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Hydraulic Power Distribution
Published in Qin Zhang, Basics of Hydraulic Systems, 2019
A pilot-operated relief valve usually has much less pressure override than a direct-acting counterpart because the former uses a much softer spring than the latter. This feature allows a pilot-operated relief valve to be set at a much higher cracking pressure than a direct-acting one for the same full-flow pressure. It is not uncommon for a pilot-operated relief valve to be set at a cracking pressure at 90% of the full-flow pressure, while a direct-acting valve is normally set at a much lower level (Figure 3.13). This higher cracking pressure can effectively improve system efficiency because less pressurized fluid is discharged during the releasing process. While a pilot-operated relief valve can maintain a system operating at a more constant pressure, its response is generally slower than that of a direct-acting counterpart, mainly because of the two-stage procedure in pressure release. In addition, the cost is much higher to manufacture pilot-operated relief valves than direct-acting ones because of their complexity in structure.
Hydraulic Systems
Published in Anton H. Hehn, Fluid Power Troubleshooting, 1995
As system pressure rises, the pressure in the passage rises as well and when it reaches the setting of the pilot valve, the pilot valve opens. Oil is released behind the main spool or control chamber in which the main spool bias spring is located faster than it can enter through the orifice through the skirt of the main spool and the main spool is no longer balanced. The oil passing through the pilot valve is directed back to tank. Thus the unbalanced condition of the main spool permits excess fluid passage back to tank at a rate sufficient to maintain the desired set pressure. The pilot valve acts as a master adjustment and the piloted main relief valve poppet spool follows in a mirror image pattern to that of the pilot to provide the desired pressure value. The valve closes again when inlet oil pressure drops below the setting of the pilot valve. Pilot operated relief valves have less pressure override than do direct-acting relief valves.
Pressure Control
Published in John S. Cundiff, Michael F. Kocher, Fluid Power Circuits and Controls, 2019
John S. Cundiff, Michael F. Kocher
A pilot-operated relief valve has the same function as a direct-acting relief valve; however, it is typically used for “pressure regulation” vs. “over-pressure control”. It has a different pressure vs. flow curve as shown in Figure 3.8. (Remember, these curves are idealized. For the comparison, we assume that both valves have the same cracking pressure.) The pilot-operated valve opens completely over a narrow pressure range. This allows the circuit to operate over a wider pressure range without loss of fluid over the relief valve.
Availability of the Emergency Safety Electrical System of a Konvoi Nuclear Power Plant Considering Mobile Arrangements of Diesel Generators After Fukushima
Published in Nuclear Technology, 2023
D. P. Dionizio, P. L. C. Saldanha, P. F. Frutuoso E Melo, C. M. F. Lapa
Zubair et al.[14] simulated an SBO accident using a KEYMASTERTM generic pressurized water reactor (GPWR) simulator. The accident scenario consists of two stages. The first is concerned with observing GPWR behavior under a pure SBO situation whereas the second one aims to compare the first-stage SBO accident with additional failure of the stuck-open pilot operated relief valve like the one that took place at Three Mile Island. A comparison of the two stages was made, analyzing hot and cold leg temperatures, steam generator (SG) pressure, SG water level percentage, pressurizer pressure, fuel temperature, and containment pressure. The simulation results suggest that failure to close the valve in question has a negligible impact on the temperature of the hot and cold legs, resulting in lower overall pressure in the SG but higher pressure in the pressurizer. The nuclear fuel temperature exceeded the risk assessment threshold of 726.7°C for both scenarios. The survey results will help in the future to better understand accidents at Advanced Pressurized Water Reactors (APR-1400).
Detecting Anomalies in Simulated Nuclear Data Using Autoencoders
Published in Nuclear Technology, 2023
Pedro Mena, R. A. Borrelli, Leslie Kerby
One final note is that the use of autoencoders should not be limited to just security applications. As the models are able to detect high levels of noise with autoencoders, these could also be used in the area of detecting failures with equipment. Nuclear power plants rely on a number of sensors and instruments to provide operators at the facility information needed to properly run the facility. The use of an autoencoder to detect malfunctions and failures with these types of sensors would be an approach worth exploring. For example, if a sensor was to fail, the autoencoder should detect the noise from the data being transmitted to the operator. This could potentially allow for quicker identifications of equipment failures, such as the pilot-operated relief valve (PORV) failure at Three Mile Island. This would add another layer of protection to nuclear power and contribute to the safety efforts at power plants.
Risk-Informed Safety Analysis for Accident Tolerant Fuels
Published in Nuclear Science and Engineering, 2020
Carlo Parisi, Zhegang Ma, Diego Mandelli, Nolan Anderson, Hongbin Zhang
The following events are described for each ET branch or SBO scenario of Table I: turbine-driven auxiliary feedwater (TDAFW) availability: yes or nopressurizer (PZR) pilot-operated relief valve (PORV): closed or stuck openrapid secondary-side depressurization (RSD): effectuated by the operator using the steam generator (SG) PORVs. The considered ratio of depressurization is ~55 K/h [100°F/h (Ref. 62)].reactor coolant pump (RCP) seal LOCA: a variable leakage rate [no leakage, 21, 76, 182, 300, and 480 gallons per minute (gpm)] from each of the RCP is assumed.alternating-current (AC) power recovery timeemergency recovery actions after success or failure of AC recovery and loss of direct-current (DC) power: manual control of the auxiliary feedwater (AFW-MAN), manual SG depressurization, late off-site power recovery (OPR), high-pressure injection (HPI), high-pressure injection - recirculation mode (HPR), low-pressure injection - recirculation mode (LPR).