Development and Application of Bonnetless Gate Valves

Abstract: Traditional bolted-bonnet gate valves suffer from structural complexity, heavy weight, high production costs, and flange leakage risks. To overcome these shortcomings, a new bonnetless gate valve was developed using patented integrated-body technology. This paper details the one-piece body design, the internal assembly configuration, and the key fabrication procedures. Prototype type testing confirms that the valve meets the requirements of API 6D and GB/T 12224 for shell strength, high- and low-pressure sealing, pressure-assisted cycling, and critical-component mechanical properties. This design entirely eliminates the potential leakage path at the body-bonnet flange, while also substantially reducing valve weight, streamlining assembly and machining workflows, and improving overall production efficiency. This design offers a new approach to gate valve development, with the potential to enhance performance, reduce weight, and improve reliability.

As one of the most common isolation valves in pipeline applications, the gate valve's reliability directly affects the safety and stability of the overall system. Traditional gate valves generally consist of a body, bonnet, gate, stem, packing box, and actuator, with the body-bonnet connection employing a bolted flange design, as shown in Figure 1. While this design is technologically well-established, it suffers from several intrinsic disadvantages. Foremost among these is the proliferation of bolted connections, which increase structural complexity and parts count, thereby adding considerable weight and material expense. Second, the body-bonnet flange joint is inherently susceptible to leakage, since its seal relies on precise flange surfaces, adequate bolt preload, and reliable gasket behavior. These factors render the seal particularly prone to failure under pressure fluctuations, temperature changes, or corrosive service environments. Third, the complex design necessitates multiple machining steps and results in poor assembly efficiency.

1. Valve body 2. Bonnet 3. Bonnet flange bolted connection assembly 4. Valve stem 5. Hand wheel 6. Stem nut 7. Gland 8. Stuffing box 9. Bonnet flange gasket (potential leakage point) 10. Gate

Figure 1 Schematic of a traditional gate valve with bolted bonnet

The progressive implementation of national "carbon peaking" and "carbon neutrality" strategies has placed elevated demands on industrial equipment, particularly regarding energy efficiency, material conservation, and service reliability. At the same time, stringent zero-leakage requirements are being imposed on valves used in key industries such as petrochemicals and power generation. Therefore, developing a new type of gate valve that offers a simpler design, lighter weight, zero external leakage, and improved production and assembly efficiency is of great engineering value and market potential.

The bonnetless design provides a fundamental remedy for these problems. By integrating the body and bonnet into one monolithic unit, this approach entirely removes the conventional bolted flange joint. A company has conducted extensive R&D in this area and has been granted an invention patent for "bonnetless Gate Valves and Globe Valves" (ZL 2021 1 0509635.4), as well as several design patents (Figure 2) and utility model patents for bolt gate valves. Based on this patented technology, this paper presents a detailed account of the structural design and critical manufacturing processes for bonnetless gate valves, and verifies their overall performance through type-test reports from authoritative national testing institutions.

Figure 2: Design patent drawing of the bonnetless gate valve

The key innovation of the bonnetless gate valve resides in its one-piece body design and distinctive internal assembly arrangement, as shown schematically in Figure 3.

1. Integrated valve body 2. Gate 3. Valve stem 4. Upper sealing seat 5. Stuffing box assembly 6. Yoke 7. Packing locking nut 8. Thrust bearing 9. Stem nut 10. Round nut 11. Hand wheel 12. Stem nut locking nut 13. Stud bolt 14. Hex nut

Figure 3: Schematic of the bonnetless gate valve configuration

The valve body serves as the pressure-retaining main body and structural framework of the valve, making its design the most crucial element of bonnetless technology. Rather than a split-body configuration, this design employs an integral casting or forging process.

(1) To guarantee structural pressure-bearing capacity, the valve body's length, connecting flange dimensions, flow passage diameter, and minimum wall thickness are all designed and calculated per relevant standards, including GB/T 12224-2015 and ASMEB16.34. This ensures sufficient strength and stiffness to resist internal pressure and external loads.

(2) The valve body encloses a fully sealed cavity to house the gate. To allow insertion of the gate assembly, an enlarged assembly opening is usually incorporated on one side of the body. The passage diameter must be larger than the outer diameter of the gate, allowing the gate to be tilted and inserted into the internal cavity.

(3) Upper structure: The packing cavity is machined directly into the upper part of the body, housing the packing and gland to provide a dynamic seal for the stem. This configuration is integrated directly into the valve body, effectively removing the static seal leakage path that would be present between a separate bonnet and the body.

A T-slot connection couples the gate to the stem (Figure 4). This design absorbs minor dimensional and assembly deviations, promoting proper gate-to-seat sealing surface alignment during the closing stroke.

