Proper hydraulic cylinder operation depends on choosing the best seal. A good working knowledge of the sealing options available, and what ultimately causes their failure, helps to achieve that goal.
Seals play an important role in hydraulic cylinders: they contain fluid and prevent fluid leakage between components. They are classified into two main categories: dynamic and static. Dynamic seals are used between parts that are in relative motion. The seals for a rod sealing system protect dynamic reciprocating motion for the rod and piston head. The dynamic reciprocal movement between the piston and the cylinder bore is another area of a hydraulic cylinder that uses dynamic seals.
Common failures of hydraulic seals
This cross section of a hydraulic cylinder highlights the crucial seals necessary for its operation.
Static seals are used between fixed components. In a hydraulic cylinder, static seals are typically employed between the piston and the piston rod, and between the cylinder head and tube.
The following is a list of dynamic seals and the special function each has in relation to cylinder performance:
Piston seal:
● They function as a pressure barrier.
● They prevent fluid from passing through the piston and are essential for maintaining the idle position and controlling cylinder movement.
Stem seal:
● They are a pressure barrier and keep the fluid operating inside the cylinder.
● The rod seal regulates the film of fluid, which spreads with the surface of the piston rod. This is important to prevent rod corrosion, lubricate the wiper seal, and lubricate the rod seal.
● Rod seals also accept the lubrication film as it returns to the cylinder when the rod is retracted.
Damping seals:
● When pressure spikes occur due to excess system pressure, cushion seals protect the rod seal from pressure build-up.
● Improve rod seal performance by attenuating fluctuations in system pressure. They allow the rod seal to operate with more constant or gradual pressure changes.
● They act as a filter against contaminants that can damage the rod seal.
Wiper seals ：
● Windshield wiper seals are important because of their ability to block the entry of external contaminants into the hydraulic system and cylinder assembly.
● They accept the lubrication film on the cylinder when the rod retracts.
Guide rings:
● Guide rings prevent metal-to-metal contacts between cylinder components.
● They keep the piston and rod position precisely centered. This is crucial to the performance of the piston and rod sealing system.
● They react against the radial load caused by lateral loads acting on the cylinder assembly.
Due to time of use or exposure to abuse, hydraulic seals will eventually fail and need to be replaced. A design engineer may be able to reduce the damage inflicted on hydraulic seals by taking into account the typical causes of failures and trying to avoid their damaging impact.
1. Hardening ：
Hydraulic seals become tough when exposed to high temperatures. This is due to high fluid operating temperatures in the application or high speed heat generation from stroke operations. When seals harden, they crack and lose elasticity, leading to seal failure.
2. Use ：
Whether due to insufficient lubrication or excessive lateral load, wear on the dynamic face of a sealing edge can cause considerable damage.
3. Healing ：
Installation tools and processes are important to the life of the seals. Improper installation can cause cuts or dents on the dynamic edge of the seal, which affects the efficiency of the hydraulic seal and also introduces foreign elements into the hydraulic fluid.
4. Fracture ：
Fracture is the condition that results in burns, breaks, long cracks, and a complete rupture of the dynamic side of the seal. This is due to excessive back pressure, high pressure spikes / spikes, or the use of poor quality materials during the seal manufacturing process.
5. Improper installation:
As mentioned above, improper installation can create problems with hydraulic seals. It can lead to dirt, unsafe handling, contamination, and incorrect sizing of the chosen seal. Deciding on the seal before building is important to ensure that the design is done correctly to ensure a proper seal. 6. Pollution:
The introduction of external floating debris and jetsam into the hydraulic rod causes contamination. When particles such as dirt, mud, dust, or other tiny elements adhere to the piston, they dirty the seal. The dirtier the seal, the more it loses its ability to hermetically prevent contaminants from the piston area.
7. Chemical erosion:
The seal material will decompose when it encounters a corrosive fluid. This will occur when the wrong sealing material is chosen for an application. The use of non-compatible materials leads to chemical attack of the oil additives, hydrolysis and / or reduction of oxidation of the sealing elements. This will result in loss of the seal edge interface, softening of the seal durometer, swelling and / or shrinkage of the seal. Joint discoloration is an indicator of chemical erosion.
