All About the Relief Valve

The popularity and importance of the valve are known to us. Actually, it does great favors to industrial process and daily life. A relief valve is particularly used to control or to limit the pressure in a system or vessel which can build up by a process upset, instrument or equipment failure, or fire. The word “relief” can explain all, I suppose.

From the definition, we may infer that it is designed or set to open at a predetermined set pressure to protect pressure vessels and other equipment from being subjected to pressures that exceed their designed limits. In most countries, it is legally required. But it should be mentioned that the use of the relief should keep to the equipments design codes provided by the American Society of Mechanical Engineers and American Petroleum Institute and such standards.

Generally speaking, the relief valve transforms to be as a path of least resistance when the set pressure is exceeded. It is forced to open to divert the fluid flow through the auxiliary route. For the fluid, it would be liquid, gas or liquid-gas mixture. When the fluid is diverted, the set pressure would drop to a normal level, while the relief valve closes at that moment. Take the high-pressure gas systems for example. The outlet of the relief valve is the open air which is connected to the piping. At this situation, it means that set pressure is lower that the relief valve and the relief valve only works with an area which is much smaller than that of the openings area of the valve. In some other cases, it is used to return all or part of the fluid discharged by a pump or gas compressor back to either a storage reservoir or the inlet of the pump or gas compressor. By doing this can protect the pump or the compressor and any associated equipment from excessive pressure. What else, it is employed to open at a predetermined low pressure limit and to admit air or an inert gas into the equipment so as control the amount of vacuum.

While putting into practical use, there are various specific kinds. They are pressure safety valve, safety relief valve, pilot-operated relief valve, low pressure safety valve, vacuum pressure safety valve and low and vacuum pressure safety valve. They are popular in their specified fields holding their own specifications. With the advancing modern industry, it would be employed in much more fields in the future.