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A pressure reducing valve is the equivalent of an “automatic gear”. It can adjust its opening degree on its own depending on the conditions, ensuring that regardless of how the inlet pressure fluctuates, the outlet pressure remains stable at the value you have set. Its working principle is essentially an “eternal tug-of-war”. 01 Core structure: Three main components. Please take a look at this cross-sectional view; there are three key components inside the pressure relief valve, which together form an automatic balancing system: The spring – This is the component that responds to your commands, and it is located in the top cover of the valve. When you turn the screw at the top, you are compressing this spring. The force exerted by the spring downward represents the target pressure you have set. Diaphragm/Piston – The sensitive ear: located beneath the spring, resembling a membrane or a disc. Its lower surface is in direct contact with the outlet fluid. It is responsible for sensing the actual pressure at the outlet. Valve Plug – Actor: Connected below the diaphragm and seated in the middle of the flow channel. It moves up and down, which determines whether the valve opening is enlarged (resulting in higher flow rate and increased pressure) or reduced (resulting in lower flow rate and decreased pressure). 02 Tug of War: How does it \"move\"? The operation of a pressure relief valve is a struggle between the \"downward spring force\" and the \"upward outlet pressure\". Phase 1: Startup (spring dominance). At the beginning, there is no pressure at the outlet. The spring (as per your command) has great force, pushing the diaphragm and valve core firmly downward. Result: The valve is fully open. The high-pressure fluid rushed past with a roaring sound, filling the pipes downstream. Phase 2: Balance (parity). As the fluid flows past, the outlet pressure (downstream pressure) begins to increase. This pressure pushes up against the diaphragm. When the upward pressure equals the downward spring force, the valve spool stops in a semi-open, semi-closed position. Result: At this point, the outlet pressure is exactly stable at the value you set. Stage 3: Automatic adjustment (dynamic balance) – this is the most remarkable feature of pressure relief valves. Suppose someone downstream suddenly turns down the faucet (reducing water flow): the fluid flowing out can no longer move, and the pressure rises instantly. The diaphragm experiences high pressure and is pushed upward violently. The diaphragm moves the valve core upward, reducing the size of the valve opening. As less fluid enters, the outlet pressure naturally drops back down. The reverse is also true: if the water demand downstream increases significantly and the pressure drops, the spring will push the valve core downward, widening the valve opening to restore pressure. Note: The pressure relief valve is like a \"goalkeeper with its own pressure gauge\": by tightening the spring, you are telling it, \"Keep a pressure of 3 kilograms!\" ” If the downstream pressure is less than 3 kilograms, he opens the valve wider to let water flow through. If the downstream pressure is greater than 3 kilograms, he closes the door a little tighter to block the water. He fine-tunes the gate at all times based on feedback from downstream, so you don’t need to worry about it at all.