What is the Difference Between Relief Valve and Safety Valve?

The difference between a relief valve and a safety valve is that safety valves act like emergency hatches for pressure systems. They slam open to release pressure if things get too intense, often shutting down the system entirely. Relief valves are more like pressure regulators. They open gradually to keep things from getting out of hand, allowing the system to keep running smoothly.

What is a Relief Valve?

Imagine a pressure cooker. A relief valve acts like its own safety whistle. It’s a small valve in a system that stays shut during normal use. But if pressure builds too high, the valve pops open, releasing pressure and preventing dangerous explosions. Relief valves are found in many machines, from car engines to water heaters, keeping them safe by preventing pressure buildups that could cause damage or injury. This table lists important technical terms related to relief valves, including their definitions and distinctions between different types of relief valves used in various services and pressure conditions.

Term	Definition
Pressure relief valve (PRV)	A valve controls or limits pressure in a system, designed to open at a predetermined set pressure to protect equipment from exceeding design limits.
Pressure safety valve (PSV)	A type of PRV with a manual lever for emergency activation; typically spring-operated, but may use a diaphragm at lower pressures.
Relief valve (RV)	Used in liquid service, opens proportionally as pressure increases to overcome spring pressure.
Safety valve (SV)	Used in gas service, typically full lift or snap-acting, popping completely open.
Safety relief valve (SRV)	A relief valve usable for gas or liquid service, with set pressure usually accurate for one fluid type at a time.
Pilot-operated relief valve (POSRV, PORV, POPRV)	Relieves by remote command from a pilot valve connected to upstream system pressure.
Low-pressure safety valve (LPSV)	An automatic system relieving by static pressure of gas; relieving pressure is small and near atmospheric pressure.

What is a Safety Valve?

Think of a safety valve as a system’s last line of defense. It’s a pressure-release hatch that stays sealed during normal operation. If pressure builds beyond a safe limit, the valve pops open, venting excess and preventing catastrophic events like explosions or fires. You’ll find safety valves in boilers, pipelines, and even your car’s engine. They act as fail-safes, automatically releasing pressure to keep things from going boom. This table lists important technical terms related to Safety Valves, including their definitions and distinctions between different types of safety valves used in various services and pressure conditions.

Term	Definition
Overpressure	Excess pressure over the set pressure of the safety valve.
Operating pressure	The pressure at which the system works under normal operating conditions.
Set pressure	The pressure at which the safety valve’s disc begins to lift and open.
Lift	The distance that the disc moves from the closed position to the position required for discharge.
Backpressure	The pressure is built upon the outlet of the safety valve during flow.
Built-up back pressure	The pressure at the outlet when the safety valve opens.
Superimposed backpressure	The pressure at the outlet of a closed safety valve.
Maximum allowable working pressure (MAWP)	The maximum allowable pressure at a designated temperature under normal operating conditions.

What is the Difference between Relief Valve and Safety Valve

Relief valves and safety valves serve very important roles in controlling pressure within systems. Relief valves are typically designed to protect equipment from damage due to overpressure by releasing excess pressure, while safety valves are specifically engineered to prevent catastrophic failures and ensure personnel safety in potentially hazardous situations. This table lists the main differences between relief valves and safety valves, focusing on their purpose, function, operation, system impact, and use case.

Feature	Pressure Relief Valve	Safety Valve
Common Use	Systems with static or continuous pressure	Thermal systems, vessels with stored energy
Adjustment	Typically automatic; opens to release pressure	Can be automatic or may require operator intervention
Capacity	Handles low pressures; continuous operation	Handles overpressure situations
Design	Materials withstand high temperatures, corrosion	Similar materials, withstand high temperatures, corrosion-resistant
Types	Mechanical, electric, electronic	Mechanical, electric, electronic
Rated Pressure Capacity	Should exceed rated pressure by at least 110%	Should exceed rated pressure by at least 110%
Closure and Plunger Guidance	Effective guidance to prevent issues with expansion, contraction, and grease buildup	Effective guidance to prevent issues with expansion, contraction, and grease buildup
Operating Temperature Range	Capable of operating above temperature limits	Capable of operating above temperature limits
Manual Lever for Opening	May or may not have a manual lever	Preferable to have a manual lever for opening, designed not to affect operation

Application of Relief Valve and Safety Valve in Real Life

Relief valves are commonly employed in various industries to regulate pressure within systems, preventing damage caused by overpressure. Safety valves, on the other hand, are important in applications where human safety is crucial, ensuring that pressure does not exceed safe limits to prevent accidents and equipment failures. Additional applications of relief valves and safety valves in real life are stated below:

• A relief valve prevents explosions by venting excess steam. 
• A safety valve stops the heater if the water pressure gets too high. 
• A relief valve releases pressure to avoid tank rupture. 
• A relief valve stops over-pressurization during inactive periods. 
• A pressure relief valve prevents overheating and engine damage. 

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