Basic Knowledge of Seals - Classification of Hydraulic Dynamic Seals

Sealing elements have a decisive influence on the design, functionality, and service life of hydraulic systems. Hydraulic seals are typically made from various materials such as rubber, polytetrafluoroethylene (PTFE), and polyurethane (PU). The choice of material depends on specific operating media or limitations due to pressure, fluid type, temperature, or chemical compatibility. Hydraulic static seals are located within the cylinder body without movement. Hydraulic dynamic seals are usually piston seals and rod seals. Rod seals are installed in the grooves of hydraulic cylinders, with their inner diameter moving relative to the piston rod or shaft; while piston seals are installed in the grooves of pistons, with their outer diameter moving relative to the cylinder bore or housing. Therefore, rod seals are commonly known as shaft seals, while piston seals are also called bore seals.

How many types of hydraulic dynamic seals are there?

Hydraulic dynamic seals can be divided into five major categories based on their functions. These are piston seals, rod seals, dust seals, rotary seals, and wear rings (guide rings)

1. Piston Seals

The function of piston seals is to ensure that the liquid working medium in the hydraulic cylinder does not leak through the piston head. Piston seals typically include single-direction seals and double-direction seals. Single-direction seals mean pressure only acts in one direction, while double-direction seals allow pressure to act in both directions of reciprocating motion.

2. Rod Seals

3. Dust Seals

Dust seals, in addition to their cylinder sealing function, primarily serve to prevent external contaminants such as dust and dirt from entering the cylinder. Dust seals are typically used in conjunction with other sealing components to create a tight fit while still allowing the piston to move linearly back and forth.

4. Rotary Seals

Rotary seals are bidirectional sealing rings that can withstand pressure from both sides or alternating pressure. They are used to seal components such as rods, shafts, pins, and rotary joints that undergo rotational or oscillating movements.

5. Wear Rings

Wear rings used in hydraulic cylinders can effectively maintain piston concentration, evenly distribute wear generated during cylinder reciprocating motion, and apply stress distribution on sealing elements. The installation of piston rods and pistons typically requires the use of wear rings.