What is the difference between a relief valve and a control valve? Here, Fluid Controls explains the difference between the two components, explaining the features, safety information and benefits of each.
Pressure Relief Valves (PRV) were first used on steam boilers during the industrial revolution. Early boilers without them were prone to accidental Explosion due to their lack of safety features. A pressure relief valve is a static device that can reduce pressure even if there is no flow coming out of the reservoir. They are designed to open proportionally to increasing pressure and therefore are not recommended for applications requiring immediate full valve flow at set pressure.
The full flow of the relief valve is defined at 10% over set pressure and the two general types of protection encountered in industry are thermal protection and flow protection. These precision valves are designed for pressure gas systems, cryogenic systems, petrochemical applications and other special systems. The pressure relief valve features are designed to EN ISO 4126-1 standard, they have a lower whole life time cost and they optimise outlet flow for faster relieving. These valves usually release in to the drain or environment meaning that the steam or fluid that goes into the pressure release valve is naturally lost to the system.
A Pressure Control Valve (PCV) on the other hand, acts to change resistance to the flow of the fluid, but does not alter its destination. Fluid that passes through Pressure Control Valve is still going to the destination it was proposed for and is not lost. These valves are found in virtually every hydraulic system, and they assist in a variety of functions, from keeping system pressures safely below a desired upper limit to maintaining a set pressure in part of a circuit. The pressure control valve features guarantee performance of the system and optimisation of energy usage. Exact and precise control of differential pressures eliminates overflows at partial conditions and controls the temperature at low load conditions.
The difference between PRV and PCV is that the PCV is called as first line defence which is meant for primary safety. The PRV is not used as a pressure control device but as a backup of last resort. Pressure Control Valves are ideal for applications requiring a reduced pressure to a cylinder whereas Pressure Relief Valves are used to maintain a pre-set downstream pressure.
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