1. T-head 2. Gate 3. T-slot 4. Stem

Figure 4: Schematic of the gate-to-stem T-slot coupling

Owing to the integral (single-piece) construction of the valve body, the gate must be introduced through the flow passage.The assembly is carried out in the following sequence. First, the gate is inserted through the assembly passage into the body cavity and positioned. Next, the stem is introduced through the stuffing box opening at the top and mated with the T-slot in the gate. Finally, the packing and gland are installed. This assembly method necessitates a composite gate construction and imposes stringent requirements on internal spatial compactness. The assembled valve is shown in Figure 5.

Figure 5: The assembled bonnetless gate valve

The sealing system for the bonnetless gate valve comprises two primary elements, as illustrated in the comparison provided in Figure 6.

1. Intermediate flange 2. Back seat (upper seal) 3. Stem dynamic seal

(a) Leakage points in a conventional gate valve (b) Leakage points in a bonnetless gate valve

Figure 6: Comparison of leakage points between a conventional gate valve and a bonnetless gate valve

(1) Main seal (seat seal): The seal between the gate and the valve body seat. The seat can be formed either by hard-facing the valve body directly with a hard alloy (e.g D507Mo) followed by machining and lapping, or by embedding a prefabricated hard-faced seat into the body using an interference fit or welding. The sealing surface hardness must exceed 40 HRC, and the surface roughness must be better than Ra1. 6 μｍ to ensure excellent sealing performance and wear resistance.

(2) Stem seal (packing seal): This is the valve's only external dynamic sealing point. High-performance flexible graphite, PTFE, or composite packing is used, and sufficient preload is applied via the packing gland to achieve zero leakage at the stem. While conventional gate valves are susceptible to leakage at three locations—the bonnet-to-body static seal, the stem dynamic seal, and the backseat seal—the bonnetless configuration inherently eliminates the bonnet-to-body static seal as a potential leak point.This leaves the stem dynamic seal and back-seat seal as the only remaining leak paths, thereby reducing the total number of potential leakage points by one-third and delivering a substantial gain in overall safety.

Despite its many advantages, the integrated bonnetless configuration presents notable manufacturing challenges, particularly with regard to valve body forming.

Traditional split-body valves are comparatively easy to cast, whereas integrated bonnetless valve bodies contain complex internal geometries, including blind cavities that accommodate the gate.Conventional sand casting is prone to defects such as shrinkage cavities, porosity, and sand inclusions, and presents significant difficulties in sand removal. While forgings provide a dense micro-structure, they are ill-suited for directly forming complex internal geometries, and the required subsequent machining is both extensive and expensive. Both research and field applications suggest that Lost Foam Casting (LFC) is well-suited for producing rough castings of complex, integrated valve bodies.

The process sequence is as follows:

Pattern Production (fabrication of the foam plastic pattern)

Coating Preparation (application of a refractory coating)

Molding (compaction of dry sand by vibration)

Pouring (replacement of the foam pattern by molten metal)

Shakeout and Cleaning (removal and cleaning of the casting)

(1) A foam plastic pattern (white pattern) is produced from EPS or STMMA, precisely matching the valve body geometry.

(2) The individual white patterns are grouped into clusters, coated with a refractory slurry, and subsequently dried to prepare them for molding.

(3) The dried pattern clusters are placed into a flask, surrounded by dry sand, and the sand is compacted through application of mild vibration.

(4) Upon pouring, the molten metal's high temperature causes the foam pattern to vaporize completely. The metal subsequently fills the void and solidifies, yielding a dimensional precise valve body casting.

This process does away with traditional casting steps such as parting, pattern removal, and core making. Particularly well-suited for components featuring complex geometries and irregular internal cavities, this process delivers high dimensional accuracy with minimal machining allowance, while reliably ensuring the integrity and quality of internal flow passages and cavity surfaces.

(1) Gate: In contrast to traditional casting, a sheet metal forming process is adopted. This process orients the grain flow along the principal stress direction, yielding a denser micro-structure. Consequently, thickness—and thus weight—can be reduced while maintaining mechanical strength. The sealing surfaces are overlaid with a hard alloy via hard-facing, after which they are precision-turned and ground to achieve the required design specifications.

(2) Valve Stem: The manufacturing sequence begins with forging of highquality stainless steel (20Cr13), followed by rough machining, quenching and tempering,and precision grinding—ensuring adequate strength, hardness (HRC 30–40), and wear resistance.

Comprehensive type testing on the prototype WZ41H25 bonnetless gate valves was carried out by the Fujian Special Equipment Inspection and Research Institute for this study. The test samples comprised the WZ41H-25 DN80 (Product No.: LM/Z25070013) and WZ41H-25 DN150 (Product No.: LM/Z2507019), as depicted in Figure 8. Testing was carried out in strict compliance with standards TSG D7002-2023 (Rules for Type Testing of Pressure Piping Components) and GB/T 12224-2015.The main specifications were as follows: nominal pressure PN25, WCB body material, service media including water, steam, and oil, and a temperature range of –29 °C to 425 °C. The test outcomes confirmed the design’s reliability and performance advantages.

