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Adjustment and troubleshooting of security system failures 1. Abnormal operation of the quick-shut valve 1.1 Failure of the quick-shut valve to open properly due to improper operation: In turbines where the quick-shut valve is opened using a starting regulator, it is necessary to switch between starting oil and quick-shut oil during the opening process. However, when the regulator knob is turned rapidly and continuously, the pressure increase of the quick-shut oil in the cylinder is slower than the pressure decrease of the starting oil, resulting in the piston disc separating from the piston and thus preventing the quick-shut valve from opening. The proper procedure is to pay attention to the pressure gauge while operating the handwheel; when the quick-shut oil pressure is established and the starting oil pressure begins to drop, the operation should be carried out as slowly as possible or paused for a few seconds before continuing, so that the quick-shut valve can open properly. 1.2 Failure of the quick-shut valve to open due to internal leakage in the cylinder: An excessive radial gap between the cylinder and the piston results in significant leakage of the actuation oil, leading to a drop in pressure. This lack of pressure prevents the piston from being pushed against the piston disk; without the piston in contact with the piston disk, it is not possible to generate pressure for the quick-shut function, and as a result, the quick-shut valve cannot open. This type of fault can only be resolved through maintenance, such as installing seals between the cylinder and the piston or using a single piston. 1.3 Abnormal operation of the quick-close valve caused by scaling on the valve stem, bending of the valve stem, etc.: Regularly conduct tests on the operation of the quick-close valve (see 1-2300- and 3-1400-). If an increase in test oil pressure is observed, it is likely that there is scaling on the valve stem, scaling in the cylinder, or bending of the valve stem; repairs should be carried out promptly to identify the cause and eliminate it. To prevent the valve stem from bending, spare valve stems should not be placed horizontally but should be stored hanging. 2. Oil leakage from the quick-shut valve cylinder (external leakage). 2.1 The sealing ring is not installed properly, resulting in a failure to provide sealing. The corrective action is to reassemble the seal and compress the sealing ring; if the specification of the sealing ring is incorrect, it must be replaced. 2.2 During assembly, if the valve stem and the seal sleeve are not aligned, or if the valve stem bends and comes into contact with the sleeve, this can cause the valve stem to become abraded, damaging the seal ring and resulting in oil leakage from the cylinder. Remedial actions: Repair or replace the valve stem and sleeve, replace the seal ring, and reassemble it carefully. 3. Fault of the incorrect throttle slide valve: The incorrect throttle slide valve is composed of a rotating disc and a slide valve body that are bonded together (see 1-1910-). In some turbines, the rotating disc can separate from the slide valve body due to an increased rotational resistance torque or a decrease in the strength of the adhesive. In such cases, since the slide valve body no longer rotates, the response time of the control system increases significantly. When the set value of the regulator is changed, the secondary oil pressure changes, but the hydraulic actuator either does not respond or exhibits excessive movement. At the same time, oil leaks from the vent of the incorrect throttle valve, and there is no vibration felt when touching the inlet and outlet pipes of this valve. Remedial action: Shut down the machine promptly and replace the spare throttle spool valve. The removed spool valve can be re-adhered by itself. Before bonding, the cured adhesive layer on the bonding surface should be cleaned thoroughly using a scraper or sandpaper. A single-component anaerobic adhesive with a shear strength of >14.7 Mpa at room temperature can be used for bonding, and the bonding process should be carried out in accordance with the requirements of the adhesive used. 4. High-frequency oscillation of the secondary oil pressure: In turbines that use hydraulic amplifiers, under certain operating conditions, oscillations in the secondary oil pressure can cause the pointer of the secondary oil pressure gauge to shake, the secondary oil pipelines to vibrate, and rapid fluctuations in the unit’s load or speed to occur without any reduction in these fluctuations. In such cases, it is possible to reduce the rotation frequency of the slide valve and its amplitude by slightly reducing the flow rate through the check valve on the secondary oil pipeline, or by adjusting the throttle valve. If necessary, pipe clamps can be installed on the secondary oil pipeline to suppress the oscillations. 4.1 The turbine fails to start properly. When a turbine equipped with a hydraulic or mechanically-hydraulic governor is started, after the rapid acceleration phase, the control valve suddenly closes, preventing normal startup. This situation is usually caused by improper setting of the amplifier’s \"cut-off point\", as shown in 1-1830-. 4.2 Load (speed) fluctuations In turbines equipped with hydraulic or mechanically-operated speed regulators, fluctuations in load (speed) that occur either rapidly or slowly during operation can arise. There are many reasons for instability in the control system; here two of them are listed: 4.2.1 An excessive axial gap at the connection between the amplifier fork and the proportional lever allows the fork to move, which in turn disturbs the follower piston and causes secondary fluctuations in oil pressure, leading to fluctuations in load or speed. Remedial action: During maintenance, replace the gaskets and control the axial clearance at the connection to between 0.02 and 0.03 mm, so that the fork can rotate freely without any axial movement. 4.2.2 In turbines equipped with PG-PL governors, an inappropriate opening of the governor compensation needle valve in relation to the unit’s characteristics can lead to instability in the control system. The opening degree of the compensation needle valve can be adjusted while the unit is in operation. If the fluctuation speed is very slow, it indicates that the needle valve is open too little; in such cases, the valve should be turned counterclockwise to increase its opening degree. If the fluctuation period is short, the valve should be closed further. Whether the valve is opened or closed, adjustments should be made slowly while monitoring the operation of the unit, until the system stabilizes. After that, the set value of the governor can be changed; the system will respond immediately, and after a slight overshoot it will return to a stable state. In this case, it can be considered that the adjustment of the compensation needle valve is satisfactory. Once the valve has been properly adjusted, it is usually not necessary to make further adjustments. 4.3 Electro-hydraulic converter: In turbines equipped with electro-hydraulic control systems, after operating for a period of time, if the relationship between the current signal of the electro-hydraulic converter and the output oil pressure differs from the data obtained during the trial operation, a decrease in the oil pressure corresponding to the same current signal is likely due to poor cleanliness of the oil system or clogging of the inlet filter of the electro-hydraulic converter. Remedial measures: After a normal shutdown, clean the filter screen and reinstall it; then measure the relationship between current and oil pressure. If everything returns to normal, the system can be put back into operation. At the same time, it is necessary to strengthen the maintenance of the oil system to improve its cleanliness ； If the test results are abnormal, you can try to re-tune it by using corrected initial values and ranges. During operation, if a fault occurs in the electro-hydraulic converter due to reasons other than external factors, it is best to shut down the system, replace it with a spare electro-hydraulic converter, and contact the manufacturer of the converter to discuss the repair procedures. If one disassembles the electro-hydraulic converter for maintenance, various constraints often prevent achieving the desired results.