Pressure Reducing Valve vs Safety Valve vs Relief Valve: Key Difference

Control Valve is essential in water systems, steam lines, compressed air networks, boilers, pressure vessels, HVAC systems, chemical processing, and industrial pipelines. Excessive pressure can damage equipment, seals, flanges, instruments, and pipework. Insufficient pressure can reduce flow performance, disturb process stability, and affect system efficiency.

Pressure reducing valves, safety valves, relief valves, and pressure regulating valves all belong to the pressure valve category. Correct valve selection depends on the medium, pressure range, operating condition, installation position, and required safety function.

Main Function

A relief valve is used to release excessive pressure when pressure rises above a preset value. It is often associated with liquid systems. When pressure increases, the valve opens and allows part of the fluid to discharge through a bypass, tank return, or safe outlet path.

Typically relief valves open more slowly than most safety valves. Relief valves are generally suited for use with incompressible fluids such as water, oil and hydraulic fluids.

Relief Valve vs Safety Valve

A Safety Valve is typically used for relieving steam, gas or vapour and open suddenly. Relief Valves are typically used for relieving liquids and open slowly. Although Relief Valves are commonly referred to as Pressure Relief Valves in many industries and standards, there is a distinction in practical application between Safety Valves and Relief Valves.

Selection should not rely only on the valve name. Medium type, set pressure, flow capacity, back pressure, discharge path, temperature, and applicable standard must be considered.

Define the Required Function

When attempting to drop high pressure to lower constant pressure, one would use a pressure reducing valve. Safety valves are used to prevent damage to equipment from overpressuring. Relief valves are used to slowly discharge liquid from a system that may be experiencing overpressure. A pressure regulating valve would be used to maintain constant pressure in either the upstream or the downstream portion of a system within a given range.

Check Medium and Working Conditions

Valve selection should consider medium type, temperature, viscosity, corrosion level, pressure rating, flow rate, connection type, installation position, leakage class, and maintenance access. Steam, water, compressed air, oil, gas, and corrosive liquids all require different materials, seals, trim designs, and testing requirements.

Consider Standards and System Safety

Safety relief valves should be sized for their potential overpressure scenarios not just for normal operation. Incorrectly sizing a safety relief valve can result in an insufficient capacity, cause the valve to chatter, leak or not operate stably. When selecting a pressure reducing or regulating valve it is important to ensure that it will provide adequate control performance, be within the desired pressure boundaries, and provide satisfactory long-term operation.

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