Pressure control valve, impact

Minor—any event that may cause minor injury or minor system damage, but does not significantly impact the mission (e.g., pressure control valve fails open, causing pressure drops and increased caustic levels)... 

Control-valve configuration impacts the resistance to flow through the valve. The amount of resistance, or pressure drop, will vary greatly, depending on type, size, and position of the valve s flowPressure-drop formulas can be obtained for all common valve types from several sources (e.g.. Crane, Technical Paper No. 410). 

The Naturalis from Lapua is a 99 percent copper hunting bullet. It includes a novel, proprietary pressure-regulating valve that controls bullet expansion. This combination results in a bullet that expands symmetrically into the shape of a mushroom immediately upon impact. It works perfectly within terminal velocities of 500 m/s to 1000 m/s [1640 to 3280 fps] and retains 100 percent of its weight. This results in a more powerful shock effect, cleaner wounds and more latitude in terms of shot angle, distance to target and hit accuracy. ... 

This upset initiates a runaway reaction that can catastrophically rupture the reactor. The impact of this event was judged to be extensive, which, as discussed in Table 6 Note 1, leads to a tolerable frequency of 10 /year for a single scenario. Several failures in the control system could cause this upset, with operating experience indicating that this type of upset occurs about once every 10 years. Protection per Table 5 was the Shortstop addition, but the runaway reaction may be too fast for the operator to respond to an alarm. This protection layer is not included for risk reduction. The area is normally occupied, so it was assumed that personnel could be impacted by the event. The pressure safety valves (PSVs) are only estimated to be 90% effective, since plugging is a common problem in this service. Since the PSVs share a common relief line, they are conservatively considered to be a single Independent Protection Layer. This led to an intermediate event likelihood of a 10 per year. Per the conservative assumptions used in this example, only the PSVs qualified as an IPL. The PHA team reviewed all the process safety risk issues and decided that a SIF was appropriate. As shown in Table 7, this requires a SIL 3 SIF. 

Task (4) The ISS is assembled as a single, inseparable container, requiring only one manual service valve, one solenoid, and one thermally activated pressure relief device, all incorporated into a gas control module (see Figure 4). The added cost and complexity of redundant components when using multiple, separable CH2 tanks is avoided by this approach. The gas control system is safeguarded from physical damage with impact absorbing foam... 

A significant issue to address is the impact of "fail safe" versus "non fail safe" actuators. Some designs such as diaphragm and piston actuators with hydraulic and pneumatic power are readily available as spring return valves. The failure or release of control pressure permits the spring to drive the actuator to its safe position. 

The major components of the mass spectrometer are a gas-handling manifold that enables the gas to be transferred from the ovens to the ion source, the ion source that consists of an electron impact source, magnetic mass analyzer with gap field of 6500 G, four different EM detectors, and an ion pump to ensure low pressure for the EMs. The gas handling system also included a controlled leak valve that could obtain Martian gas and feed the gas directly into the mass spectrometer for analysis. All the tubes in the gas handling system were heated to 35 C to ensure that there is no condensation of water and other volatile vapors on the hardware. 

Figure 4.8 shows the structure of a bow-tie diagram, which consists of an event tree that creates a top event, the safeguards and controls for which are analyzed with a fault tree. At the left of the diagram is the hazard, say a vessel containing hydrocarbons stored under pressure. Threats are events such as corrosion, external impact, and operating error, which could create an undesired event, in this case a release of hydrocarbons from the vessel. Between the threats and the undesired outcome are barriers such as operator training, relief valves and instrumentation. 

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