Pressure relief valves are essential components in fluid systems, designed to protect equipment and pipelines from overpressure. Accurately identifying the symbol for a pressure relief valve in technical diagrams—such as P&ID, schematic, or ISO layouts—is crucial for engineers, technicians, and maintenance personnel. This article explains the most common pressure relief valve symbols and how they appear across different engineering standards.
What Is a Pressure Relief Valve?
A pressure relief valve (PRV), sometimes simply called a relief valve, automatically opens to release excess pressure when the system exceeds a set threshold. It then reseats to allow normal operation. These valves are used in industries such as oil and gas, HVAC, water treatment, hydraulics, and manufacturing.
Common Pressure Relief Valve Symbols
1. Symbol for Pressure Relief Valve in P&ID
In a P&ID (Piping and Instrumentation Diagram), the pressure relief valve symbol is usually a combination of a valve body and a spring-loaded actuator. The basic form includes:
/\
---| |--- (Indicates valve)
|| (Vertical line with arrow or spring denotes relief function)Or simplified as:
-->┤┐ (Arrow into a box with an angled outlet)Annotations like “PRV” or “RV” may accompany the symbol.
2. Relief Valve Symbol in Schematics
In hydraulic or pneumatic schematics, the symbol of a pressure relief valve typically features:
- A square or rectangle with a spring
- A directional arrow pointing away from the pressure source
- A dashed pilot line (for pilot-operated valves)
ISO 1219 compliant version:
┌────┐
|↖-->| (Arrow + adjustable spring + flow path)
└────┘Alternative Terms and Variations
- Symbol of Pressure Relief Valve and Relief Valve Symbol: Used interchangeably in most industries.
- Symbol of Relief Valve: May refer to either pressure or vacuum relief types depending on context.
- Pressure Control Valve Symbols: A broader category, which includes pressure relief valves, pressure reducing valves, and sequence valves. Each has distinct symbols.
Pressure Relief Valve Schematic Symbol Examples
Depending on the system, the schematic symbol may show:
- Pilot line: For pilot-operated pressure relief valves
- Adjustable spring: Indicating the valve set pressure can be changed
- Tank return line: In hydraulic diagrams, showing fluid discharge to reservoir
Best Practices for Reading Valve Symbols
- Always look for arrow direction to understand flow path
- Identify spring and adjustment markers
- Use legend or key provided in the diagram for non-standard symbols
- Match symbol type to system (hydraulic, pneumatic, process piping)
Conclusion
Understanding the symbol for pressure relief valve is key to reading engineering diagrams correctly. Whether it’s labeled as a relief valve symbol, pressure control valve symbol, or pressure relief schematic symbol, these symbols convey important safety functions in fluid systems. Use this guide to recognize and interpret them accurately across P&ID, ISO, and schematic diagrams.
Need help choosing or identifying the right pressure relief valve for your system? Contact us for expert support and reliable valve solutions.
