Hydraulic applications are challenging to seal. Not only must the hydraulic seals prevent fluid leakage from the cylinder, but they also must withstand high pressures, extreme temperatures and transverse forces within the cylinder. Additionally, hydraulic systems require a complex combination of specialized seals, rather than a single seal. Hydraulic rod seals prevent fluid leakage from within the cylinder to the outside while hydraulic piston seals prevent fluid from flowing across the cylinder head. This allows pressure buildup on one side of the piston, making the cylinder extend or retract. Wear rings guide the piston and piston rod within the hydraulic cylinder, absorbing transverse forces and preventing metal-to-metal contact. Scrapers or wipers remove dirt, chips or moisture from the piston rods as they retract into the cylinder, preventing contamination.
These systems must stand up to extreme pressures, destructive process chemicals and marine environments.
Trelleborg Sealing Solutions
04/17/2017
Image 1. Oil and gas engineers must place close attention to the hydraulic pressure their systems are under due to the extreme conditions. (Images courtesy of Trelleborg Sealing Solutions)
Image 2. The V-stack seal assembly consists of a nest of chevron rings. This configuration provides an energizing axial force transferred from individual rings so that each ring has positive contact with the mating hardware surface.
The V-stack is a multi-component rod seal using multiple chevrons or “Vees” to produce a high-integrity seal with multiple redundancy points. These are typically used in rod or piston sealing on downhole tools, particularly on hydraulic setting tools for packers or plugs where conditions are challenging.
V-stacks can cope with high temperature and pressure, especially when combined with unknown hardware conditions or “blind stab” applications. The seal can have several Vees in differing materials, usually mated with PEEK anti-extrusion and adapter rings.
Metallic springs are the alternative to an elastomer to provide elasticity. Spring-energized seals are one of the most proven sealing solutions in oil and gas applications. They can be used in many regions, in a range of operating conditions and with a variety of media. The seal provides good low-friction properties and can be used on its own or paired with a PEEK anti-extrusion ring and support ring, or even Vee rings for high pressures.
The spring of the spring-energized seal is housed in a PTFE-based jacket, and being a completely non-elastomeric sealing solution, it withstands oil- and gas-related media while operating from -200 to 230 C. Special designs can function as a scraper in subsea hydraulic cylinders, such as valve actuators on subsea trees.
To specify the optimum seals for a hydraulic application, operators should talk to a seal specialist. Tools to assist in initial selection include an online compatibility check; engineers can input the media that sealing systems will be exposed to and it provides the best recommendations of compound types to use.