I. Definition and Structure​

A cast iron gate valve is a type of valve primarily made of cast iron, with a gate plate as its core component. The gate plate moves vertically to fully open or close the pipeline. Based on the sealing surface design, it can be categorized into ​wedge-type gate valves​ (single gate, double gate, flexible gate) and ​parallel gate valves​ (single gate, double gate).

Key Components:

• Includes door frame, door body, sealing surface, guide rails, and actuating devices (e.g., screw rods, handwheels).
• The door frame and door body are connected via guide rails to ensure vertical movement of the gate plate.
• Sealing surfaces are typically made of rubber or metal materials, achieving tightness through compression.

Actuation Types:

• ​Rising stem: Exposed valve stem driven by threaded rotation.
• ​Non-rising stem: Valve stem enclosed within the body, rotated to drive the gate plate.

​II. Working Principle​

Sealing Mechanisms:

1. ​Self-sealing: Closure relies on medium pressure pressing the gate plate against the seat, suitable for high-pressure environments.
2. ​Forced sealing: External force (e.g., handwheel or actuator) compresses the gate plate and seat, common in medium-low pressure scenarios.

Operation Process:

• Rotate the handwheel or electric actuator to drive the screw rod, lifting or lowering the gate plate.
• Fully open position minimizes fluid resistance; fully closed position ensures a perfect seal.

​III. Materials and Types​

Material Classifications:

1. ​Gray Cast Iron Gate Valves:
   • Low cost, moderate corrosion resistance.
   • Ideal for ambient temperature and low-pressure applications (e.g., municipal water supply).
2. ​Ductile Iron Gate Valves:
   • High strength and toughness, with rubber-coated sealing surfaces.
   • Suitable for chemical and water treatment in medium-pressure environments.

Derived Types:

• ​Flexible Seated Gate Valves: Compensate for sealing surface misalignment, enhancing leak resistance.
• ​Non-rising Stem Gate Valves: Integrated valve stem and gate plate design, ideal for space-constrained installations.

​IV. Applications​

1. ​Hydraulic Engineering:
   • Used in sluice gates, pump stations, and large-diameter pipelines to control water flow.
2. ​Petrochemical Industry:
   • Transports corrosive media (e.g., acids, alkalis) with ductile iron’s chemical resistance.
3. ​Water Treatment Systems:
   • Cuts off or regulates water levels in sewage plants, with flat designs to prevent sediment buildup.
4. ​Energy Sector:
   • Controls steam flow in thermal and nuclear power plants under high-temperature and pressure conditions.

​V. Advantages and Limitations​

Advantages:

• Cost-effective and low maintenance, ideal for budget-limited projects.
• Strong corrosion resistance (especially ductile iron in humid environments).
• Stable sealing performance with flexible seats to minimize leakage.

Limitations:

• Less suitable for extreme high-temperature or high-pressure environments compared to carbon steel valves.
• Higher flow resistance and slower opening/closing speeds.

​VI. Maintenance and Precautions​

Installation Requirements:

• Install vertically to ensure gate plate alignment with the seat, avoiding jamming.
• Open bypass valves before operation to balance pressure differences.

Routine Maintenance:

• Lubricate valve stem threads monthly to prevent rust.
• Inspect sealing surfaces regularly and replace worn rubber components.

Troubleshooting:

• Address leaks by checking wedge tightness or sealing surface deformation.
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