HIGH TEMPERATURE SEAL

A rod seal is typically seated in a groove (the gland) within the cylinder head. It exerts a specific amount of radial force against the moving rod. In high-temperature scenarios, the seal must manage two competing physical realities:

1. Thermal Expansion: The seal material expands significantly more than the metal housing.
2. Softening: Most polymers lose structural integrity as they heat up, which can lead to "extrusion" (the seal being squeezed into the tiny gaps between the rod and the housing).

Types of High-Temperature Rod Seal Profiles

1. PTFE Cap Seals: A PTFE ring sits on the rod, backed by a high-temp elastomer O-ring. The O-ring provides the "spring," while the PTFE handles the heat and friction.

2. V-Packing (Chevron): Often made of reinforced FKM or PTFE, these stacks are excellent for heavy-duty applications where you can adjust the gland nut to maintain a seal as the material wears.

3. Metal-Energized Seals: For the most extreme cases (vacuum or ultra-high heat), a "C-ring" or "E-ring" made of metal may be used, though these are less common in standard reciprocating hydraulics.

4. Wear Ring

5. D Seal / Step Seal

6. Wiper Seal 

7. Piston U Cup / Rod U Cup Seal 

The primary benefit of high-temperature rod seals isn't just "withstanding heat"—it’s about maintaining system integrity and predictable performance when standard materials would otherwise turn into brittle plastic or liquid goo.