(a) WZ4lH - 25 DN80 (b) WZ41H -25 DN150

Figure 7 Bonnetless gate valves

Type testing encompassed comprehensive inspections—including appearance, marking, materials, strength, sealing, and operational performance. Key data are presented in Table 1, and the shell pressure test setup is shown in Figure 9.

Figure 8 Schematic Diagram of Valve Shell Pressure Test

(1) Structural Integrity and Pressure-Bearing Capacity: The shell test passed on the first attempt, and wall thickness measurements consistently exceeded the minimum values required by the standard. This confirms the soundness of the integrated valve body design—delivering excellent pressure capacity and structural integrity, and fully meeting the PN25 rating.

(2) Superior Sealing Performance: The valve passed both high-pressure water and low-pressure air seal tests with zero visible leakage—far exceeding the trace leakage limits allowed by the standard. This confirms the precision of the gate-and-seat sealing interface and the robustness of the stem packing seal—both of which contribute to achieving zero leakage as designed.

(3) High reliability and durability: The valve completed 20 pressure cycles smoothly, showing no binding or excessive wear, and sealing performance held up without any decline. This confirms that the stem-packing and gate-guide-rail interfaces are properly fitted, and that the components are designed to resist wear—ensuring long-term reliability in service.

(4) All key components meet the required mechanical property specifications: When subjected to tensile testing, the valve stems fractured in the threaded area outside the pressure boundary—at loads well above the design requirements. This validates the weak-link design philosophy: under overload, failure is confined to a non-critical zone. Meanwhile, sealing surface hardness exceeding 40 HRC ensures robust galling and wear resistance.

The design and test results presented above confirm that the bonnetless gate valve offers several distinct advantages over traditional gate valves, namely:

(1) Reduced external leakage risk: Elimination of the intermediate flange connection removes this static seal point entirely, cutting the number of potential external leakage sites from three to two (with only the stem packing remaining). This represents a qualitative leap in safety, making the valve particularly suitable for toxic, hazardous, flammable, explosive,and other severe service conditions. 

(2) Lightweight design and material savings: By eliminating dozens of components—including the bonnet, bolts, nuts, and gaskets—the valve achieves a more compact and lightweight design. Real-world measurements confirm a 33% weight drop across the same specifications, right in step with national energy efficiency and emission reduction goals.

(3) Enhanced production efficiency: In machining terms, the elimination of all bonnet and flange processing steps—including flange-face milling, bolt-hole drilling, and tapping—results in a roughly 30% reduction in machining duration. Assembly operations are considerably simplified through the elimination of gasket and bonnet installation, bolt tightening, and other related steps, yielding an increase in assembly efficiency exceeding 40%. Life-cycle cost analysis reveals substantial savings across multiple dimensions: component reduction lowers procurement, warehousing, and administration costs; decreased weight reduces logistics and installation expenses; and heightened reliability diminishes maintenance frequency and production losses, yielding significant cumulative economic benefits over the product's service life.

Following its initial deployment in early 2024, the bonnetless valve has been put into operation across numerous mission-critical environments, including petrochemical facilities, thermal power plants, and municipal pipeline networks. The unit with the longest service history has been running for over a year now, and field feedback has been consistently positive—performance is stable and reliable, with zero failures or abnormalities on record. Figure 10 provides a real-world view of the valve in operation.

Figure 9 Typical Field Installation of a Bonnetless Gate Valve

This paper describes a bonnetless gate valve that incorporates an integrated structural design. To overcome the manufacturing challenges posed by the one-piece valve body, we turned to advanced techniques like lost-foam casting, while concurrent optimization efforts ensured that structural strength and functional integrity were fully preserved. The valve has passed type tests at nationally accredited laboratories, with all performance indicators meeting or exceeding the required standards. Most notably, it has set a new standard for sealing reliability—achieving zero external leakage.

The bonnetless gate valve is a major breakthrough in gate valve design, delivering reliability, light weight, and efficiency in a single package. This development gives users a safer, more economical option while also advancing the state of the art and driving industrial upgrading across the valve sector. Future research directions may include:

(1) Material expansion: Extending the bonnetless design to additional materials—including austenitic stainless steel, duplex stainless steel, and high-temperature alloys—would enable the valve to withstand severe conditions involving corrosive media and high thermal loads.

(2) Higher Pressure Ratings and Larger Sizes: Future work will involve the design and validation of bonnetless gate valves for elevated pressure ratings (e.g. Class 600 and Class 900) and increased nominal sizes (e.g. DN500 and larger).

(3) Intelligent integration: Additional efforts will focus on developing compatible electric and pneumatic actuators and smart positioners, alongside integrating pressure and temperature sensors, thereby facilitating online condition monitoring and predictive maintenance.

(4) Standard establishment: promoting the development and refinement of design, manufacturing, and inspection standards for bonnetless valves to support and accelerate their broader adoption in the industry.