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Hydraulic Power Distribution
Published in Qin Zhang, Basics of Hydraulic Systems, 2019
Similar to relief valves, the pressure control performance of direct-acting pressure- reducing valves is also affected by the high differential between the cracking pressure and the target pressure attributing to the stiffness of the spring. The piloted-operated approach offers similar advantages to achieve better control performance over the direct-acting valves for the spool being balanced hydraulically by downstream pressure at both ends (Figure 3.16). A small pilot relief valve, usually built into the main valve body, releases the fluid in the main spring chamber to the tank when its pressure (the same as the downstream pressure) reaches the pilot valve spring setting. This fluid drain will cause a pressure drop across the spool due to orifice effect and will form a pressure differential to shift the spool toward its closed position against the light main spring force. To avoid a significant amount of energy loss from the pilot operation, the pilot valve releases only enough fluid to position the main valve spool to control the flow through the main valve to accomplish the pressure-reducing function. When the downstream pressure is high enough during a portion of the operation cycle, the main valve will be fully closed to stop flow supply to the circuit, and any internal leakage from the high-pressure end to the main spring chamber will be returned to the reservoir through the pilot-operated relief valve.
7 Fault trees
Published in K. C. Hignett, Practical safety and reliability assessment, 2002
This technique can be conveniently illustrated by reference to Figure 7.7 which refers to a protective system fault tree expressed in simplified overall terms. In reality the primary failure events A-G would each represent the end event of a sub-fault tree which would later be assembled into the overall composite fault tree shown. The failure event A representing primary mechanical failures attributed to shutdown valve 1 will in fact be constituted by a number of mechanical failures in the process valve itself such as gland stiction, spring failure, valve seat failures etc. The associated three-way electrical pilot valve will also contribute mechanical failures such as stiction, vent port blockage, leakage across valve seats etc. Hence the event A will have an associated Boolean reduced expression which may conveniently be assembled with those of the other end events B-G.
ORNL Progress in Disruption Mitigation Technology in Support of ITER
Published in Fusion Science and Technology, 2023
L. R. Baylor, T. E. Gebhart, S. J. Meitner, D. A. Rasmussen, C. Barbier, S. K. Combs, N. Commaux, P. W. Fisher, M. J. Gouge, T. C. Jernigan
In addition to the single pellet propellant valve used to deliver the gas, an array of six of these valves was fabricated[15] to enhance the flow rate further. The performance of the multivalve array was not significantly improved over the single-valve operation. Subsequently, a fast-opening, high-throughput two-stage gas valve that was developed for other applications was employed for MGI experiments on DIII-D. This valve was a pilot type with two stages of active components, shown in Fig. 5.[16] The pilot or first-stage section was magnetically driven by a solenoid coil and equipped with a 4-mm-diameter orifice. The pilot valve was energized to initiate opening the second stage and dumped gas from the upstream section of the second stage to the main valve outlet, and the resultant pressure differential across the large ~22.3-mm-diameter output orifice seat caused mechanical activation of the second stage. Both stages were equipped with hard polyimide stem tips and springs for sealing. This valve operated at pressures up to 35 bar and achieved a maximum flow rate of 106 Pa m3/s, or over 20 times the flow of the original single-propellant valve. This valve suffered from a slow opening of the second stage that allowed for a small quantity flow of gas to arrive before the peak flow, which was deleterious to achieve prompt plasma shutdown.
Post-industrial energy audit decision-making process: an Argentine case study
Published in International Journal of Sustainable Energy, 2022
Joaquín Alencastre Cordi, Daniel Alejandro Rossit, Miguel Ajís
Rolling valves are simply pressure reducing/regulating valves that are installed in the steam system of Figure 1. The rolling valve works by balancing the outlet pressure with the control spring. This moves a small shutter against a seat (the pilot). The fluid through the seat reaches directly to the diaphragm of the main valve, acting on it. Under stable conditions, the pressure below the pilot diaphragm balances the force attached to the adjusting spring. This seats the pilot valve and allows a constant fluid flow at a stable pressure through the main diaphragm. When the low pressure (i.e. valve outlet pressure) increases, the pilot valve closes, and the pressure is released from the diaphragm of the main valve through the control port, thereby closing the main valve and decreasing the water supply down. Any variation in flow or pressure will be immediately captured by the pilot diaphragm, which will act to adjust the position of the main valve, ensuring a constant low pressure.
Nonlinear PID actuator speed control in inverter based electro-hydraulic systems subjected to external leakage
Published in Australian Journal of Mechanical Engineering, 2020
M. A. Pascal, A Abou Elazm Aly, R Taher
Dasgupta (2005) analysed the dynamic characteristics of a proportional solenoid-controlled piloted relief valve through bond graph method. The model takes into account the flow forces, main and pilot valve dynamics, chamber fluid compressibility and nonlinear orifice flow. The results include the system’s response with respect to the step changes in command voltage applied to the solenoid. The effects of pre-compression of the pilot spring, the characteristics of the damping orifice on the performance of the system, as well as the effect of change of voltage signal on the valve’s performance have also been studied. The model relating to the various physical parameters to performance could be used to predict and improve the performance in the physical design of the valve. The model prediction was compared favourably with experimental data.