Fluid compatibility
The wrong seal material in the right size still leaks. A seal that is incompatible with the fluid swells, hardens or dissolves, and it does it in weeks rather than years. Check the fluid before you pick a material.
The four that cover most machines
Petroleum hydraulic oil
Nitrile, or polyurethane for the dynamic seals
The default on almost every machine. Nitrile handles mineral oil to about 240°F and costs the least; polyurethane wears far better on a rod.
Phosphate ester (Skydrol, Fyrquel, Houghto-Safe 1000 series)
EPDM
Fire-resistant fluids destroy nitrile and polyurethane. EPDM seals them; it is the one case where the usual choice is exactly wrong.
Water-glycol fire-resistant fluid
Nitrile
Nitrile is fine. Polyurethane hydrolyses in water-based fluids and will go soft and sticky.
Hot oil, above 250°F, or biodiesel
Fluorocarbon (Viton)
Costs several times nitrile and it is worth it. Nitrile hardens and cracks; the kit fails again in a season.
Look up a fluid
Ratings run 1 to 4. 1 is satisfactory, 2 and 3 mean it will hold a static joint but not a moving rod, 4 means it will not work, and X means we have no rating for it.
983 fluids listed. Type a few letters to narrow it down.
Rating scale
- 1
- Satisfactory
- 2
- Fair — usually OK for a static seal
- 3
- Doubtful — sometimes OK for a static seal
- 4
- Unsatisfactory
- X
- No data
Materials covered
Fourteen materials are rated for every fluid. We stock the first four as standard; the rest we order in.
- Nitrile (Buna-N)
- Ethylene propylene (EPDM)
- Fluorocarbon (Viton/FKM)
- Neoprene
- SBR
- Polyacrylate
- Polyurethane
- Butyl
- Butadiene
- Isoprene
- Natural rubber
- Hypalon
- Fluorosilicone
- Silicone