Yes, you can touch a mechanical seal, but keep your fingers off its two sealing faces, the lapped surfaces where the primary ring runs against the mating ring, one of them turning with the shaft.
Which Parts of a Mechanical Seal You Can Touch
Everything on a mechanical seal except the two lapped faces can be handled: the gland, sleeve, springs or bellows, drive collar, set screws, and the O-rings and other rubber parts. Pick up a loose primary ring or mating ring by its outside edge so that nothing touches the polished face.
When you lubricate the O-rings and rubber bellows during fitting, keep the lubricant to a light film and keep it away from the faces.
On a component seal, where the seat and the rotating head are fitted as separate pieces, press the mating ring into its bore through a clean, soft spacer, such as the cardboard washer some seals are packed with, so that no tool or thumb bears on the lapped surface.
On a cartridge seal, the faces come preassembled inside the unit. Handle a cartridge by its gland and sleeve, and do not take it apart to look at the faces.
Why Touching the Seal Faces Causes Leaks
Touching a seal face causes leaks because a fingerprint leaves oil and dirt on a surface that seals only because it is extremely flat and runs extremely close to its mating face. The running gap between the two faces of a mechanical seal varies from about 5 to 50 microinches (about 0.13 to 1.3 µm) or more, and whatever a finger leaves on a face ends up in that gap.
Oil on a face changes how the two faces meet, and a grit particle holds them apart or scratches the lapped finish once the shaft turns. Leakage across the faces rises with the cube of the gap between them.
Gloves or Clean Hands
Gloves and clean hands both work, as long as whatever touches the seal is clean and lint-free; the instruction sheet that comes with the seal settles which.
Before you install a new seal, leave it in its unopened box until you need it, and lay the parts out on a clean work surface rather than on the pump base.
Can a Touched Seal Face Still Be Used
Yes. A fingerprint on a new seal face comes off: wipe the face clean with isopropyl alcohol or another quick-drying solvent on a lint-free cloth just before fitting, then keep your fingers off it.
Scratches and chips are what rule a face out, because they are damage to the lapped surface that no solvent removes. Check the face for them under good light before fitting.
Touching a Running Seal
No, keep your hands off a mechanical seal while the pump is running. The drive collar, set screws and sleeve turn with the shaft and can catch a glove, a cuff or a finger, so those parts belong behind a guard.
The outside of the seal also runs at the temperature of the pumped fluid or the barrier fluid, which on hot service is enough to burn. To find out whether a seal is running hot, measure the gland with an infrared thermometer instead of feeling it.