GLAND WORKS

Identifying seals

A seal has no part number on it. What it has is a profile and three measurements, and that is enough to identify it. Work through the family you are holding, write the numbers down, and send them to us — a complete set of seal dimensions identifies a kit more often than a machine model does.

Before you measure

  • Lay the seals out in the order they came off and photograph them next to a rule. Order tells us which is the rod seal and which is the buffer.
  • Measure with a caliper, not a tape. These numbers matter to a few thousandths of an inch.
  • Measure the old seal and the metal it came out of where you can. A seal that has been in service is not the size it was made.
  • Note whether the machine is inch or metric. 50 mm reads 1.968 in, which is close enough to 2 in to send the wrong kit.

Rod seals

Measure

  1. Inside diameter (this is the rod size)
  2. Outside diameter
  3. Height of the seal

Profile

Twin lip
— Two sealing edges pointing inboard.
Single lip
— One sealing edge.
Loaded
— A spring or O-ring sits in the U, pushing the lips apart.
Unloaded
— Nothing in the U — it relies on system pressure alone.

Wipers

Measure

  1. Inside diameter (the rod size)
  2. Outside diameter
  3. Shoulder height
  4. Overall height

Profile

D
— Solid bottom, snaps into a groove.
AN
— Like a D but a thinner section and lower base.
H
— A U-cup on the bottom as well as a wiping lip.
K
— Snap-in, with a distinct retaining shoulder.
MC
— Metal-cased — a steel shell with a rubber or urethane lip.

Piston seals

Measure

  1. Bore size
  2. Groove width
  3. Groove diameter

Profile

One-piece U-cup
— A single moulded seal.
Two-piece
— A PTFE or urethane cap over a rubber energiser.
Three or more pieces
— Cap, energiser and one or two anti-extrusion rings.
T-seal
— A T-shaped section with a back-up ring either side.

Note anything unusual: a quad ring on the outside diameter, or a seal that looks like two pieces but is moulded as one. Count the pieces and measure the inside diameter of the main seal.

Wear rings and bearings

Measure

  1. Outside diameter
  2. Cross-section
  3. Width

Profile

Split
— Cut across so it can be sprung into the groove.
Solid
— Continuous ring, fitted over the end.

Reading a failed seal

The seal that came out tells you what killed it. That matters, because most of these will kill the new one too. Find the row that matches what you are holding.

Hardened, glazed, cracked

Looks like:
The dynamic face is hard and shiny, with fine cracks across it.
Cause:
Heat. Either the fluid runs too hot or the stroke speed is high.
Fix:
Lower the oil temperature or slow the stroke. If neither can change, move to a fluorocarbon seal.

Worn to a mirror finish

Looks like:
The dynamic face is polished smooth and the seal is undersize.
Cause:
Not enough lubrication.
Fix:
Check oil viscosity and level. Consider a seal profile that carries a lubricating film.

Worn egg-shaped, or worn on one side only

Looks like:
The bore of the seal is oval, or one side of the lip is gone and the other is untouched.
Cause:
The rod or bore is not concentric, or the wear ring is gone and the piston is riding on the seal.
Fix:
Replace the wear rings and check the rod for bending. New seals alone will fail the same way.

Cut or dented lip

Looks like:
A clean nick in the sealing edge, often a single one.
Cause:
Damage during installation, or storage on a nail or a peg.
Fix:
Use an installation tool, tape over snap-ring grooves and keyways, and store seals flat in a closed box.

Scratched along the dynamic face

Looks like:
Fine scoring running around the seal.
Cause:
Scoring on the rod or bore, or grit in the fluid.
Fix:
Hone or polish the metal, flush the system and check the wiper — the wiper is what was supposed to stop this.

Soft, swollen, misshapen

Looks like:
The seal is larger than the new one and will not go back into its groove.
Cause:
The fluid and the seal material are incompatible, or water has got into the system.
Fix:
Change compound or fluid. Check the fluid against the material before ordering again.

Crumbling, cracked all over

Looks like:
The material breaks up when handled.
Cause:
High fluid temperature, or exposure to ozone, sunlight or arc welding.
Fix:
Store seals away from sunlight and welding, and lower the oil temperature.

Axial cuts, grooves along the stroke

Looks like:
Cuts running the same way the seal moves.
Cause:
Metal chips or other debris in the system, or imploded air bubbles.
Fix:
Flush the system and bleed the air out.

Extruded — material pushed out of the groove

Looks like:
A thin skirt of material squeezed out on one side, usually the low-pressure side.
Cause:
The clearance gap is too wide, the bearings are worn, or the pressure is above what the seal is rated for.
Fix:
Fit a back-up ring, replace the wear rings, or move to a harder compound.

Send us the numbers

If you have the profile and the measurements and still cannot find the kit, send them over with a photo. Include the bore, the rod, the seal dimensions and what the machine is. We will tell you what fits, or that we cannot get it.

See also: measuring the cylinder and gland and groove dimensions.