Control valve seals should not be replaced with pressure seal bonnets due to compatibility issues and the need for specific sealing materials for optimal performance.
In a Nutshell:
Whether it's control valves for high-pressure conditions or not, the question always arises: can Pressure Seal Bonnet technology be employed? Indeed, it's a valid query, especially in industries dealing with high-temperature steam or critical hydrocarbon services. Over the years, here's what we've learned.
High-Pressure Control Valves and Bonnet Technology
At the heart of the conundrum lies the Pressure Seal Bonnet and the traditional Bolted Bonnet. Let's explore both and debunk the myths surrounding their application.
Pressure Seal Bonnet - The Underdog
Pressure seal valves leverage internal pressure to seal more effectively. The bonnet is inserted into the valve body and held by a segmented thrust ring. As pressure increases, it pushes the bonnet upward, compressing the gasket tighter, making the structure compact and light for high-pressure situations (ANSI Class 900 and above).
Unique compared to traditional designs, the pressure seal bonnet's body-bonnet joint seal improves as internal pressure increases. In other words, the higher the internal pressure, the greater the sealing force. Easy dismantling makes these valves a reliable choice for challenging isolation application conditions in power plants and combined-cycle steam systems.
Manufacturers offer diverse materials like A105, WCB cast steel, and stainless F316/F316H, designed to withstand temperatures above 500°C.
Bolted Bonnet - The Veteran
Simple and robust, this design boasts a flange-to-flange structure held together by bolts and gaskets. It's easy to maintain and works well in low to medium pressure scenarios (most common in ANSI Class 150 to 600 systems).
Pressure Seal Bonnet or Bolted Bonnet? Why Not Both?
The question of which is better boils down to the specific demands of the application. While pressure seal bonnets offer excellent performance in many high-pressure isolation valve applications, they face technical challenges when it comes to control valves. To validate this, we even performed finite element analysis, but the challenges made the design impractical.
Fisher, Masoneilan, and other top brands haven't adopted pressure seal bonnets for their control valves for this reason. Cost, increased manufacturing complexity, and the infrequent need for high-pressure control valve applications contribute to this decision.
On the other hand, bolted bonnets remain the go-to choice for control valve designers due to their compatibility with the pressure range, stability during variable operation, structural alignment, and better handling of frequent actuation.
Multi-Packing Group Sealing - The Hybrid Solution
For high-pressure application needs, we rely on multi-layer packing structures, ensuring tight stem sealing, excellent chemical resistance, ease of maintenance, and more without the structural complexity of a pressure seal bonnet.
Wrapping It Up
Though Pressure Seal Bonnet technology shines in high-pressure isolation valve applications, its challenges in control valves make bolted bonnets a more practical and reliable choice. If you're evaluating valve options for a high-pressure system, our team is here to guide you with real-world engineering experience, helping you make the best selection for your needs.
- In the realm of technology, especially in the manufacturing industry, the debate between Pressure Seal Bonnet and Bolted Bonnet design for high-pressure control valves arises frequently, considering their impact on finance due to cost and manufacturing complexity.
- While Pressure Seal Bonnet technology stands out in high-pressure isolation valve applications, bolted bonnets, known for their compatibility with the pressure range and stability during variable operation, remain a preferred choice for control valve designers, often making them more practical and reliable.
