When a pressure relief valve (PRV) is opened, the following series of actions and phenomena will occur, depending on its application scenario (such as boilers, pressure vessels, pipeline systems, etc.)
1. Basic functions of pressure relief valves
The pressure relief valve is a safety device that automatically opens when the system pressure exceeds the set value to release excess fluid (gas or liquid) to prevent equipment damage or explosion due to overpressure.
2. Specific phenomena that occur when it is opened
(1) Fluid discharge
Gas discharge: If the system contains gas (such as steam, air), the pressure relief valve will discharge the gas until the pressure drops below the set value.
Liquid discharge: If the system contains liquid (such as water, oil), the liquid may be discharged in the form of a jet or drip.
Two-phase flow: In some cases (such as steam boilers), steam and liquid water may be discharged at the same time.
(2) Sound and vibration
Sharp whistling sound: High-frequency noise is generated when high-speed gas or liquid flows through the valve port.
Equipment vibration: The discharged fluid may cause vibration of the pipeline or equipment.
(3) Pressure drop
The system pressure will drop rapidly until the pressure relief valve closes (when the pressure is lower than the set value).
(4) Safety chain reaction (optional)
Alarm triggering: The opening of the pressure relief valve may trigger the pressure alarm system to notify the operator.
Automatic shutdown: Some systems will automatically shut down equipment (such as boiler shutdown) due to the action of the pressure relief valve.
Record events: Modern systems may record data such as the action time and duration of the pressure relief valve.
3. Recovery process after opening
The pressure drops below the set value: The pressure relief valve will automatically close and stop discharging.
System re-establishes pressure: If the system continues to operate, the pressure will gradually return to the normal operating range.
Manual inspection: The operator needs to check whether the pressure relief valve has malfunctioned due to a fault or whether there are other problems in the system.
4. Types and effects of pressure relief valves
Spring-type pressure relief valve: Controls the opening pressure through spring force, acts quickly, and is suitable for gas and liquid.
Pilot-operated pressure relief valve: Controls the opening of the main valve through a pilot valve, and is suitable for high-pressure or large-flow systems.
Safety valve vs. pressure relief valve
Safety valve: usually used to prevent overpressure, needs to be manually reset after actuation.
Pressure relief valve: used for continuous or frequent pressure regulation, automatically reset after actuation.
5. Potential risks and precautions
Misoperation: If the pressure relief valve is frequently actuated due to a fault or improper commissioning, it may cause fluid waste or environmental pollution.
Corrosion or blockage: Long-term discharge of corrosive fluids may cause valve damage, or impurities in the medium may block the valve port.
Regulatory requirements: The discharge of the pressure relief valve must comply with local environmental regulations (such as discharge height, flow limit, etc.).
6. Application scenario examples
Boiler system: When the steam pressure exceeds the set value, the pressure relief valve discharges steam to prevent the boiler from exploding.
Chemical pipeline: During the chemical reaction process, the pressure relief valve protects the pipeline from overpressure.
Hydraulic system: In hydraulic equipment, the pressure relief valve prevents excessive oil pressure from damaging the seal.
