Gate valves typically have designs such as single-wedge, double-wedge, wedge-type, parallel-type, etc. Among them, wedge-type double-wedge and wedge-type resilient gate valves are the most widely used, both achieving excellent sealing effects.

There may be an abnormal increase in central cavity pressure in certain situations due to its excellent double-sided sealing. The consequences of overpressure of gate valves can be extremely severe. When there is an abnormal pressure increase in the central cavity of the valve, the operational stress on the pressure-bearing components and the operating components (such as the stem and gate frame) will sharply escalate. The driving force of the actuator may become unbearable, leading to difficulties. In severe cases, the stem may fracture; the gate frame may break, and the motor may burn out. These phenomena are not uncommon in many high-pressure and large-diameter gate valves.

Hazards of Abnormal Pressure Increase
1. Damage to the valve
The strength of the valve casing, valve bonnet, and valve stem components is generally designed based on the nominal pressure of the valve. When abnormal pressure rise occurs, the opening pressure will increase exponentially, resulting in a doubling of the service stress of the relevant parts. When the actual stress of the material exceeds the allowable stress, high stress areas will experience fracture and damage, resulting in the valve being unable to open and the entire valve being damaged or scrapped.

2. Disruption to system security
Obviously, it is very dangerous when the pressure bearing parts such as the shell and valve bonnet are overpressure. Once overpressure occurs, the weak part may first undergo perforation, causing leakage. The packing and self-sealing ring parts are often scoured by high-pressure fluid, causing a large amount of leakage. When the media are high-temperature gas, toxic gas, or harmful gas, it can become even more serious, and even cause damage to equipment and personnel.

3. Causing significant losses to production control processes
The normal opening and closing of valves is the key to various industrial process control. Once this control cannot be achieved, the system will need to be shut down for maintenance, which will cause great losses.

Protection
1. Opening pressure relief holes inside the valve
The fundamental solution to abnormal pressure increase in the middle chamber is to balance the pressure in the middle chamber, and opening a pressure relief hole is the most economical and effective solution. Pressure relief holes are set up on the outer circle of the upstream gate and inlet valve seat. When the pressure in the middle chamber increases, the pressure in the middle chamber will automatically release towards the upstream side, always keeping the pressure in the middle chamber equal to the pressure on the upstream side, thereby avoiding the occurrence of abnormal pressure rise.

2. Special pressure relief valve for external installation of the valve
Install a pressure relief valve outside the chamber of the gate valve to control the pressure range. Set the discharge pressure of the relief valve to the rated working pressure of the main valve. When the middle chamber is overpressure, it automatically discharges to the set pressure to maintain the safe operation of the main gate valve.

Abnormal overpressure is a hidden killer of double seat gate valves, seriously threatening the safe operation of equipment and systems, and must be taken seriously. The occurrence of abnormal overpressure must be considered especially for high-temperature, high-pressure, and large-diameter gate valves, and take necessary preventive measures.