Scrapers
Rod seals
Piston Seals
Guide rings
Back-Up rings
O-Rings / X-Rings
Flat seals
Spring-loaded seals
Radial shaft seals
Rotary seals
High pressure seals
Sealing sets
O-ring measuring towers
Turned parts
Milled parts
Turned and milled parts
Bushes or bearings
Large format 3D printing
Post-processing of 3D printed parts
Heat-resistant 3D printed components
Plastic Components with Flame Retardancy
Static Seals
Definition and Distinction
Static seals are seals that seal two components against each other without relative motion in operation. Their purpose is clear: they prevent the escape or ingress of media such as water, oil, air, or gases. The sealing effect arises because the seal is compressed during joining and thereby adapts elastically (recovering) and partly plastically (permanently) to the sealing surfaces. As a result, microscopic unevenness is bridged that would otherwise form leak paths.
In contrast, dynamic seals work at points with motion, for example at shafts or piston rods. There, friction and the resulting wear additionally come on as dominant loads. Static seals are therefore often longer-lived, yet they are not uncritical in design, because contact pressure, geometry, and surface strongly influence tightness.
What Does “Static” Mean in Sealing Technology?
“Static” means in sealing technology that the sealing partners do not slide or rotate against each other in operation. The connection is usually bolted, pressed, clamped, or bonded. Frequent examples are housing-cover connections, flange connections, or closure screws with a sealing element.
Nevertheless, motion plays an indirect role, because the necessary deformation only arises during installation through the tightening of bolts or the joining of the parts. In particular, flatness, edges, and lead-in chamfers often decide whether the seal reaches its final position undamaged.
Designs and Typical Applications
In practice, few designs dominate because they cover many standard cases. O-rings, flat seals, and profile seals are found in mechanical engineering, fluid technology, valves and fittings, housings, and piping. Which seal is suitable usually depends on three questions: where the sealing point is located — flange, groove, or cover — which medium shall stay tight (chemical resistance), and which operating conditions act — pressure, temperature, and installation forces.
| Design | Typical sealing point | Strengths | Typical media / notes |
|---|---|---|---|
| O-ring | Groove, axial or radial | Compact, well standardized | Liquids and gases; material must match chemically |
| Flat seal / gasket | Flange, cover, housing joint | Large surfaces, good with simple geometries | Often water, oil, or process media; pressure distribution important |
| Profile seal | Defined geometry, e.g., frame | Good adaptation, sealing lips possible | Housing sealing, IP protection; installation guidance important |
O-Ring (Static Axial and Radial)
The O-ring is a ring-shaped elastomer seal that sits in a groove, also called installation space or gland. During assembly, it is deliberately compressed. This compression is often referred to in design as squeeze and describes the percentage compression of the cross-section.
With statically axial installation, the O-ring seals between two end faces — for example between cover and housing or at a flange. With statically radial installation, it seals between cylinder and bore, that is, via a radial contact. Both variants use the same principle but differ in the geometry of the groove and in the way installation forces and tolerances act on the compression.
How Does the Sealing Effect Arise? Important Design Parameters
A static seal works when it generates sufficient contact pressure at the sealing point. Contact pressure is the pressure on the contact surface that arises from bolt force or joining forces. It must be high enough so that the seal fills the micro-roughness of the sealing surfaces and thereby interrupts the leak paths. At the same time, the pressure must not become so high that the seal is damaged or sets too strongly over time.
With elastomers, the compression set is additionally important. It describes how much of the deformation remains permanent after unloading. A high compression set reduces recovery and thereby the sealing reserve, particularly under continuous load and at higher temperature. Operating pressure can additionally support the sealing effect, because it presses the seal against the sealing surface, yet it can also intensify damage mechanisms such as extrusion.
Contact Pressure, Roughness, and Sealing Surfaces
Leakages frequently arise not because too little sealing material is present, but because contact pressure is locally insufficient or sealing surfaces deviate too strongly. Roughness creates microscopic channels that are only closed through deformation of the seal. Therefore, flatness, stiffness of the joining partners, and a uniform bolt force are decisive.
When bolts are tightened unevenly or the flange yields, contact pressure distributes unevenly. Then zones with too low pressure arise, in which media escape first. This is often more critical with gases than with liquids, because gases can already flow through very small leak gaps.
Groove Geometry with Elastomer Seals: Squeeze and Fill Ratio
With O-rings, the groove geometry decides on tightness and service life. Two terms appear quickly here:
- Squeeze (compression): percentage compression of the O-ring cross-section in the installed state. Too little squeeze increases the leakage risk, too much squeeze promotes installation damage and increases compression set.
- Fill ratio: volume share of the O-ring relative to the groove volume. It should not reach , so that space remains for deformation, manufacturing tolerances, and thermal expansion.
In design, a range is therefore usually targeted in which the seal sits reliably without being trapped excessively. This balance is particularly important when temperature and pressure vary strongly.
Installation and Failure Patterns: Causes of Leakage and Damage Mechanisms
In practice, it often becomes clear: static seals are low-friction in operation, yet installation and design decide on success. Frequent causes of leakage are an unsuitable material choice, a groove geometry outside sensible tolerances, damaged sealing edges, or poor pressure distribution through wrong bolt forces. Excessive gap dimensions can also become a problem when pressure pushes the sealing material into the gap.
Typical failure patterns can usually be assigned to a few mechanisms:
| Failure pattern | What happens? | Frequent causes | Basic principle of remedy |
|---|---|---|---|
| Leakage despite new seal | Micro leak paths remain open | Too low or uneven contact pressure, surface defects | Improve contact pressure and flatness, check surface |
| Permanent deformation (set) | Seal does not recover | High compression set, temperature, over-squeeze | Adapt material, reduce squeeze, consider temperature |
| Extrusion | Material is pressed into gap | High pressure + too large gap dimension | Reduce gap, harder material, support element |
Extrusion and Gap Issues Under Pressure Loading
Extrusion means that the seal is pressed under pressure into an existing gap. This happens particularly with elastomers when pressure is high and the gap dimension between the components is too large. The material can then shear or tear, whereby the sealing function is lost abruptly or deteriorates gradually.
In design, three levers help: a controlled, small gap dimension, a suitable, often harder, material, and if needed support elements such as back-up rings that cover the gap. Which combination is sensible depends on pressure level, temperature, and installation conditions.
A short note: at high pressures, gas sealing, or strong temperature changes, a specialized design and material choice is often sensible, because small geometry and material effects influence tightness noticeably.
