Seals And Gaskets Are Maintenance Items With A Clock

A seal is the cheapest component in most products and frequently the one whose failure ends them. It is also a material with a shelf life independent of how much the product is used.

A seal works by being squashed

Sealing depends on a compliant material being compressed between two rigid faces, filling the microscopic gaps that machining leaves behind.

The pressure holding it there comes from the elasticity of the rubber itself. If the material stops pushing back, the seal stops sealing.

This is why a gasket that looks intact can still leak. Appearance says nothing about whether the material has retained its springiness.

Elastomers harden with time and heat

Rubber compounds continue to cure slowly after manufacture. Chains of molecules keep cross-linking, and the material gradually becomes harder and less able to recover its shape.

Heat accelerates this dramatically, so a seal near a motor, a heating element or a hot exhaust ages years faster than an identical one elsewhere in the same product.

The result is compression set: the seal takes on the shape it was held in and no longer springs back when the joint is opened and closed.

Chemistry matters as much as age

Different rubbers resist different things. A compound that shrugs off hot water may swell in oil, and one that resists oil may crack in sunlight.

Cleaning products are the common cause of chemical attack, because a solvent or strong alkali applied to a door seal reaches it far more often than the product's contents do.

Swelling is as damaging as shrinkage. A seal that has grown no longer sits in its groove and gets pinched or extruded the next time the joint closes.

The damage shows up somewhere else

Seals rarely fail loudly. Water that gets past one ends up in a bearing, a board or an insulating layer, and that component is blamed instead.

Air seals behave the same way: a door that no longer closes tightly makes the machine run longer, and the higher running time is read as inefficiency.

Because the symptom appears at a distance from the cause, the repair frequently replaces the expensive part while leaving the failed seal in place.

Handling and storage set the pace

A seal stretched over an edge during assembly acquires a weak point, and it will fail there whatever else happens to the product.

Leaving a door or lid clamped shut for long periods holds the seal compressed continuously, which is the condition that produces compression set fastest.

Storage with the door propped slightly open costs nothing and preserves the one component that determines whether the product still works when it comes out.