New technology addresses control valve stem seal maintenance, regulatory issues
Packing serves as the primary valve stem sealing system in today’s control valves. This seal typically incorporates a mixture of packing rings that are compressed against the valve stem to eliminate or reduce process fluid leaks.
Patented seal technology from Woodward provides a solution to common stem seal problems by creating a pressurized, viscous barrier between a set of high-pressure seals to prevent process fluids from leaking to the atmosphere.
Packing serves as the primary valve stem sealing system in today’s control valves. This seal typically incorporates a mixture of packing rings that are compressed against the valve stem to eliminate or reduce process fluid leaks. Packing material is typically made of Teflon or graphite-based materials and is selected on the basis of application conditions. Rings are compressed with a packing follower that can be manually adjusted or "live-loaded" with springs that apply continuous sealing force. The packing seal system functions by creating a tight seal between the material and valve stem.
High friction loads lead to seal wear and contamination and make these types of packing seals subject to frequent maintenance. As the valve strokes during normal operation, the valve stem abrades the packing material. Over time, the seal wears, and the packing needs to be repaired or replaced.
Seal contamination is another significant source of packing system maintenance. In an open bonnet valve design, the valve stem area is exposed to the surrounding environment. Foreign material (dust, dirt, corrosives), common in a plant environment, clings to the valve stem and is pulled through the seal system, causing seal damage.
If the seals are not properly maintained, fluid can leak past the packing box into the atmosphere. Leakage can be an environmental or safety concern—or both—depending on fluid type. The Clean Air Act limits fugitive valve emissions (fluid leaks) for hydrocarbon-based fluids, measured at the point of origin. Plants that do not meet fugitive emissions standards may be subject to stiff penalties. Regulatory requirements, combined with poor sealing performance, can greatly increase the cost of valve monitoring and maintenance.
A patented E3 Seal technology recently introduced by Woodward provides one solution to common stem seal problems. This new design creates a pressurized, viscous barrier between a set of high-pressure seals, preventing process fluids from leaking to the atmosphere. This system also lubricates the valve stem and protects it from environmental debris and corrosion, significantly extending the required maintenance interval over that of traditional packing systems.
The advanced E3 Seal technology, part of the company’s new GVP-100 control valve system, eliminates fugitive emissions and helps users comply with Clean Air Act standards and state emissions mandates without need for frequent routine stem seal maintenance.
Click here to read more from Control Engineering on the GVP-100 control valve.
—Edited by Jeanine Katzel, senior editor, Control Engineering, email@example.com