Orings  Characteristics

Orings characteristics continued:

C. A single oring will seal with pressure applied alternately on one side and then on the other, but in cases of severe loading or usage under necessarily unfavorable conditions, seal life can be extended by designing the mechanism so that each seal is subjected to pressure in one direction only. Seals may be arranged in series as a safety measure but the first seal exposed to pressure will take full load.

D. Oring seals must be radially compressed between the bottom of the seal groove and the cylinder wall for proper sealing action. This compression may cause the seal to roll slightly in its groove under certain conditions of piston motion, but the rolling action is not necessary for normal operation of the seals.


E. In either static or moving O-ring seal under high pressure the primary cause of seal failure is extrusion of the seal material into the piston-cylinder clearance. The major factors affecting extrusion are fluid pressure, seal hardness and strength, and piston-cylinder clearance.


F. Moving seals may fail by abrasion against the cylinder or piston walls. Therefore, the contacting surfaces should be highly polished for long seal life. Moving seals that pass over ports or surface irregularities while under hydraulic pressure are very quickly cut or worn to failure.

*Excerpt taken from:  "O-Ring Seals in the Design of Hydraulic Mechanisms" A paper presented at the S.A.A. Annual Meeting,January, 1947 by Mr. D.R. Pearl of Ha,. Std. Prop. Div. of United Aircraft Corp.