In-Depth Analysis of SD61H-P38.5 Self-Sealing Mechanism

 In-Depth Analysis of SD61H-P38.5 Self-Sealing Mechanism

In the maintenance of power plant boilers, the sealing performance of block valves (plugs) in the reheater and superheater is directly related to the safety of the hydraulic test and the efficiency of unit start-up. As a critical core component, the self-sealing ring, such as the SD61H-P38.5 used in block valves, is widely adopted in 300MW–600MW subcritical and supercritical units due to its unique characteristic: "The higher the pressure, the better the seal."

What is the sealing mechanism behind this characteristic?

The SD61H-P38.5 is not an ordinary rubber O-ring. It is a wedge-shaped, self-enhancing sealing structure specially developed for high-pressure, high-temperature conditions, composed of a high-purity flexible graphite composite with a stainless steel skeleton.

The Principle of Self-Sealing

The cross-section of the sealing ring features a trapezoidal design and is installed in the annular groove between the block valve cap and the valve body.

When the system pressure rises, the medium pressure (water or steam) acts on the bottom of the valve cap. This force is transmitted through the inclined surface of the valve cap onto the wedge-shaped face of the sealing ring, generating a radial outward component force. This force compels the sealing ring to press more tightly against the sealing surface of the valve body. The higher the system pressure, the greater the compressive force, and consequently, the stronger the sealing effect. This is the core advantage of the "self-sealing" technology.

 Technical Advantages Compared to Traditional Gaskets

The SD61H-P38.5 self-sealing ring offers significant technical advantages over traditional gaskets or elastic rings:

• High Temperature Resistance: Withstands temperatures up to 550C, making it suitable for the harsh environments of the reheater cold/hot sections.

• High Resilience: Resilience rate  25\%, effectively compensating for thermal expansion and assembly tolerances.

• Creep and Oxidation Resistance: Ensures long-term operation without relaxation.

• Compliance: Meets power industry standards such as TSG 11-2020 and DL/T 438.

 Critical Installation Notes

It must be emphasized that optimal performance depends on standardized installation. If the valve cap is skewed, the liner ring height exceeds specifications (it should be 2mm lower than the six-segment split ring groove), or the six-segment split rings are not installed correctly according to their numbering, the sealing ring will be subjected to uneven forces. This will prevent effective sealing even under system pressurization, potentially leading to leakage.

We recommend strictly following these key installation points:

• Ensure the sealing groove is clean, burr-free, and free of scale.

• Install the valve cap horizontally and slowly, using a copper bar for gentle vibration to prevent jamming.

• Precisely align the six-segment split rings according to their numbering to ensure the valve cap remains freely floating.

• Tighten the bolts evenly in stages (cold state rightarrow 0.5MPa rightarrow full load) to eliminate eccentric loading.

HKZX-2025-12-10