Comparison of Underwater Flat Gate Valve Sealing Structures

Underwater flat gate valves play a vital role in oil and gas extraction and deep-sea operations, especially in terms of sealing technology. With the advancement of technology, the sealing structures of underwater gate valves have become increasingly diversified. Depending on the number of valve seats and the principle of sealing, underwater flat gate valve sealing structures can be classified into single-seat sealing and split-seat sealing. This article will explore the characteristics, working principles, and applicable scenarios of these two sealing structures in detail.

Single-Seat Sealing Structure

The single-seat sealing structure is the earliest sealing form used in underwater flat gate valves, with a relatively simple and mature design. The key feature of this structure is that each side of the valve plate has one valve seat, which is combined with a sealing ring assembly and spring device. Typically, a wave spring or C-shaped spring is used to ensure tight contact between the valve seat and the valve plate under low pressure conditions. The working principle of the single-seat sealing structure is as follows.

Each side of the valve plate has a valve seat, which is connected to the valve body through a U-shaped sealing ring assembly. When the valve closes, the medium flows into the valve body upstream, passing through the gap between the upstream valve seat and the valve body end face. The U-shaped sealing ring opens due to the pressure difference between its ends, forming a sealing barrier to prevent fluid from flowing downstream. Meanwhile, the upstream pressure pushes the valve plate into contact with the downstream valve seat, achieving a metal self-seal and preventing leakage into the downstream flow path.

Advantages: Simple structure and lower manufacturing costs, suitable for shallow sea areas with low pressure. Excellent sealing performance under low-pressure conditions, such as in oil and gas wells with lower pressure.

Disadvantages: The elasticity of the wave spring is limited, and long-term use may lead to spring failure, resulting in decreased sealing performance.

Split-Seat Sealing Structure

The split-seat sealing structure is more complex and divides the single valve seat into a front and rear valve seat. Representative products of this sealing structure include the HPT™ sealing structure used by NOVT3 and the Sual-Seat™ sealing structure used by WOM's Magnum gate valve. Depending on the design, the split-seat sealing structure can achieve unidirectional or bidirectional sealing.

1. HPT™ Sealing Structure

The HPT™ sealing structure combines front and rear valve seats in its design. The key features of this structure include:

Split Valve Seats: The front and rear valve seats are symmetrically arranged on both sides of the valve plate.
PEEK Material U-Shaped Sealing Ring: Two PEEK material U-shaped sealing rings are placed between the rear valve seat and the valve body end face to prevent oil and gas from leaking through gaps.
Metal Self-Seal: The upstream oil and gas pressure pushes the valve plate into contact with the downstream valve seat, forming a metal self-seal and ensuring no leakage downstream.
Anti-Sand Design: A stepped structure on the contact surfaces of the front and rear valve seats prevents solid particles in the oil and gas medium from entering the valve chamber, extending the valve's service life.
This structure is ideal for deep-sea high-pressure oil and gas mediums, providing a longer service life.

2. Sual-Seat™ Sealing Structure

The Sual-Seat™ sealing structure used by WOM combines axial and radial sealing rings to achieve bidirectional sealing. Its key features include:

Bidirectional Sealing: The design between the front and rear valve seats enables the valve to seal both upstream and downstream simultaneously when opened, making it suitable for complex operating environments.
Combination of Metal and Soft Seals: In the normal closed state, the front and rear valve seats move relative to each other. The sealing ring between the upstream front and rear valve seats forms a soft seal, while the rest of the structure uses a metal seal.
This design is particularly suited for higher-pressure media, offering better corrosion resistance, especially in acidic media and high-temperature environments.

Comparison of Sealing Structures

The sealing structures of underwater flat gate valves exhibit different characteristics in terms of application, advantages, and disadvantages.

1. Single-Seat Sealing Structure

Suitable for shallow sea areas and low-pressure oil and gas wells, this design is simple and cost-effective. Its advantages include a straightforward structure, low cost, and effective sealing performance in low-pressure environments. However, its drawbacks include a short spring lifespan, leading to a decline in sealing performance over time, and its unsuitability for high-pressure conditions.

2. HPT™ Sealing Structure

This structure is especially suited for deep-sea high-pressure oil and gas wells. Its advantages include excellent anti-sand design, strong sealing performance, and compatibility with high-pressure oil and gas mediums. However, its complex design results in higher manufacturing and maintenance costs, making it unsuitable for low-pressure or simpler applications.

3. Sual-Seat™ Sealing Structure

This structure is suitable for high-pressure, acidic, and high-temperature environments. Its bidirectional sealing ability and combination of metal and soft seals make it especially effective under such conditions. Its main disadvantage is the complexity of its design, and sealing components may fail after long-term use, requiring careful maintenance and management.

Conclusion

The selection of a sealing structure for underwater flat gate valves should be based on the specific working environment and pressure conditions. The single-seat sealing structure is suitable for shallow seas with low pressure, offering a simple structure and low cost. On the other hand, the split-seat sealing structure is more suitable for deep-sea high-pressure environments, offering higher sealing performance and durability, especially in terms of anti-sand and high-pressure capabilities. The HPT™ sealing structure extends the valve's service life through its unique anti-sand design, while the Sual-Seat™ sealing structure excels in high-pressure and acidic media applications. Choosing the appropriate sealing structure based on specific requirements is key to ensuring the long-term stable operation of underwater flat gate valves.