Spiral Failure - O-Ring & Engineered Seals Division | Parker US

Failure Modes


SPIRAL FAILURE


Spiral failure of an O-ring is often found on long stroke hydraulic piston seals and to a lesser degree on rod seals. This type of O-ring failure is caused when the seal becomes “hung-up’’ at one point on its diameter (against the cylinder wall) and slides and rolls at the same time. The resultant twisting of the O-ring as the sealed device is cycled finally causes the seal to develop a series of deep spiral cuts (usually at a 45° angle) on the surface of the seal.

Some conditions which cause an O-ring to slide and roll at the same time may be:

  • Eccentric components.
  • Wide clearance combined with side loads.
  • Uneven surface fi nishes.
  • Inadequate or improper lubrication.
  • O-ring too soft.
  • Stroke speed (usually too slow).
  • Improper installation (O-ring pinched or rolled).
  • O-ring sizes outside of recommended dimensions for reciprocating pistons (See chart below):

Gland Dimensions for Industrial Reciprocating O-Ring Seals
Groove Diameter (Rod Gland) Tolerance Groove Diameter (Piston) Tolerance
-.000 for all sizes +.000 for all sizes
+.002 for sizes 2-006 through 2-324 -.002 for sizes 2-006 through 2-324
+.004 for sizes 2-325 through 2-460 -.004 for sizes 2-325 through 2-460



S
ome solutions for spiral failure include
:

  1. Improve surface finish of sealed assembly at dynamic interface (Cylinder Bore, Piston Rod).
  2. Check for out-of-round components (Cylinder Bores especially).
  3. Provide proper lubrication. Consider the use of internally lubed O-rings.
  4. Replace with a harder O-ring.
  5. Consider use of alternate seal shapes. for example, the Parker T-Seal is specifically designed to prevent spiral failure and its use will allow for increased tolerances because of built-in anti-extrusion back-up rings. Parker T-Seals are available to fit a number of standard AS568 O-ring grooves and may directly interchange with O-rings in most cases. Parker Double Chamfered Precision Cut Seal or can be a replacement for an O-ring and back-up assembly.