What is the working mechanism of a pressure relief valve? What are the different types, and in what situations are they used?

The steam pressure reducing valve ZZYP-16B is a self-acting pressure control valve that does not require any external energy source. It uses the energy of the medium being regulated as its power source; an actuator is used to control the position of the valve core, thereby changing the pressure difference and flow rate between the two ends and maintaining stable pressure before (or after) the valve. It features rapid response, good sealing performance, and low fluctuation in pressure set points, and is widely used in the automatic control of pressure reduction, stabilization, or relief for gas, liquid, and steam media. The products are available in three configurations: single-seat (ZZYP), sleeve type (ZZYM), and double-seat (ZZYN) ； The actuating mechanisms come in diaphragm type and piston type ； The operating modes include pressure regulation after the pressure relief valve (Type B) and pressure regulation before the pressure relief valve (Type K). The nominal pressure classes of the product are PN16, 40, 64 ； Valve body diameter range: DN20～300 ； The leakage level categories are II, IV, and VI ； The flow characteristic is quick opening ； The pressure can be adjusted in steps from 15 to 2500 Kpa. They can be combined as needed to meet the user’s operational requirements. There are many types of pressure regulators; common ones include pilot-operated piston pressure regulators, diaphragm pressure regulators, bellows-type pressure regulators, proportional pressure regulators, self-acting pressure regulators, directly-acting piston pressure regulators, backpressure control valves, and so on. They are suitable for different working media respectively. Different forms have different specific working principles. But the basic principle remains the same: a pressure relief valve reduces the inlet pressure to a desired outlet pressure by throttling through a control element, thereby maintaining a stable outlet pressure. However, general pressure relief valves require that the pressure difference between the inlet and outlet be ≥0.2 Mpa.

Throttling for pressure reduction is generally used in front of valves or measuring devices that have specific pressure requirements

Below are the materials I found and compiled from Haichuan before; in fact, the original poster only needs to search on Haichuan to find almost all the knowledge related to chemistry! A pressure relief valve is an automatic valve and a type of control valve. It is a valve that reduces the inlet pressure to a desired outlet pressure by throttling through a control element, and it is able to maintain a relatively constant outlet pressure despite changes in inlet pressure and flow rate, by utilizing the energy of the medium itself. Based on their operating principle, pressure relief valves are divided into directly-acting pressure relief valves and pilot-operated pressure relief valves. A direct-acting pressure relief valve uses changes in outlet pressure to directly control the movement of the valve disc. Diaphragm direct-acting pressure regulators are suitable for low-pressure, medium and small-diameter steam applications, while diaphragm membrane direct-acting pressure regulators are suitable for medium and low-pressure, medium and small-diameter air and water applications. A pilot-operated pressure reducing valve consists of a pilot valve and a main valve; changes in the outlet pressure are amplified through the pilot valve to control the movement of the main valve’s disc. Pilot piston type pressure reducing valve, suitable for steam, air, and water media at various pressures, sizes, and temperatures. If made of stainless acid-resistant steel, it can be used in various corrosive media. Pilot-operated bellows type pressure reducing valve, suitable for low-pressure, medium and small diameter media such as steam, air or water. The pilot diaphragm type pressure reducing valve is suitable for medium and low pressures, as well as for media such as steam or water with small to medium diameters. The fluctuation of the inlet pressure of the pressure reducing valve should be kept within 80% to 105% of the specified inlet pressure value; if it exceeds this range, the performance of the pressure reducing valve will be affected. 1. Generally, the pressure P2 behind the pressure relief valve should be less than 0.5 times the pressure in front of the valve, that is, P2