A pressure relief valve (PRV) is a device that releases the gas or vapour from gases at regular intervals.
These valves are generally used to regulate the flow of gas between two containers, such as keeping the pressure consistent in storage containers and ensuring equal distribution throughout the system. A pressure relief valve is a safety valve fitted to protect pressure vessels from failure or explosion when the units attain pressure spikes above the maximum allowable working pressure. A pressure release valve is a safety device designed to regulate system pressure when pressurised fluid or compressed air systems hit a predetermined set point. Safety valves release excess pressure in cases of an overpressure event preventing system failure due to high pressure.
Pressure relief valves can be either manual or automatic. The manual ones actually require somebody to turn them on. When the predetermined system pressure is reached, an experienced operator manually opens the pressure safety valve. Once the desired pressure is attained, they closes the valve.
The automatic types do so automatically when they sense excess pressure inside their chamber. As soon as the maximum set pressure is reached, an automatic pressure safety valve will activate an opening mechanism that allows bubbles to escape into their surroundings rather than build up within the pressure vessel. Since most pressure relief valves need air/gas/liquid to function properly, they cannot be installed in vacuum-sealed systems.There are two main types of pressure relief valves: burst disc types and safety relief valve types.
A burst disc safety valve has a hollow cylindrical covering over the piping system that ruptures when excessive pressure builds up inside it. The disc lifts automatically, which then lets out excess gas or vapour into its surroundings.
On the other hand, a safety valve is a pressure relief valve characterised by fuses made from non-conductive materials (e.g., ceramic) to accomplish their task. Once these fuse wires melt due to high liquid or compressed air pressure, they activate an opening mechanism that helps release excess gas back into containers/systems where they belong. The valve opening mechanism works to enable the safety valve to have a gradual lift generally proportional to the pressure rise inside the pressurised vessel. These safety valves are commonly found in liquid or compressible fluid systems.
Pressure relief valves have a wide variety of applications, mainly because gases and liquids need to be transported from one place to another by companies in a number of industries. Some common uses include: ensuring safe storage and transportation of flammable gases (i.e., propane) powering pneumatic equipment ensuring proper operation of pressure regulators transporting fuels (e.g., gasoline) for vehicles or power generators running compressors within appliances like refrigerators, freezers, ACs, etc. supplying contents to aerosol spray cans preventing the sudden build-up in gas lines that could lead to explosions. These devices can be used either individually or in conjunction with other products (e.g., a safety relief valve with a pressure regulator) to ensure that systems remain safe and effective.
Pressure relief valves are used in a variety of industries. Some common examples include:
PRVs are used in aerospace applications to allow gases to escape when they come in contact with aircraft that fly at high altitudes. This is mainly because the air is very thin at high altitudes, which results in excess pressure build-up inside gas containers.
These valves are used to allow gaseous products to escape into the atmosphere when they come in contact with pipelines. Also, refineries need these devices to release gases that would otherwise become volatile under extreme conditions inside a pressurised system.
PRVs are important for cars since they keep fuel vapours from collecting within tanks and then exploding due to excessive internal pressure. Likewise, aerosol sprays need relief valves of their own so as not to blow up inside canisters due to increasing internal pressures. Some construction equipment uses pneumatic engines that require a constant flow of pressurised air or gas in order to lift or move heavy construction materials like precast concrete slabs.
Since gases are often unstable, it's important for them to be conducted properly not to explode or pollute the environment. This is why pressure relief valves are often installed between chemical processes associated with generating polymers, petroleum refining, wastewater treatment, etc.
At home, a pressure relief valve would most likely be found on things like air compressors, aerosol spray cans, etc. A typical example is a bicycle tyre pump: when you pressurise the device's chamber with your hand and then release it quickly, the excess air/gas that was built up escapes from its opening.
A vacuum relief valve works opposite that of a pressure relief valve. In the rapid emptying of tanks or fluid flow, chances of vacuum build-up are very high. In such circumstances, a vacuum pressure relief device opens to let in atmospheric pressure. As the atmospheric pressure rises inside the pressurised system, it cancels out the excessive internal vacuum preventing catastrophic equipment failure.
Certain types of relief valves use spring pressure to counteract the system pressure. The opening pressure (cracking pressure) coming from the system must exceed the spring force. When this condition is met, the valve opens, relieving pressure in the equipment or system. This is the basic mechanism for a low lift safety valve or a full lift safety valve, with certain operational differences between the two.
Bursting pressure refers to the maximum allowable internal pressure for something like an air tank or aerosol can without experiencing permanent damage (i.e., leakage). For example, the burst-pressure rating of your average aerosol spray can is around 300 psi (pounds per square inch), which means that once the internal pressure reaches 300 psi, it will no longer be able to contain gas and instead release it into open spaces until its internal pressure drops below this threshold again. Another term used to describe a vessel's predetermined set pressure is "venting pressure."
On many valves, you will find a setting that allows you to adjust how quickly it opens so it can be tailored to your application. If you are putting a regulator on the valve, there are certain rules about what range of settings are safe with different regulators. These are outlined in the regulator manufacturer's documentation. Some manufacturers also provide a pressure vessel code when you purchase pressurised equipment.
The settings of your PRV can have a significant impact on how it functions and its safety margins. When choosing a pressure relief valve, certain guidelines need to be followed and some general rules about how many psi you can allow before opening up. In addition, you must take into consideration all sources of back pressure on your system - this may require special design considerations so as not to exceed those limits.