1. Overview

Electro-hydraulic plug valves, also known as spectacle valves, are one of the main shutdown devices in the coking coal gas pipeline network of ironmaking blast furnaces. Widely used in the metallurgical industry, these valves are critical shutdown equipment for the blast furnace gas dedusting system and the blast furnace gas pressure recovery turbine (TRT) power generation system.

2. Working Principle

Electrical or hydraulic plug valves are commonly used in conjunction with metal-sealed butterfly valves. Taking the closed hydraulic plug valve as an example (Figure 1), the opening and closing of the valve is composed of two parts: the lifting mechanism of the valve seat (hydraulic cylinder) and the valve plate movement mechanism (hydraulic motor). The valve plate is equipped with both through-hole seats and blind-hole seats. The switching between the through-hole seat and the blind-hole seat is achieved through several actions: lifting (releasing the valve plate) → horizontal movement of the valve plate → clamping (the valve plate sealing pair achieves sealing), thereby realizing the opening and closing of the valve. The lifting mechanism and the valve plate movement mechanism of the electrical plug valve are both driven by electric devices.

1. Limiting Device 2. Valve Plate Indicator 3. Auxiliary Valve Body 4. Main Valve Body 5. Valve Seat Elevation Mechanism 6. Valve Plate 7. Transmission Pinion Shaft 8. Valve Plate Travel Mechanism 9. Coupling 10. Motor

3. Fault Analysis

The valve plate's lateral movement is achieved by the chain wheel of the valve plate walking mechanism driving the transmission shaft at the bottom of the valve plate. During the factory debugging of the electric plug valve, after the valve plate reaches its position, the travel limit switch of the electric unit is adjusted to ensure that the electric unit stops running while the limit device achieves the positioning of the valve plate. For the hydraulic plug valve, during factory debugging, after the valve plate reaches its position, the travel switch for the valve plate's positioning is adjusted to ensure that the hydraulic motor stops driving while the limit device achieves the positioning of the valve plate. However, during use, the valve occasionally experiences a lag or failure in the travel switch.

Upon on-site analysis and confirmation, the failure of the electric device counter due to incorrect adjustment and the inertia collision of moving parts resulted in delayed or failed signals transmitted by the travel switch. This led to the continued operation of the electric device or hydraulic motor under overload, ultimately damaging the transmission shaft or coupling of the valve plate walking mechanism, causing an operational accident involving the blast furnace gas and its system.

4. Measures for Improvement

The Ratchet Safety Device utilizes the engagement and disengagement of a dull gear with the drive shaft to ensure the gear operates correctly. Once the gear is in position, the drive shaft promptly releases, allowing the gear to rotate freely without moving the rack frame, thereby activating its safety function. This device does not hinder the gear's reverse rotation. The Ratchet Safety Device typically employs a groove-type structure (Figure 2) and an adjustable pin-type structure (Figure 3). It is set at the two extreme positions of the valve plate's horizontal movement, ensuring the safety of all drive components of the valve plate mechanism through the free rotation of the dull gear away from the rack. The groove-type safety device is structurally simple and commonly used in open-type gate valves. The adjustable pin-type safety device is suitable for closed-type gate valves. During design, the diameter of the adjustable pin hole is appropriately increased, and an adjustable pin auxiliary return spring is added to ensure the normal horizontal movement of the valve plate.

5. Conclusion

The application of the销齿条safety device resolves the damage to valve drive components caused by lagging or failure of the stroke switch, ensuring the normal operation of the blast furnace gas process system.