spare parts are very cheap if you have a bad luck and purchase a very cheap one what can be only in that moment ...

All O-rings made of rubber ... "N" nitrile i.e. buna, or special class HNBR (Hydrogenated Nitrile Butadiene Rubber), VITON, EPDM, silicone etc. are more or less resistant to ammonia .... agree with RANGER1 and PaulZ, but for me the biggest problem is resistance to oil ....

Recently, in one engine room with Sabroe piston SMC, screws SAB 202 and Mycom screws all running on mineral oil without any problem ... but someone suggested them to change to some kind of semi sintetic or sintetic oil because that one is much better and no need to change so frequently :eek:, running longer time without any problem ... you know that commercial tricks, cannot use a proper word, sorry;)

....they call us to help when complete engine room were flooded with new type of oil coming out from all interconnection places on SMC compressors with an old type of O-rings ... to make it short they spent almost 2 months to order and replace all leaking O-rings ... I asked them why not request an opinion about oil change before ordering new oil .... long silence ... men in spares purchase department has a friend in company selling oils ....

Here is one good link for online DuPont chemical resistance guide ... you must register before you can use it ... seems good and helpful ..

http://www.dupontelastomers.com/tech_info/chemical.asp

PaulZ, thanks for list.

Best regards, Josip :)

RANGER1
13-08-2012, 08:47 PM
All good information.
I also looked up what Danfoss use.
In the standard range its chloroprene(neoprene), which seem to work OK.
Its maximum working temp is 100 deg C which basically reduces its life on especially Grasso recip discharge valve.
Danfoss in its new range use a teflon spring loaded seal as well as an "0" ring suitable for everything including CO2.
If you never want to replace it again install "Kalrez" elastomer, but of course you have to pay.
They are good for 300 deg C, no shrinkage, no nothing.
Definately recommend silicon "0" ring grease.
Also engrp has to clean up shaft in his case which he knows about.

PaulZ
17-08-2012, 01:42 AM
Thanks Grizz
Only too happy to help as I have received assistance from many on this forum you included.
Paul

engrp
17-08-2012, 01:37 PM
again, thanks josip, paul z and ranger1. with regards to replacing oil on compressors, i also would not dare do it. i have more experience in cars than in ammonia compressors, so i am very conservative,in shifting lubricants in ammonia compressors. and yes, even in internal combustion engines, sometimes you do encounter some weird leaks on valve cover gaskets, spark plug seals and other rubber parts as a result of shifting from conventional mineral oils to synthetic oils.