**Abstract:**
This paper elaborates on the hydraulic principles and characteristics of full-hydraulic-controlled pressure regulating valves. It analyzes the calculation methods for transient processes and parameter settings when using such valves. During the operation of a hydropower station, when a sudden load rejection occurs, the governor automatically controls the turbine to quickly close the guide vanes, which leads to an increase in both pipeline pressure and unit speed. For power plants with long pressure diversion channels, adjusting the closing time of the guide vanes may not always ensure that both pressure and speed increases remain within acceptable limits. To address this issue, surge tanks or pressure regulating valves are commonly used to manage the conflict between pressure and speed rise, ensuring safe operation. However, installing surge tanks requires significant investment and construction time, and some stations face geographical constraints that make it difficult to build them. Therefore, small- and medium-sized hydropower stations benefit greatly from adopting pressure regulating valve systems.
The TFW-type pressure regulator, which features full-hydraulic control and a hydraulic linkage with the guide vane, is known for its safety, reliability, low cost, and short installation period. Since the 1980s, nearly 100 hydropower stations in China have eliminated surge tanks in favor of TFW-type hydraulic control valves, with no reported safety incidents. Hydropower stations like Zhejiang Jin Hang and Xuanping Creek have operated safely for many years. Even in developed countries such as Norway, large numbers of pressure regulating valves are used instead of surge tanks—examples include the TJΦRHM hydropower station, which has a rated head of 158 meters and a single capacity of 60 MW.
The hydraulic principle and characteristics of the pressure regulating valve are further explained below:
**1. Hydraulic Principle of Full-Hydraulic-Controlled Pressure Regulating Valve**
The basic movement of the TFW-type pressure regulating valve is “fast opening, slow closing.†It remains stationary for small load changes, opens during significant load rejection, and does not operate when the load increases. The modified governor’s main valve and pressure regulating valve system (as shown in Figure 1) operates entirely through pressure oil. The hydraulic process is as follows:
(1) When the unit load remains constant, the main pressure valve piston is in the “balance position,†allowing pressure oil to flow into the pressure regulating valve closing chamber via throttle A. The pressure regulator valve remains closed due to higher pressure than water thrust.
(2) When the unit reduces load (about 15% of rated output), the main pressure valve moves slightly, allowing only a small amount of pressure oil to enter the guide vane relay closing chamber. The pressure regulator valve still remains closed.
(3) During sudden large load rejection (over 15% of rated output), the main pressure valve displaces significantly, allowing a large volume of pressure oil to rapidly open the pressure regulator valve. This causes the guide vane to close quickly, with zero lag time.
(4) When the unit increases load, the main pressure valve moves downward, allowing pressure oil to enter the guide vane relay opening chamber. The pressure regulator valve remains closed.
(5) Two-stage guide vane closure is achieved by restricting flow through throttle C, allowing the pressure regulator valve to open quickly before the guide vane fully closes.
(6) In case of failure, the unit can be shut down slowly using a small amount of pressure oil from throttle A to prevent excessive pressure in the water supply pipe.
(7) Throttle functions include controlling slow-closing time, setting check valve opening pressure, and defining two-stage closure positions.
**2. Characteristics of the Pressure Regulating Valve**
Domestic pressure regulating valves are categorized into seven types based on diameter and head. They are mainly produced by Sichuan Jiajiang Hydraulic Machinery Factory and Chongqing Hydraulic Turbine Factory. Key parameters are listed in Table 1.
(1) Structural features: The TFW-type valve includes a guide vane energy dissipation shell, cone or circular valve plate, balance chamber, relay, guide oil chamber, piston stroke limit ring, and drain/fill valve. Its compact design allows easy integration with other components.
(2) Flow characteristics: Based on spool valve type and Yx/Dx values, flow curves can be drawn to determine pressure regulator performance.
(3) Operating characteristics: Minimum operating pressure ranges from 1.3 to 2.0 MPa, increasing with working head. Maximum operating pressure is generally 2.5 MPa.
(4) Layout considerations: The valve should be placed without increasing unit spacing, and must coordinate with the governor and inlet valve. Vertical units are typically placed in front of the volute, while horizontal units are installed before the turbine inlet valve.
**3. Transient Process in Power Plants with Pressure Regulating Valves**
Assuming linear relationships between turbine flow, valve opening, and time, the entire water diversion system shows linear flow changes. After installing the pressure regulator, the adjustment characteristics and flow-time changes are shown in Figure 2.
(1) Calculation criteria: Maximum pressure rise rate depends on rated head, and speed increase rate depends on unit capacity relative to total system capacity.
(2) Variables involved in calculations include Ts’ (full closing time), ζ (allowable pressure increase rate), QTM (flow reduction limit), Yg (no-load opening), and Yk (pressure regulator opening).
(3) Calculation methods involve determining valve opening time, slow closing time, flow reduction limits, and checking pressure drop conditions.
**4. Setting Parameters for Pressure Regulating Valves**
Before commissioning, all equipment must be installed and adjusted according to calculated parameters. Initial adjustments include simulating actions to remove air, setting slow closing times, and calibrating throttles for two-stage closure.
**5. Conclusion**
The TFW-type pressure regulating valve offers numerous advantages, including safety, reliability, and ease of maintenance. Since the 1980s, hundreds of Chinese hydropower stations have replaced surge tanks with these valves, with no safety incidents reported. Even in developed countries, pressure regulators are widely used. Future improvements, such as adding stroke signal devices, will enhance their performance in modern systems.
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