Factors Affecting the Stability of the Pressure Reducing Valve |
1. Working Principle of Domestic Pressure Reducing Valves The operation of a domestic pressure reducing valve begins with the pilot valve, which is controlled by an adjusting bolt located at the top. When this bolt is turned clockwise, it compresses the spring, causing the diaphragm to move downward and push the connecting rod, thereby opening the pilot valve. Once the pilot valve opens, steam from the upstream inlet (section a) flows through the α channel (supply steam regulating passage), enters the annular steam chamber of the pilot valve, and is directed into the upper chamber of the main piston via the β channel. As steam continues to fill this chamber, the pressure increases, pushing the piston down and opening the main valve. This allows continuous flow of steam from section a to section b. When the downstream pressure in section b reaches the required level, any excess steam causes the pressure to rise further. This increased pressure is fed back to the lower chamber of the pilot diaphragm through the γ channel (pressure sensing channel). The diaphragm then moves upward, overcoming the force of the upper spring, and closes the pilot valve. This action stops the steam supply from section a, allowing the main valve to close under the influence of the return spring. As the pressure in section b drops, the cycle repeats, maintaining stable regulation. 2. Working Principle of Imported Pressure Reducing Valves In imported pressure reducing valves, the process is similar but with slight differences in design. When the pilot valve opens, steam from the upstream pipe (section a) passes through the internal filter and enters the a channel (supply steam regulating passage). Once the a channel is filled, some of the steam is directed to the b channel (pressure control channel), while the rest is sent to the lower chamber of the main diaphragm. The continuous steam supply pushes the main diaphragm upward, creating a force that lifts the main valve stem and opens the main valve. Steam then flows from section a to section b. When the downstream pressure in section b rises beyond the set point, the excess pressure is transmitted to the lower chamber of the pilot diaphragm via the c channel (pressure sensing channel). This causes the pilot diaphragm to move upward, closing the pilot valve and cutting off the steam supply from section a. As the pressure in the lower chamber of the main diaphragm decreases, the return spring forces the main valve to close, stopping the steam flow and allowing the pressure in section b to drop. This cycle ensures consistent pressure regulation. 3. Analysis of Condensed Water Damage and Its Impact on Regulation One critical issue affecting the stability of pressure reducing valves is the presence of condensed water in key components. When condensate enters the cylinder or the annular steam chamber, it can cause serious problems. Since water is incompressible, it prevents the main valve from closing properly. The return spring loses its effectiveness, and the piston cannot move, leading to uncontrolled steam flow from the inlet (section a) to the outlet (section b). If condensate fills the a and b channels as well as the lower chamber of the main diaphragm, the system becomes unstable. The steam pressure in the a cavity pushes the diaphragm upward, but the presence of water prevents the spring from returning the main valve to its seat. As a result, the main valve remains open, and the proportional control function is lost. Even though pressure reducing valves are designed to act as proportional regulators, the presence of condensate disrupts their normal operation. Friction between moving parts and the sequence of actions—where the pilot valve reacts first and the main valve follows—can introduce hysteresis. The delay in the main valve's response can lead to overpressure situations. Additionally, once condensate enters the system, it becomes difficult for the piston and diaphragm to move, making it nearly impossible to restore proper regulation. Understanding these factors is essential for maintaining the stability and reliability of pressure reducing valves in industrial applications. Regular maintenance and proper drainage systems are crucial to prevent condensate buildup and ensure smooth operation. |
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