Synthetic Oil and O-ring seals

[tomrscott]

I was reading through the applications information in the Weatherhead catalog (one of the larger makers of hydraulic fittings - see links below) and came across this warning. Just curious if it applies to the synthetic oils we've talked about, or are they unrelated?

"Petroleum or Mineral Oil Based Hydraulic Fluids - ... good general purpose fluids ... All Weatherhead fittings and O-rings can be used with these fluids."

"Straight Synthetic Hydraulic Fluids - is a general term applied to such products as Pydraul, Lindol, Cellulubes 90, 150, 180, 220, etc. ... O-rings must be made of "Butyl" compound or they will "swell" when contacted by synthetic fluids."

This latter note clearly excludes the "Buna-N" O-ring material that is in almost all of Weatherhead's fittings, and I believe is the standard material.

If this note applied to the synthetic engine and transmission oils so popular with many, and often used in our hydraulic systems, there would be a real concern with O-ring hydraulic fittings, quick disconnects, and other applications. I believe most of these use Buna-N O-rings.

Are the synthetic engine oils different from the synthetics they are talking about, or should this be a concern? /forums/images/graemlins/ooo.gif

Link to Eaton Weatherhead catalogs online:
http://hydraulics.eaton.com/products/hose_and_fittings_main.htm#wh202

Link to Steel Fittings section that talks about O-Rings and synthetics:
http://hydraulics.eaton.com/products/pdfs/W-HYOV-MC001-E_steel_fittings.pdf

 

[Youare]

Buna-N also known as Nitrile rubber is a good choice in
O-rings for most petroleum based fluids. Viton is also an
O-ring material that performs well but is more expensive.

Butyl has a little better solvent resistance than Nitrile which is probably why that material is recommened. Depending on where and what the O-ring is sealing would give an indication of failure rates.

If the O-ring is on a fitting as a face seal or a quick disconnect a little swelling would not hurt the seal, if the fluid started to disolve the elastomer that would be another issue. In these applications the fluid to seal contact is not that great

In a spool valve where there is movement swelling could make the valve sticky and the O-ring wear away faster as the edges of the spool move on the O-ring.

For the best service go with what the maunfacturer of the fluid recommends. Weatherhead makes fittings so they don't want to see a failure because of the wrong elastomer and fluid combinations.

Temperature is another factor to consider.

Randy