Basic Components of Hydraulic Cylinder Seals
Piston Seals
Piston seals provide the power for your hydraulic cylinder by preventing hydraulic fluid from flowing past your piston. This makes piston seals one of the most important hydraulic cylinder seals in your system.
The seal formed by a piston seal keeps contact between the piston and the cylinder bore, helping to control the motion of your cylinder and keeping your cylinder at the same position when at rest — even when it’s under a load.
Piston seals can be either single- or double-action. As mentioned earlier, a single-action piston has hydraulic fluid on only one side of the piston, which means that the piston seal must remain extremely close to the bore, otherwise fluid can seep through and lessen the effectiveness of your cylinder.
Double-acting cylinders, as the name implies, have hydraulic fluid on both sides of the piston. Because of this, the shape of a double-acting piston seal is symmetrical, possessing the same sealing properties in both directions.
These seals can also allow for more clearance between the piston and the cylinder bore, as they are not designed to prevent fluid leakage.
Rod Seals and Buffer Seals
Rod seals perform two seemingly contradictory functions. First, they keep hydraulic fluid from leaking outside of the cylinder during operation. However, these seals are also responsible for ensuring that there is a thin layer of lubrication on the piston rod. This not only prevents corrosion but also lubricates other important parts of your cylinder.
Depending on the duty level of your cylinder, you may or may not also have a buffer seal, which is set further within the cylinder, past the rod seal. These hydraulic cylinder seals are intended to smooth out the pressure within your cylinder, preventing pressure peaks resulting from external factors. They also prevent any contaminants within the cylinder, such as metal flakes, from causing damage to your rod seals.
Wiper Seals
Sometimes referred to as dust seals, excluders, or scrapers, wiper seals protect your equipment by preventing contaminants from entering your cylinder as the piston rod retracts.
Since the piston rod is coated with a thin layer of fluid to prevent corrosion, it can also pick up dirt and other contaminants, which could quickly damage the interior components of your cylinder. Wiper seals keep these contaminants outside of your system.
Guide Rings
These seals are intended to maintain moving parts in the proper position throughout the process of relative motion. In addition to keeping the important components properly aligned, guide rings prevent any metal-on-metal abrasion that might occur during operation, preserving the life of your equipment.
These seals also add another level of protection against contaminants by keeping your more sensitive seals safe from added wear.
Materials of common Hydraulic Cylinder Seals
Rubber
Rubber seals are used in situations that require a high degree of flexibility and compressibility. Nitrile butadiene rubber (NBR), fluoroelastomer (FKM), and hydrogenated nitrile butadiene rubber (HNBR) are all commonly used to fabricate dynamic cylinder seals. They possess good resistance to grease, mineral oils, and other hydraulic fluids.
PTFE
Polytetrafluoroethylene (PTFE) offers superior durability under extreme conditions, including temperature, pressure, and caustic chemicals. PTFE also has a very low coefficient of friction, which means that it requires less lubrication than other seals and can actually function quite well in dry operation.
Rigid Plastics
Encompassing a wide range of materials, plastic hydraulic cylinder seals offer moderate resistance to temperature and pressure, as well as chemical reactivity.
The durability of a plastic seal is largely dependent on the quality of the material itself, which can range from engineered plastics, which are superior to commodity plastic, to high-performance plastics. Because they have less flexibility than rubber or PTFE, these seals focus more on adding strength to your cylinder.
Thermoplastic Elastomers
Thermoplastic elastomers, or TPEs, combine the strength of plastic with the flexibility of rubber, which means that they stand up to high use while also providing superior elasticity. These hydraulic cylinder seals are highly resistant to abrasion and tearing and will maintain a constant pressure for longer than other materials can.
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