Hydraulic cylinder seals can be manufactured from a number of different materials. Each material has different properties that make them better suited to different conditions, including high pressures and temperatures, as well as caustic chemicals. Here are the different materials you’re likely to encounter:
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.
Choosing the Right Hydraulic Cylinder Seals
Choosing the right seal is about more than materials, however. There are a number of external factors that you need to consider when you’re designing your cylinders. Each of these factors can go a long way toward determining which hydraulic cylinder seals you’ll need to ensure that your system can work efficiently for the long haul.
Cylinder Application
One of the most important considerations to keep in mind as you’re designing your hydraulic cylinder is to know precisely what you will need your cylinder to do. In general, you can break your application down into three different categories:
- Light Duty: Pressures up to 2,300 psi, temperature up to 70˚ C
- Medium Duty: Pressure up to 3,625 psi, temperature up to 90˚ C
- Heavy Duty: Pressure up to 5,800 psi or more, temperature over 90˚ C
Having realistic expectations about the duty level that you’ll require from your cylinder will ensure that you won’t end up having to replace your equipment prematurely. If you’re unsure where your cylinder falls, or if you think you’re right on the dividing line between two service levels, it’s usually a good idea to choose a heavier-duty model — just in case.
Temperature
You’ll need to know your average operating temperature, but also the temperature of your equipment when it’s at rest.
Speed
This is the speed at which your piston operates within your cylinder. Typically, the faster the cylinder operates, the hotter the cylinder will become.
Fluid Pressure
It’s important to know what kinds of pressure your cylinder will encounter, which is usually expressed as a range. You’ll also want to identify any pressure peaks, noting both intensity and frequency.
Hydraulic Fluid
There is a wide range of different hydraulic fluids available, and each fluid possesses a different viscosity, which will affect the hydraulic cylinder seals you’ll require.
Dimensions
The shape of your cylinder will also have an impact on which seals you’ll want to use in your cylinder. You’ll need to know the exact measurements of these parts:
- Rod diameter
- Bore diameter
- Stroke length
- Overall cylinder length
Each of these factors will play a part in determining other considerations, including pressure, speed, and power. These can go a long way in helping you choose the right hydraulic cylinder seals to keep your equipment working properly.