Neoprene vs nitrile

[zoidberg]

The conventional wisdom is to use neoprene impellers when pumping water, and nitrile when pumping oil-based fluid.... for components of oil-based stuff attacks/degrades the neoprene kit.

A skilled/experienced diesel mech in Newlyn advised us always to use nitrile impellers ( after a complex failure ), for many boats sit in diesel scum-rich marina berths, where the intake sucks such degrading stuff into the strainer and then into the impeller chamber, where it can sit undisturbed for weeks after the engine is shut down. Time after time....

According to him, that contributes to the failure of many neoprene impellers.

Views? Experiences? Prejudices?

 

[earlybird]

Johnson seem to have replaced neoprene by MC97, whatever that is, claiming better life. This is what ASAP supply for the pump on my Beta.
The one I purchased has lasted longer than the original impeller, but I don't know what that was.

 

[thinwater]

Neoprene is also attacked by propylene glycol (non-toxic antifreeze). It makes it stiff and the vanes become more prone to cracking. Nitrile is not. Also an issue in heads, where some have neoprene internals an some have nitrile.

Neither is attacked by ethylene glycol.

 

[vyv_cox]

You may find this reference table useful http://www.quickcutgasket.com/pdf/Chemical-Resistance-Chart.pdf This rates nitrile as 'A' (no effect - excellent) in mineral oil and neoprene 'B' (minor effect, good). Interestingly, both are rated the same, A and B, in fresh and salt water although it does not give a concentration for the latter.

This table http://www.marcorubber.com/materialguide.htm also rates neoprene somewhat lower in oil than nitrile and, somewhat oddly, recommends nitrile for water but does not mention it for neoprene.

It has always been my understanding that neoprene was OK for oil contaminated water and I know that several diaphragms in bilge pumps are made from it, but these two tables seem to say that nitrile is the preference almost always.

 

[lw395]

In my experience the unreliability of impellers is much overstated.
So long as there is a spare on board, they almost never fail!

 

[Deleted member 36384]

.... So long as there is a spare on board, they almost never fail!

The opposite of course being completely true.

 

[earlybird]

According to this website, neoprene has the slightly better low temperature performance, but there's not much in the way of data.
http://www.pumpagents.com/JabscoPumps/Jabsco-Impeller-Guide.html

 

[zoidberg]

I notice that some impeller replacements come with a tiny tube of lubricant grease in the bubble pack - and, of course, that adds to the considerable cost.

What does the team think are appropriate alternative lubricant greases for salt-water impellers - and which are not?

Margarine or Lurpak? McLube or KY?

 

[alahol2]

What does the team think are appropriate alternative lubricant greases for salt-water impellers - and which are not?

I've always used a smear of silicone grease, it's fairly inert and definitely safe on all rubber/neoprene/nitrile etc.