Introduction
A pressure relief valve, also known as a safety valve, is a device that serves to automatically protect a pressure vessel, system or equipment from potential overpressure. Pressure relief valves are most commonly used for controlling the pressure in steam, water, air and gas systems. Traditional pressure relief valves are effective in controlling or limiting the maximum pressure in a system or vessel, but could be challenged in accurately controlling a process operating over a wide range of pressures. Pressure relief valves need to operate reliably during emergency overpressure conditions and prevent process fluid or gas from escaping into the environment.
Operating Principles
Pressure relief valves work based on an overpressure condition that is created within the system it protects. When pressure in the system increases, the force exerted by the system pushes or seats the pressure relief valve open, allowing process fluid to flow out of the system at a controlled rate. When the pressure in the system decreases, the pressure relief valve seats closed and prevents any further flow. The valve remains partly opened under precise conditions to maintain a constant pressure in the system.
Types of Pressure Relief Valves
There are several types of pressure relief valves used in industrial and commercial applications; each type is designed to meet the specific needs of a given application. The most commonly used types of pressure relief valves are:
· Spring-loaded relief valves: these valves use a spring-loaded mechanism to actuate the valve, typically with a pop-action design (also known as a snap relief valve). This type of valve is used primarily in applications where relatively high set pressures are required.
· Pilot-operated relief valves: these valves use a pilot valve with a diaphragm to sense the pressure and operate directly on the main valve. This type of relief valve is used in applications where precise pressure control is required.
· Self-operated relief valves: these valves use a diaphragm or a mechanical actuator that is actuated directly by the pressure in the system, without the need for an external source. This type of relief valve is used in applications where a wide range of set pressures is required.
· Ohm-operated relief valves: these valves are actuated by a current signal from an external power source, allowing for precise control of the set pressure. This type of relief valve is used in applications where a wide range of set pressures is required, but extreme accuracy and repeatability are not required.
Selection of a Pressure Relief Valve
When selecting a pressure relief valve, there are several criteria that need to be considered. These include: the type of fluid being controlled, the maximum pressure, temperature, set pressure, body material, valve size, port size, and the characteristics of the operating system. The type of relief valve selected should be based on the specific application requirements, such as the type of service the system will be used for, the capacity of the system, and the relief valves flow coefficient and characteristics.
Conclusion
Pressure relief valves are designed to protect a pressure vessel, system or equipment from potential overpressure conditions. There are several types of pressure relief valves, each designed to meet the specific needs of a given application. When selecting a pressure relief valve, there are several critical criteria that need to be considered, such as the type of fluid, maximum and set pressure, temperature, body material, valve size, port size, and the characteristics of the operating system. By carefully selecting the appropriate pressure relief valve for a given application, the risk of equipment damage or personal injury due to overpressure can be significantly reduced.
