Role and Installation of Safety Valves in Pressure Vessel

 
Safety valves are the core safety devices in pressure vessel systems, primarily used to prevent system pressure from exceeding the allowable range and to ensure the safe operation of equipment. Their function is to maintain a seal under normal working pressure and to open automatically and rapidly when the pressure exceeds the set value, releasing excess medium. This effectively prevents dangerous incidents such as explosions and damage to pressure vessels. Once the system pressure returns to normal, the safety valve will automatically close, preventing the medium from continuing to discharge and ensuring the normal operation of the system.

The Role and Importance of Safety Valves

 
Safety valves have a direct impact not only on equipment and personal safety but are also closely related to energy conservation and environmental protection. The reliability and performance of safety valves directly determine whether equipment can be protected in time in the event of overpressure. To ensure the correct use of safety valves, it is crucial to select the appropriate type and specifications. When choosing a safety valve, the following points should be particularly noted:

1. Matching of Discharge Capacity

 
The rated discharge capacity of the safety valve must be greater than or equal to the safety discharge capacity of the container to ensure effective pressure release and prevent further increase in internal pressure when the pressure exceeds the standard.

2. Selection of Safety Valve Type

 
The commonly used safety valve is the direct spring-loaded type, which has a simple design and reliable operation. When using a pilot-operated safety valve, it should be ensured that even if the pilot valve fails, the main valve can still open automatically to discharge enough medium to ensure container safety.

3. Special Medium Requirements

 
For systems containing toxic, flammable, explosive, or polluting media, a closed-type safety valve must be used. This type of valve can prevent medium leakage into the atmosphere, reducing environmental pollution and safety hazards. If a lifting device is required, a closed safety valve with a handle should be selected to facilitate manual testing during safe operation.

4. High Pressure and High Temperature Applications

 
For steam safety valves with an opening pressure exceeding 3MPa or gas systems with a working medium temperature above 350°C, a safety valve with a radiator is recommended. The radiator can effectively prevent high-temperature media from directly corroding or damaging internal components such as springs, extending the service life of the valve.

5. Back Pressure and Corrosive Medium Conditions

 
In some working conditions, the system may be subject to back pressure or use highly corrosive media. In this case, a safety valve with a bellows should be selected. The bellows design can isolate the direct impact of the medium on internal components such as springs, preventing the valve from being affected by corrosion or excessive back pressure.

6. Regular Inspection and Lifting Mechanism

 
In some situations, it is necessary to regularly inspect safety valves, which should be equipped with a reliable lifting mechanism for maintenance and calibration. However, for safety valves handling toxic, flammable, or explosive media, a lifting mechanism is generally not recommended unless the user has special requirements, to avoid safety hazards caused by accidental opening during non-operation.

7. Selection of Opening Type

 
For applications with a large safety discharge capacity, a full-opening safety valve should be chosen. This type of valve can fully open when the pressure exceeds the set value, quickly discharging a large amount of medium. Conversely, for applications with a small discharge capacity or where pressure stability is required, a micro-opening safety valve should be selected to achieve more precise pressure control.

8. Sealing Surface Requirements

 
The sealing surface type of the safety valve should meet the performance requirements of the working conditions. A high-quality sealing surface design can effectively reduce leakage and ensure the reliability of the medium discharge and resealing process.

Installation Standards for Safety Valves

 
The correct installation of safety valves directly affects their protective functions. Compliant installation steps can not only ensure the normal operation of safety valves but also extend the service life of equipment. When installing safety valves, the following matters should be particularly noted.

1. Verification and Setting Pressure

 
Before installation, safety valves should be regularly verified by professionals according to the working environment and usage conditions, usually at least once a year. The set pressure of the safety valve should generally be set to 1.05 to 1.10 times the highest working pressure of the container, but should not exceed the design pressure (except for mobile pressure containers).

2. Vertical Installation Requirements

 
Safety valves must be installed vertically in the gas phase space above the liquid level of the pressure vessel, or connected to the gas phase space through pipelines. This installation method ensures that the safety valve can respond quickly and release pressure in a timely manner when the pressure exceeds the standard.

3. Connection Pipe Size

 
The cross-sectional area of the connection pipe between the safety valve and the pressure vessel must not be less than the inlet cross-sectional area of the safety valve. If multiple safety valves are installed on one connection, the area of the connection should be at least equal to the total area of the inlets of these safety valves to ensure that the medium can smoothly enter the safety valve through the pipeline.

4. Setting of Intermediate Cut-off Valves

 
It is not advisable to install intermediate cut-off valves between the safety valve and the pressure vessel. If the medium inside the container is flammable, toxic, or highly viscous, a cut-off valve can be installed for easy replacement and cleaning of the safety valve, but its diameter and structure must not affect the normal discharge function of the safety valve. During normal operation, the cut-off valve must be kept fully open and sealed with lead.

5. Emission Pipe Installation Requirements

 
Closed-type safety valves should be connected to an emission pipe to safely discharge gases outdoors or to other safe areas. The diameter of the emission pipe must not be less than the outlet diameter of the safety valve, and the emission pipe must have reliable support to prevent vibration or excessive additional stress on the container when the safety valve opens. In addition, the emission pipe should be designed with free expansion functions to cope with the thermal effects when high-temperature media expand. For flammable media, the emission pipe should also be equipped with grounding devices to prevent static accumulation from causing fires. If the emission pipe may accumulate condensate or rainwater, a drainage pipe should be set at the lowest point to discharge the accumulated liquid in time to avoid affecting the normal operation of the safety valve due to back pressure.

Conclusion

 
In summary, safety valves are indispensable key safety devices in pressure vessel systems, and their performance and reliability are directly related to the safe operation of equipment and personal safety. By correctly selecting the type, installing according to specifications, and regularly inspecting and maintaining, overpressure accidents can be effectively prevented, ensuring the smooth operation of the system under various conditions. Only by incorporating the design, installation, and management of safety valves into the entire lifecycle of equipment safety management can their protective role be fully utilized, ensuring efficient, safe production, and effective environmental protection.