Reference guide
Seal types: which seal does which job
Seal types sort by what moves at the joint they close. Static seals, such as gaskets and O-rings, close a joint where nothing moves. Rotating shaft seals work where a shaft turns, and reciprocating seals work on a rod or piston that strokes in and out. Parts that fit no standard type are molded or machined to a drawing.
Seal types by what moves
Start with the motion at the joint, because it narrows the choice before size or material comes into it. Each row says what the seal keeps in or out and links the page that covers it.
| Seal type | What moves | What it keeps in or out | Page |
|---|---|---|---|
| Static joints | |||
| Gasket | Nothing: two flat faces bolted together | Fluid or gas in, and dust or weather out, across the whole face of the joint | Gaskets |
| O-ring | Nothing in a static groove; the same ring also seals a moving rod or piston in a dynamic groove | Fluid or gas, sealed by squeezing the ring in its groove | O-rings |
| Rotating shafts | |||
| Radial shaft seal (oil seal) | A turning shaft, under a flexible lip | Oil or grease in, dirt and water out; a standard lip seal is not a pressure seal | Radial shaft seals |
| V-ring axial seal | A turning shaft; the ring turns with it and runs against a face | Dirt out, and liquid flung clear of a bearing or another seal | V-ring axial seals |
| Bearing isolator | A turning shaft, with no rubbing contact on it | Lubricant in and dirt out, with no rubbing lip to wear | Bearing isolators |
| Mechanical seal | A pump or mixer shaft | The pumped or mixed fluid, at the point where the shaft leaves the housing | Mechanical seals |
| Reciprocating rods and pistons | |||
| Piston seal | A piston stroking in its bore | Pressure on one side of the piston, kept from the other; a leak stays inside the cylinder | Piston seals |
| Rod seal | A rod stroking through the cylinder head | Fluid in the cylinder; a leak shows as oil on the rod | Rod seals and wipers |
| Wiper | A rod as it retracts | Dirt, mud and water, scraped off the rod before it goes back in | Rod seals and wipers |
| X-ring | A rod or piston, in place of an O-ring | Fluid, sealed by a ring with four lobes in place of a round section | X-rings |
| V-packing set | A rod or a piston | Fluid, with a stack of V-shaped rings fitted as one set | Hydraulic seals |
| Spring-energized PTFE seal | A rod, a bore or a face | Fluid or gas, sealed by a PTFE jacket that a metal spring keeps pressed against the surface | Spring-energized PTFE seals |
| Made to a drawing | |||
| Custom molded rubber part | Whatever the drawing shows | Whatever the joint needs, where no catalog part fits | Custom molded rubber |
| Rubber-to-metal bonded part | Whatever the drawing shows | Fluid or vibration, with the rubber bonded onto a metal insert | Rubber-to-metal bonded |
| Machined plastic part | Whatever the drawing shows | Fluid, with a rigid ring or seat where a rubber part would not hold its shape | Machined plastic parts |
If the part in front of you matches none of these, send its part number or drawing through the request-a-quote form.
What Conquest Seal supplies and quotes
Each line below says how Conquest Seal handles that type. For the other seal types on this page, send the part number or drawing and we quote it.
- O-rings: we stock every AS568 size, and we quote metric sizes and anything else in the compound your drawing calls for.
- Gaskets: sheet gaskets are waterjet-cut to your print in our own shop in Orange, California, with no die or tooling; felt, mica and tanged graphite are cut by the sheet maker or a cutting partner.
- Radial shaft (oil) seals: single lip, double lip and spring-loaded seals in inch and metric sizes, bought from the manufacturer or its distribution network.
- Hydraulic seals: rod seals, piston seals, symmetrical U-cups, wipers and V-packing sets in polyurethane, nitrile, FKM and PTFE, in inch and metric profiles, from the manufacturers we source from.
- Mechanical seals: Conquest quotes mechanical seals to the part number, the equipment model or the seal drawing.
- Custom molded rubber: made to your drawing by the molders we source from.
- Rubber-to-metal bonded parts, bonded seals included: made to your print by the molders we source from.
- Plastic parts such as seats and bushings: machined to your print by the shops we source from.
Every order ships with a certificate of conformance. Send the part number, the size or the drawing, with the quantity, through the request-a-quote form.
Parker® is a trademark of Parker Hannifin Corporation; NOK® is a trademark of NOK Corporation. No affiliation or endorsement is implied.
Sources
- Parker Fluid Power Seal Design Guide, Catalog EPS 5370/USA, section 1, pages 1-2 to 1-7 (hydraulic seal functions), read 2026-09-25
- Parker Rotary Seal Design Guide, Catalog EPS 5350/USA, section 1 (bearing isolators and V-seals), read 2026-09-17
- NOK Oil Seals catalogue 014E (what an oil seal does), read 2026-09-16
Frequently asked questions
What are the main types of seals?
Seals group by the motion at the joint. Gaskets and O-rings close joints where nothing moves, oil seals and mechanical seals work where a shaft turns, and rod and piston seals work where a rod or piston strokes in and out. A part that fits none of those families is molded or machined to a drawing.
What is the difference between a static and a dynamic seal?
A static seal closes a joint where the two parts do not move against each other, such as a gasket between two flanges. A dynamic seal runs against a moving surface, a turning shaft or a stroking rod or piston, so friction and wear come into the choice as well as the fluid and the temperature. One O-ring can do either job, in a groove cut for that duty.
How do I order a seal when I do not know its type?
Send the part number printed on the seal or listed in the equipment's parts list, or the drawing, and we quote it. If there is neither, say what the seal does in the machine and whether anything moves at the joint, and send the dimensions you can measure.
Related guides
Orders are handled under Conquest Seal's AS9100D quality management system, whose certificate scope includes distribution.
Send the part number and we quote it
Part number or drawing, compound if you know it, and the quantity. A Conquest representative reads every request and replies. Quotes answered within one business day. A person answers (714) 632-9830, Pacific business hours.
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