Pressure reducing valve works and selection
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The working principle of a pressure reducing valve is based on controlling the flow and pressure of compressed air to maintain a stable output. A direct-acting pressure reducing valve, as shown in Figure 14-1a, operates by allowing high-pressure air (P1) to enter through an orifice, which reduces the pressure to P2. The output pressure can be adjusted using a spring system, where turning the knob clockwise compresses the springs, increasing the opening of the valve and raising P2. Conversely, turning it counterclockwise decreases the opening, lowering P2.
If P1 increases suddenly, the diaphragm in chamber 6 experiences greater force, causing it to move upward. This allows some gas to escape through the overflow hole 12, reducing the pressure and closing the intake valve port 10 via the return spring. This action increases throttling, bringing P2 back to its set value. If P1 drops, the diaphragm moves down, opening the valve and reducing throttling, thus restoring P2.
When the knob is turned counterclockwise, the springs relax, allowing higher pressure to push the diaphragm up, closing the intake valve. This results in no output until the valve is reactivated. In summary, the relief valve regulates pressure through throttling, diaphragm force balance, and overflow mechanisms. To prevent environmental contamination from small gas leaks, a non-venting relief valve can be used instead.
For higher output pressures or larger diameters, a pilot-operated pressure reducing valve is more suitable. It uses a smaller, direct-acting valve to control the main valve, improving sensitivity and accuracy. Pilot valves can be internal or external, depending on where the small valve is mounted. These valves are ideal for large diameter systems, long distances, or hazardous environments.
A set-point regulator is a high-precision pressure setting device, commonly used in applications requiring accurate air or signal pressure, such as pneumatic laboratories. It consists of three main parts: a direct-acting valve, a constant pressure drop mechanism, and a nozzle-baffle system that amplifies pressure changes. This design allows for precise control and stability, even with minor fluctuations.
In operation, when the calibrator is inactive, compressed air is filtered and flows through the system, but no output occurs due to the closed main valve. When active, the handle is rotated, adjusting the baffle position to increase pressure in chamber G and D. This triggers the diaphragm movement, opening the main valve and allowing regulated output. Feedback mechanisms ensure that any input pressure variations are quickly compensated, maintaining stable output.
The basic performance of a pressure reducing valve includes the pressure regulation range, pressure characteristics, and flow characteristics. The pressure regulation range defines the adjustable output pressure, while pressure characteristics refer to how well the valve maintains output pressure despite input fluctuations. Flow characteristics describe the valve’s ability to keep output pressure stable as flow rate changes.
When selecting a pressure reducing valve, consider the required type, accuracy, and maximum flow rate. Ensure the valve’s operating pressure exceeds the desired output by at least 0.1 MPa. Install the valve after a filter or scrubber, and avoid reversing the inlet and outlet. Always loosen the knob when not in use to prevent diaphragm deformation and maintain optimal performance.