1. Hazards

 (1) Damage to the valve itself

The strength of valve shell, bonnet and stem parts is generally designed according to the nominal pressure of the valve. In case of abnormal pressure rise, the opening pressure will be doubled, resulting in the service stress of relevant parts to be doubled. When the actual stress of the material exceeds the allowable stress, the high stress part will break, causing the valve to fail to open, the whole valve will be damaged or scrapped.

 (2) Damage to safety system

Obviously, overpressure of pressure bearing parts such as shell and bonnet is very dangerous. Once overpressure occurs, the packing and self-sealing ring will be impacted by high-pressure fluid, causing medium leakage. When the medium is high temperature, toxic and harmful gas, it will even cause damage to equipment and personnel.

 (3) Cause huge losses to the production control process

The normal opening and closing of valves is the key of industrial process control. Once this control cannot be achieved, the system will be paralyzed, which will cause huge losses.

2. Protective Measures

 (1) Pressure relief holes can be set inside the valve

The fundamental solution to the abnormal pressure rise in the middle chamber is to balance the pressure in the middle chamber. Opening a pressure relief hole is an economical and effective solution. A pressure relief hole can be opened in the outer circle of the upstream side wedge and the inlet side valve seat. When the pressure in the middle chamber rises, the pressure in the middle chamber will automatically discharge to the upstream side, the pressure in the middle chamber will always be kept equal to the pressure in the upstream side, so as to avoid abnormal pressure rise.

 (2) Valve installs external bypass pressure relief

For valves that have been delivered, external bypass and external pressure relief valves can be installed to reduce the pressure in the middle chamber. The bypass with a globe valve is used to connect the middle chamber and the upstream side. When the main wedge is closed, the globe valve can be closed (Depending on the temperature change of the middle chamber, it must be opened when it is too high). If you want to open the main gate valve, you should first open the bypass globe valve, reduce the pressure in the middle chamber.

 (3) Special pressure relief valve can be installed outside the valve

A pressure relief valve can be set outside the middle chamber of the gate valve to control the pressure range. Set the discharge pressure of the pressure relief valve as the rated working pressure of the main valve. If the middle chamber is overpressured, it will automatically discharge to the set pressure, so as to maintain the safe operation of the main gate valve.