The difference between safety valves and pressure relief valves

I. The principle of a pressure relief valve is that when the pressure in the pipeline exceeds the set pressure of the valve, the oil flows out through it, thereby preventing the pressure in the pipeline from rising above a certain limit. The needle-type pressure relief valve regulates the clamping force by adjusting the length of the spring inside the valve. When the pressure in the pipeline exceeds the set value, the spring is compressed in the opposite direction, causing the sealing needle to open and allowing oil to leak out; this mechanism serves to protect the equipment and regulate the system pressure. II. In a broad sense, so-called safety valves include pressure relief valves. From the perspective of regulatory requirements, these are valves that must be installed directly on steam boilers or certain types of pressure vessels, and it is necessary for them to be approved by the technical supervision authorities. In a narrow sense, only those valves are referred to as safety valves; the others are generally called pressure relief valves. : III. Safety valves and pressure relief valves are very similar in structure and performance; both discharge the fluid inside automatically when the set pressure is exceeded, thereby ensuring the safety of the production equipment. Due to this inherent similarity, people often confuse the two when using them; furthermore, some manufacturing equipment also specifies that either one can be used. Therefore, the differences between the two are often overlooked. As a result, many problems have arisen. If a more precise definition for both is to be provided, it can be understood in accordance with the definition outlined in Part 1 of the ASME Boiler and Pressure Vessel Code: (l) Safety Valve – an automatic pressure relief device driven by the static pressure of the medium in front of the valve. It is characterized by a sudden, full-open starting action. Used for gas or steam applications. (2) Relief Valve, also known as a pressure relief valve, is an automatic pressure release device driven by the static pressure of the medium in front of the valve. It opens proportionally as the pressure exceeds the opening force. It is mainly used in fluid applications.

Why do I think a pressure relief valve is just a manual (or pneumatic) on-off valve? The safety valve activates automatically when overpressure is reached.

Safety valves are special types of equipment that require calibration; they open once they reach the set pressure. As for pressure relief valves, they can be simply considered to be pneumatic valves, with an internal mechanism that controls whether pressure is released or not

According to the API description, safety valves are primarily designed for compressible fluids, while pressure relief valves are mainly used for incompressible fluids; safety pressure relief valves are suitable for both types of fluids.

I’m also confused; I hope someone can provide an authoritative answer.

”A safety valve is a type of special equipment that requires calibration; it opens once the set pressure is reached~~~ A pressure relief valve, in simple terms, is essentially a pneumatic valve~~~ There is an indoor control mechanism to determine whether pressure relief should occur. I agree with this description!

The pressure relief valve is used only to control the system pressure; it reduces the pressure when the system is under overpressure, and it automatically returns to its closed state once the pressure is normal again； When the pressure in the safety valve system equipment exceeds the limit, the safety valve opens and the fluid flows out. As long as you do not carry out maintenance, it will continue to leak until you fix it ；

First of all, there are many types of safety valves, including fully open type and proportional type. Full opening means that the safety valve opens within a very narrow range in proportion to the pressure, and then opens completely ； A proportional safety valve opens in proportion to the pressure level, and a pressure relief valve should belong to the category of proportional safety valves