Functions of safety relief valves

A safety relief valve is a pressure valve and its main function is to pop open to avoid or eliminate chances of abnormally high pressure which exceed the predetermined levels. At the same time they smoothly and continuously modulate the fluid flow to prevent pressure from building up above a certain desired value. It is normally closed until the pressure levels approaches the said predetermined value when it pops open to relief off the system the building pressure. As system pressure rises, the safety relief valve will relief the flow through the output and when the pressure drops the valve then closes and starts running smoothly.

As safety devices they are also designed for fast action rather than for pressure modulation. Pressure is relieved by allowing the pressurized fluid to flow through an auxiliary passage out of the system. It protects pressure vessels and other equipments from damages or rupturing due to high pressures by opening and relieving the fluid as it reaches the predetermined pressure which is believed as undesired pressures. When the set pressure is acquired the relief valve then becomes the path of least resistance and the valve is forced to open and a portion of the fluid is diverted through the auxiliary path. This diverted fluid is usually routed by a piping system known as a relief header to a central gas flare where is usually burned and the resulting gases released to the atmosphere.

After the fluid is diverted the fluid pressure will then drop and this will lead to closing of the valve preventing any more diversion of the fluid to the auxiliary path. In some cases the relief valve has by-pass valves that are used to return all or part of the fluid discharged by the pump or compressor back to the storage reservoir or to the inlet of the pump or compressor. The bypass valve can either be internal or external.

System too have safety relief valves that protect them from being subjected to internal vacuum collapses; that is pressure going below a desired point especially lower than the equipments handling capacity. Here safety relief valves will open thus allowing air or inert gases into the system so as to control the amount of the vacuum and this will also increase pressure to the desired level as well. In most cases this happens when the tanks are being emptied or when being rinsed with cold water after a hot clean in place procedure has been applied. This might lead to condensation of the tank and might lead to collapsing, thus a safety relief valve plays a great role in preventing this.

Thus as we have seen, the safety relief valve relieves pressure on all fluids including water or gases, by automatically sensing the pressure rate and prevents it from reaching that undesired or harmful range. Even though pressure safety valves are almost similar to safety relief valves, one should not confuse between the two, in that, pressure safety valves have a manual lever to open the valve in case of emergency, but for the safety relief valves it is an automated system.