Differences between pressure relief valves, safety valves, pressure stabilizing valves, and pressure discharge valves

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The differences between pressure relief valves, safety valves, pressure stabilizing valves, and pressure discharge valves: All of these are types of pressure valves, and the differences lie mainly in their functions. A pressure reducing valve is a device that reduces a medium with high pressure to one with low pressure. Its characteristic is that it maintains the outlet pressure and temperature within a certain range, even when the inlet pressure keeps changing. A safety valve is a valve used to prevent equipment or pipelines such as boilers and pressure vessels from being damaged due to overpressure. When the pressure is slightly above the normal operating pressure, the safety valve opens automatically to reduce the pressure. When the pressure is slightly below the normal operating pressure, the safety valve closes automatically, stopping the flow of fluid and maintaining the seal. Pressure relief valves are primarily used in situations where pressure is too high; when the pressure exceeds the set value, the internal component of the valve is pushed open to release pressure promptly. Once the pressure drops, it returns to its original position. They are not very different from safety valves. Pressure relief valves are usually used with liquids, while safety valves are more often used with gases and steam. A pressure regulator is a device that maintains the medium in a certain area within a specific pressure range. Difference from a pressure reducing valve: A pressure reducing valve reduces the outlet pressure to a set value, regardless of how the inlet pressure changes, thereby serving to reduce pressure. Pressure regulator: Maintains a constant upstream pressure regardless of changes in downstream pressure and demand. Safety valves and pressure relief valves are two types of valves, which are specialized valves. Among them, the safety valve is a type of safety relief device and a specialized valve that operates only when the working pressure exceeds the allowable limit, thereby protecting the system. Pressure reducing valves are process valves that reduce the pressure of high-pressure streams to meet the pressure requirements of downstream systems; their operation is continuous. Table of design standards for pressure regulators. Standard code, Standard name: JIS B3372-1982 – Pressure regulators for compressed air; JIS B8410-1990 – Pressure regulators for water systems; GB/T 10868-1989 – Technical specifications for temperature and pressure regulators in power plants; GB/T 12244-1989 – General requirements for pressure regulators; GB/T 12245-1989 – Test methods for pressure regulators; GT/T 12246-1989 – Pilot-operated pressure regulators; GB/T 3656-1994 – Water pressure regulators; GB/T 3656-1994 – Air pressure regulators for ships; ASTM F1370-1992 – Pressure regulators for ship’s water supply systems; JB/T 53265-1994 – Quality grading of pilot-operated pressure regulators; AWWA C511-1992 – Pressure and backflow prevention valve assemblies. Working principle of pressure regulators: Serial number, Name, Working principle: 1. Direct-acting diaphragm pressure regulator – As the pressure on the outlet side increases, the diaphragm moves upward, reducing the valve opening, increasing the flow rate and thus the pressure drop. This leads to a decrease in the pressure behind the valve and a drop in the pressure on the outlet side. The membrane moves downward, the valve opening increases, the flow rate decreases, the pressure drop reduces, and the pressure behind the valve rises. The outlet pressure after the valve always remains at a constant pressure set by the setting adjustment screw. 2. When the pressure on the outlet side of the directly-acting bellows-type pressure regulator increases, the bellows move upward, the valve opening decreases, the flow rate increases, and the pressure drop grows; as a result, the pressure behind the valve decreases, and the pressure on the outlet side falls. The bellows move downward, the valve opening increases, the flow velocity decreases, the pressure drop reduces, and the pressure behind the valve rises. The outlet pressure after the valve always remains at a constant pressure set by the setting adjustment screw. In a 3-pilot piston-type pressure reducing valve, turning the adjustment screw pushes open the pilot valve disc; the fluid enters above the piston from the inlet side. Since the area of the piston is larger than that of the main valve disc, this pushes the piston downward, causing the main valve to open. The pressure behind the valve balances the force exerted by the adjustment spring, which in turn changes the opening degree of the pilot valve and thus alters the pressure above the piston, allowing control over the opening degree of the main valve disc and maintaining a constant pressure behind the valve. The working principle of the 4-pilot diaphragm pressure reducing valve is the same as above. The pressure in the upper chamber of the membrane is controlled by a bypass control valve. In a 5-pilot diaphragm pressure relief valve, when the adjusting spring is in its relaxed state, both the main valve and the pilot valve are closed. When the handwheel is turned clockwise, the pilot valve diaphragm pushes down on the pilot valve, allowing the fluid to flow past the pilot valve and above the main diaphragm; this in turn pushes the main valve open, enabling the fluid to flow toward the outlet. At the same time, the fluid enters below the pilot valve diaphragm, causing the outlet pressure to rise until it reaches equilibrium with the force exerted by the spring. When the outlet pressure increases, the pilot valve diaphragm moves upward, reducing the opening of the pilot valve. Meanwhile, when the flow rate of the medium beneath the main diaphragm decreases, the pressure drops, and the outlet pressure decreases until a new equilibrium is reached; the opposite occurs as well. 6 Modular pressure reducing valve: The pressure reducing valve consists of a main valve, a pilot valve, and a shut-off valve. When the adjustment spring is in a free state, the main valve and pilot valve are closed. By turning the adjustment screw, the medium pushes the pilot valve open; at the same time, it enters the rubber diaphragm chamber of the main valve, where its pressure balances that of the adjustment spring. This causes the rubber diaphragm to move upward, thereby opening the main valve and allowing the medium to flow toward the outlet (at this point, the stop valve is open to maintain a certain pressure in the chamber). The medium exiting the outlet then returns to the chamber above the rubber diaphragm and to the chamber below the pilot valve. When the outlet pressure increases, the diaphragm of the pilot valve moves upward, reducing the opening degree of the pilot valve; this causes the pressure of the medium in the chamber to decrease. Concurrently, as the chamber pressure drops, the rubber diaphragm of the main valve moves downward, decreasing the opening degree of the main valve and thus lowering the outlet pressure, until a new equilibrium is reached ； The same is true in reverse. 7 Lever-type pressure reducing valve: a pressure reducing valve in which the pressure is balanced by a weight on the lever. Its operating principle: When the lever is in its free state, the valve disc and valve seats with dual seats are in a closed position. Under the influence of inlet pressure, the valve disc is pushed upward, creating pressure at the outlet side; the counterweight on the lever is used to adjust the valve so that the desired outlet pressure is achieved. When the outlet pressure exceeds the set value, the pressure of the medium acting on the upper valve seat is greater than the force acting on the lower valve seat, creating a pressure difference that causes the valve disc to move downward, reducing the throttling area. As a result, the outlet pressure drops, reaching a new equilibrium ； The same is true in reverse. The structural principle of the 8-pilot diaphragm pressure regulator is the same as that of the pilot piston pressure regulator.