The specific function of the sealing element

Core function: Four "precautions" 

First, leak prevention - this is the most fundamental function. 

For any two components that fit together, there will always be a certain gap at the microscopic level. No matter how well they fit, there will always be some space. The sealing piece uses its own elastic deformation to fill this gap, preventing liquids, gases, oil, and steam from escaping. If the oil seal in the hydraulic cylinder leaks, the entire system will lose pressure; if the gasket on the pipe flange leaks, the medium will spray out. The sealing piece is like the "rubber mud" stuck in these gaps, but it is a thousand times more reliable than rubber mud. 

Second, prevention of intrusion - keeping the outside dirt and contaminants out. 

Not only is it necessary to prevent things from going out, but also to prevent things from entering from the outside. Dust, sand, water, corrosive gases - once they enter the precision mating surfaces, they will accelerate wear and even cause the parts to get stuck. For example, the oil seal of the engine crankshaft - on the one hand, it prevents the engine oil from leaking out, and on the other hand, it prevents dirt and water from entering. The dust-proof sealing ring is exactly for this purpose. 

Third, prevent cross-contamination and leakage - separate the two different media. 

In many devices, there are two or more types of media present simultaneously. For instance, hot water and cold water cannot be mixed, oil and water cannot be mixed, and the high-pressure side and the low-pressure side cannot be connected. The function of the sealing element here is to act as an "isolation barrier". The gaskets in the heat exchanger are used to prevent the exchange of hot and cold fluids; the piston seals in the double-acting cylinder are used to prevent the gases in the left and right chambers from communicating with each other. 

Fourth, prevent pressure loss - maintain pressure. 

The hydraulic system, pneumatic system, and refrigeration system all operate based on pressure differences. Once the sealing components fail, pressure will slowly leak out, causing the system efficiency to plummet sharply and even leading to total paralysis. A few dollars' worth of an O-ring can potentially ensure the normal operation of tens of thousands of pieces of equipment. 

Extended function: Not just "blocking" 

Buffering and shock absorption. 

The seals are usually made of elastic materials (such as rubber, silicone, polyurethane, etc.) and have the ability to deform. During the reciprocating motion of the piston, the seals can absorb some of the impact and vibration, reducing the hard contact between the metal parts and prolonging the lifespan of the components. The seals in the hydraulic cylinder are also "shock absorbers". 

Compensate for wear and tear. 

Over time, the parts will wear out and the clearance between them will increase. The elastic sealing element can automatically compensate for this gap - if it wears a little, it will deform a little and continue to fit tightly. That's why rubber seals are more durable than metal gaskets because they can "adapt". 

Direction and positioning. 

Some sealing components not only perform the sealing function but also serve as a guiding role. For instance, the guiding ring on the piston rod not only prevents oil leakage but also ensures that the piston rod does not wear unevenly, keeping the movement trajectory centered. 

Transmitting force. 

In hydraulic and pneumatic systems, seals not only serve as passive leak-proofing components, but also act as the medium for force transmission. The seals on the piston of the oil cylinder convert the oil pressure into thrust. If the load cannot be pushed, the seals are also responsible. 

Based on the application scenarios, the specific functions can be identified. 

Engine field: The front and rear oil seals of the crankshaft prevent oil from leaking out, the valve oil seals prevent oil from flowing into the combustion chamber (otherwise, oil will be burned), and the cylinder gasket prevents high-pressure gas in the cylinder from leaking into the water passage or oil passage. Any failure of these components will result in minor smoke emissions or severe cases such as cylinder seizure and equipment scrapping. 

Pipe flange: The function of the gasket is to form a sealing surface between the two flanges, to bear the preload force of the bolts, and to resist internal pressure and temperature fluctuations. If the gasket is wrongly selected (in terms of material, thickness, or form), the flange will leak. 

Hydraulic and pneumatic system: This is the scenario with the largest usage of seals. There are piston seals, rod seals, dust rings in the hydraulic cylinder, shaft seals in the hydraulic pump, and O-rings and combined gaskets in the valve body. A hydraulic system has at least a dozen sealing points and can have hundreds of them. Any leakage will cause the system to fail. 

Household appliances: The door seal of the washing machine prevents water from leaking out. The sealing ring of the rice cooker ensures pressure cooking. The nuts of the air conditioner connection pipes have sealing gaskets to prevent refrigerant leakage. 

Chemical Engineering and Pharmaceuticals: The diaphragm in the diaphragm valve, and the gasket of the manhole in the reaction vessel, must not only be able to seal but also be resistant to corrosion and high temperatures, and must not contaminate the medium. The role of these sealing components has been elevated to the "safety + cleanliness" level. 

How serious are the consequences of a sealing component failure? 

Light: Slow leakage, waste of medium, increase in operation and maintenance costs. 

Medium level: Insufficient system pressure, decreased equipment efficiency, and substandard products. 

Serious: High-temperature and high-pressure media jetting (steam, gas, hydraulic oil) can cause burns, fires and explosions. The root cause of many industrial accidents in history was the aging and failure of a sealing component. 

So although the cost of the sealing components may only be a few cents to several dollars, they protect the safety and operation of the entire system.