Cylinders can fail for a number of reasons from wrong specifications to operator error. However, in this day and age with a number of engineering tools available to help reduce spec errors and strong expertise within the fluid power industry, one of the leading causes of cylinder failure is still seals. Whether, the seals are sized wrong, incorrect material is spec’d, or just installed wrong, error in sealing can have a major effect on the entire cylinder operation.
Cylinder operation is based on precise fluid pressure to both sides of the piston. If a seal breaks down and allows fluid to leak from one side of the piston to the other or out of the cylinder all together, the pressures change, and your cylinder will no longer operate as intended. With over 100 years in the fluid power industry, Parker engineers have seen countless examples of how seal issues can escalate into much larger problems for a hydraulic system.
Seal issues tend to fall into three main categories: hardening, bad installation and erosion.
Seal hardening is exactly what it sounds like. The seal can solidify and dry out making it hard and brittle. The most common reason for this is exposure to temperatures that are too high for the seal to handle. Be warned this is not just ambient temperature around the cylinder. The piston itself can generate substantial heat through motion and friction causing wear to the seal. This heat can be monitored by measuring the temperature of the hydraulic fluid entering and exiting the cylinder. There are several methods to combat hardening including insulation and cooling, but the best way is to use materials that are suited for the temperature requirements for your application. Parker offers a number of high-temperature class seals to ensure you meet the heat requirements of your job.
While cylinder operation may seem simple on its surface, it takes precise installation of several parts to ensure that the cylinder will operate correctly for its entire life cycle. The seals are an integral part of this and if they are misaligned it can allow for hydraulic fluid leak past the seals. This can cause problems in cylinder operation that can lead to major failures that will result in costly downtime for your operation. Not only can Parker provide cylinders with the proper seals properly installed, we also offer universal seal kits to help ensure ease of installation on replacements, and our applications engineers have years of expertise to help when these installations get tricky.
Erosion can occur from three main sources. One cause is the general wear from the normal back and forth motion of the cylinder. This source unfortunately is unavoidable but can be prolonged thanks to the developments of Parker's Engineered Materials Group. The Engineered Materials Group develops and manufactures innovative sealing solutions to meet the challenges of today's vastly changing industries. Parker provides a wide range of specialty elastomers to satisfy unique sealing requirements with a combination of experience, innovation, and support.
Another source of erosion is pressure build-up. If the seal used in a cylinder is not specified to the appropriate pressure, pressure can get trapped underneath the seal and push it against the cylinder body causing wear.
Recently, Parker cylinder engineers identified an issue of a piston seal getting blow-by and causing the cylinder to drift in a hydraulic press application. They were able to identify that the seal thickness was varied from about 1/32” under to almost 1/16” underprint dimensions and that there was a slight amount of extrusion on the side of the seal facing towards the cap end of the cylinder. These would indicate higher pressure on the rod end of the cylinder that was getting trapped underneath the seal and pushing it against the cylinder body causing wear. Parker recommended switching from the KP piston seal to the HP that is made of polyurethane, a tougher material, with reliefs molded into the sides of the seal to allow venting excess pressure underneath. This helped the customer identify an issue early that could have grown into a much bigger problem.
The Parker HP energized bi-directional piston seal improves upon the low friction and long wear of lip seals by including excellent low pressure sealing performance. Specially formulated polyurethane is long-wearing and abrasion-resistant with running friction comparable to lip seals. An o-ring energizer ensures virtually zero leakage in low-pressure applications. Also, pressure trapping that can result in energized lip seals is not possible with a single energized seal.
Parker’s HP piston seal is an excellent choice for most industrial applications operating with mineral-based hydraulic oil and is available in Seal Classes 1 and 4.
The Parker KP bronze filled PTFE seal ring material has low running friction for accurate positioning in closed loop servo applications. When combined with a fluorocarbon energizing ring the Parker KP seal is rated for 400° F and will increase service intervals in high temperature applications when compared to fluorocarbon lipseals.
By combining the Parker KP seal with other energizer O-ring compounds and wear ring materials, the KP seal offers excellent service in all Seal Class environments.
The final main source of erosion is used with an incompatible fluid. Hydraulic systems use a relatively incompressible fluid, and given the application environment, different types of hydraulic fluids may be required. For example, the use of synthetic hydraulic fluid may be used for highly flammable applications. That is why you must keep in mind that not every seal will work with every application. If your job calls for a particular type of hydraulic fluid, customers should evaluate the seal material and compatibility to the fluid to ensure they have a seal that will withstand the chemical properties of that fluid. Parker offers seven classes of seals that are designed to work with standard hydraulic fluids to some that are highly corrosive.
Check out the Parker Sealing Technology Bulletin for more information on the wide variety of actuation sealing options Parker can provide. This bulletin shows how Parker seals provide unmatched leak protection on all industrial hydraulic and pneumatic cylinders. It gives ample information to help choose the right seal for your application. Download it now for all your sealing needs.
This article was contributed by Ryan Roberts, market specialist, Parker Hannifin's Cylinder Division.
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