What is the working principle of high pressure sealing gate valve?

High-pressure sealing gate valves are critical fluid control devices designed for demanding conditions (e.g., high pressure, high temperature, or corrosive media). Their core function relies on specialized designs to achieve reliable sealing. Below is a detailed breakdown of their working principle.

1. Basic Structure

1. Valve Body

   • The pressure-bearing component, typically made of forged steel (e.g., A105) or alloy steel (WC6), featuring a full-bore design to minimize pressure drop.

2. Gate (Disc)

   • Solid Wedge: Cast as a single piece for stable performance in high-pressure applications (e.g., Class 600 and above).

   • Flexible Wedge: Incorporates springs or hinges to adapt to minor seat deformation, improving sealing.

3. Valve Seat

   • Hard-sealed (e.g., Stellite overlay) or soft-sealed (PTFE), forming a sealing pair with the gate.

4. Stem

   • A rising-stem design connected to the gate via threads or a T-slot, requiring high-pressure and corrosion-resistant materials (e.g., 17-4PH stainless steel).

5. Stem Packing System

   • Multi-layer graphite or PTFE packing, combined with a gland to prevent leakage around the stem.

2. Sealing Mechanism

(1) Bidirectional Sealing

• Metal Hard Sealing (common in high-pressure applications):

  • When closed, the gate is pressed axially against the seat, creating line contact or surface contact sealing.

  • Relies on high-precision machining (Ra ≤ 0.8μm) and material hardness (e.g., seat HRC 50+) to prevent media penetration.

• Soft Sealing (auxiliary for low pressure):

  • Uses PTFE or rubber embedded in the seat for zero leakage at low pressure, often serving as a backup in fire-safe designs.

(2) Pressure-Enhanced Sealing

• Under high pressure, media forces the gate tighter against the seat (e.g., wedge gate valves), creating a pressure-assisted seal where sealing force increases with system pressure.

(3) Critical Sealing Points

• Gate-to-Seat Interface: The primary sealing surface, resistant to erosion and particle wear.

• Stem Packing Seal: Pre-compressed packing prevents leakage along the stem.

• Body-to-Bonnet Seal: Uses spiral-wound gaskets or ring-joint gaskets.

3. High-Pressure Adaptations

1. Reinforced Structure

   • Valve body thickness calculated per ASME B16.34 to prevent deformation.

   • Gate reinforcement ribs prevent bending under high pressure.

2. Fire-Safe Design (API 607/6FA)

   • If soft seals burn away, metal seats maintain sealing (e.g., dual-seal systems).

3. Blowout-Proof Stem

   • Stem features a shoulder at the base to prevent ejection under high pressure.

4. Typical Operation Sequence

1. Opening Process

   • Rotating the handwheel or actuator raises the gate vertically, fully opening the flow path (full-bore design ensures <5% pressure loss).

2. Closing Process

   • The gate descends, initially disengaging from the seat to reduce friction before final sealing. High-pressure valves often require additional torque for tight closure.

3. Sealing Tests

   • Factory high-pressure gas tests (per API 598, test pressure ≥1.1x rated pressure).

5. Key Selection Considerations

• Extreme Conditions: For ultra-high pressure (≥Class 2500), choose parallel slide or double-disc gate valves.

• Corrosive Media: Apply WC or CrC coatings on seats for extended service life.

• Actuation Method: High-pressure valves should use electric/hydraulic actuators (e.g., thrust ≥10kN).

Conclusion

High-pressure sealing gate valves achieve reliable shutoff via precision metal sealing, pressure-assisted enhancement, and reinforced construction. Selection must account for pressure class, media properties, and safety standards (e.g., API 6D), with regular maintenance of sealing systems ensuring long-term performance.