Page 14: of Marine Technology Magazine (May/Jun 2026)

LANDER LAB #19

O-RING

SEAL DESIGN,

PART 2:

RADIAL SEALS FOR

EXTERNAL PRESSURE

Image courtesy Parker Hanni? n, adapted by the author for this article

By Kevin Hardy, MTR Columnist, President, Global Ocean Design LLC cean engineers are ? rst tasked with keeping the water back-up seal to a primary face seal. Occasionally, two radial on the outside. A breach in the hull can mess-up a good seals are used. The ? rst seal to see pressure is the primary. The

O day at sea. second seal to see pressure, in the event of the failure of the

Our discussion of o-ring seal design began with a look at primary, is the secondary.

Face Seals in the Marine Technology Reporter, Jan/Feb 2026, O-ring stretch: If the ideal design groove is in between two pp. 20-23. o-ring sizes, you can stretch the smaller o-ring to ? t the larger

There is important background and basics in that article that groove. You can make a smaller o-ring larger, but you cannot relate just as much to this article, but not fully repeated here. make a larger o-ring smaller. When an o-ring is stretched on

To summarize those basics: installation in the groove, the cross-section is ? attened. Be- 1. There is no better design reference for o-ring seal design yond 2-3% of stretch, the groove depth must be reduced to than the Parker O-ring Handbook (ORD-5700). A pdf is avail- retain the necessary squeeze. Parker recommends not stretch- able to download for free (See “Citations” below). It is man- ing the o-ring over 5% as that reduces life. (Ref: Parker ORD datory reading for ocean engineers, and contains much more 5700, Section 3.5, “Stretch”). detail than possible in any article. The temporary ID expansion to reach the groove during as- 2. The o-ring seal creates a barrier to ? uid ? ow. The o-ring sembly typically does not exceed 25-50%.

seal assembly consists of an o-ring captured in a groove. Durometer: A higher durometer o-ring resists extrusion bet- 3. Assembly lubricants should always be used sparingly. ter. A lower durometer o-rings are more tolerant of surface im-

They are used to decrease friction and allow the o-ring to re- perfections. Using a 70-durometer o-ring with a 90-durometer spond to pressure and move inside the groove. back-up ring provides the best of both.

4. The leading cause of o-ring failure is extrusion through Outside groove versus Inside groove: An o-ring groove on a gap. the OD of a plug is considered a “Male” groove. They are 5. A Radial seal requires a gap to assist with assembly that much easier to machine, anodize, clean, assemble, and in- the Face seal design does not. spect. A groove on the inside of a mating end cap is consid-

A Radial seal is chosen when: 1) there is limited ? ange area ered a “Female” groove. These are seen much less frequently.

for a face seal and endcap retaining bolts, or 2) as a secondary

Figure 1 (above)

An o-ring is shown in a radial groove with the endcap secured. Note the use of a back-up ring and lead-in chamfers. 14 May/June2026

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