Before assembly
- Check the part number, material and lot against the drawing.
- Inspect the seal for cuts, flash, contamination.
- Clean the groove, shaft and bore. Remove burrs, swarf, paint and old seal.
- Check lead-in chamfers (15 to 20 degrees) and groove corners.
Lubricants
Use a lubricant that is compatible with both the seal and the system fluid.
| Seal material | Avoid | Typical lubricants |
|---|---|---|
| NBR, HNBR | Silicone grease can be fine, check swelling in oils | Mineral oil, light grease |
| EPDM | Mineral oil, petroleum grease (they swell EPDM) | Silicone grease, glycerine-based |
| Silicone | Silicone grease | Fluorinated or glycerine grease |
| FKM | Ketones, amines | Silicone or fluorinated grease |
| FFKM, PTFE | None specific | Fluorinated grease |
Use a thin film. Too much grease can cause hydraulic lock or contaminate the product.
Fitting
- Do not roll the ring over the shaft; roll creates twists.
- Avoid stretching beyond 50 percent for installation; shorter lengths of cord recover.
- Use installation sleeves or cones to carry the ring over threads, splines and keyways.
- Use picks made of plastic or brass, not steel.
- Seat the ring evenly in the groove, with no twist. A line moulded on the ring (parting line) should not spiral.
- Insert pistons or rods with a straight, slow movement, not a twisting push.
- For split grooves or PTFE seals, follow the maker's tool and heating instructions.
Common errors
- Pinching during closing the cover.
- Re-using an old O-ring.
- Wrong size from a mixed assortment kit.
- Dirt on the ring.
- Over-lubricating or using the wrong grease.
- Sharp edges on threads.
Tightening
Tighten covers evenly in a star pattern. Metal-to-metal contact (where designed) sets the squeeze. Do not over-torque a face seal to compensate for a leak.
Records
For critical assemblies record the seal lot, who installed it and the torque. That makes later failure investigation possible.
About this article. It is original writing prepared from public sources, standards and general industry practice. It is not a copy of any book or standard and it is not engineering advice. Confirm values against the current edition of the standard and test in your own application. Only analyse material you own or are entitled to analyse.
