Pressure-driven leaks

Estimates of diffusive leakage using the same geometry used for pressure-driven leakage, and the diffusivity values in Table 5.1 show leak rates of 0.04 sccm/cm2 for pure hydrogen, or 0.008 sccm/cm2 for reformate or nitrogen diluted hydrogen streams. Thus, diffusive leak rates of 2 to 10 times that of hydrodynamic may be expected. 

Membrane installations operated in nuclear industry are pressure-driven systems majority of them are reverse osmosis plants. Uncontrolled growth of operation pressure may result in module damage and valves leaks resulted in contamination hazard. The selection of appropriate pumps and security devices can avoid the danger of pressure overgrowth and its detrimental implications. The security valves outlets have to be connected with existing waste distribution systems to direct the eventual leaks to the waste collecting tanks. 

The solution to be electrosprayed is passed through the electrospray capillary (ESC) by means of a motor driven syringe. Some of the spray containing the ions then enters the pressure reducing capillary (PRC) leading to the forechamber (FCH) of the ion source. The exit tip of the PRC directs the gas jet in a direction parallel to the bottom of the FCH, i.e. across the interface plate (IN). An orifice of 4 mm diameter in the interface plate connects the FCH to the reaction chamber (RCH). The ions in the jet exiting from the PRC are deflected out of the jet towards this orifice and into the RCH by means of an electric field applied across the FCH. A weak field is also applied across the RCH. At the bottom of the RCH a small orifice, 100 pm diameter, allowed some gas and ions to leak into the vacuum of the mass... 

In addition to the vacuum valves, which perform solely an isolation function (fully open - fully closed position), special valves are needed for special functions. Typical are variable leak valves, which cover the leakage range from 10" ° cm /s (NTP) up to 1.6 10 cm /s (NTP). These valves are usually motor driven and suitable for remote control and when they are connected to a pressure gauge, the process pressures can be set and maintained. Other special valves fulfill safety functions, such as rapid, automatic cut-off of diffusion pumps or vacuum systems in the event of a power failure. For example, SECUVAC valves belong to this group. In the event of a power failure, they cut off the vacuum system from the pumping system and vent the forevacuum system. The vacuum system is enabled only after a certain minimum pressure (about 200 mbar) has been attained once the power has been restored. 

A systematic view of the relevant elements is depicted in Figure 17.10. The deposited clusters can be exposed to different reactant gases by two kinds of valves. First, they can be exposed isotropically to e.g. O2 by a commercial, ultra-high vacuum (UHV) compatible, variable leak valve. Second, reactant molecules (e.g. CO) can be introduced via a pulsed molecular beam produced by a piezo-electric driven, pulsed valve. This pulsed valve has a high pulse-to-pulse stability (time profile), and allows the study of catalytic processes on supported clusters at relatively high pressures (up to 10 mbar). Furthermore, a stainless steel tube is attached to the pulsed nozzle in order to collimate the molecular beam and to expose the reactant molecules to the substrate only. The pulse duration at the position of the sample can, in principle, be varied from 1 ms up to continuous operation. For the experiments described below a constant pulse duration of about 100 ms was used. The repetition rate of the pulsed valve can be up to 100 Hz. The experiments were carried out at 0.1 Hz the 10 s interlude allows the reactant gas to be pumped completely. 

Oil, used for lubricating the gears and bearings, is separated from the compressed airstream by labyrinth seals. Shown in Figure 3.31, the seals consist of two separate components, an air seal and an oil seal. In between the two, the seal is open to atmosphere. Any oil bypassing the oil seal leaks to atmosphere. The air seal is always at a higher pressure so that any leaks are always from air to atmosphere and oil cannot enter the process fluid. Oil is typically provided by a shaft-driven pump with a standby motor-driven pump available. 

Up to now the safety evaluation of a secondary sodium leak accident has been based on the severest temperature-driven pressure rise, assuming the largest scale of sodium leak. This was chosen since the loss of integrity of the building due to the pressure rise in the room has a critical effect on loop separation and therefore accident limitation. 

The sodium in the primary vessel flows upward from the core and flows downward in the tube side of the IHX to reach the cold plenum. The sodium in the cold plenum is driven into the core by the primary EM pump. On the other hand, the secondary sodium pressurized by the secondary EM pump enters the IHX through the secondary cold leg piping. The sodium flows upward in the IHX shell ride and enters the SG through the secondary hot leg piping. After heat transfer to water/steam, the sodium flows to the secondary EM pump. To keep the secondary vessel in an isothermal condition, a nall amount of coolant leaks into the secondary vessel from the upper part of the EM pump. 

One or more small multi-stage high-pressure compressors which are directly driven by motors of about 5 to 25 H.P., are used to pressurize the accumulator. The initial filling occupies a few days, whereupon the compressor will have to be used from time to time only to replenish air when losses due to small leaks or to absorption have occurred. 

Air brakes on railway trains, where the brakes are held in the off position by massive air pressure created in the brake system. Should a brake line split, or a carriage become de-coupled, the air pressure will be lost and the brakes applied. It is impossible for the train to be driven with a leak in the brake system... 

A leak in the pressure vessel of the seismometer would allow air to pump in or out driven by atmospheric pressure changes, and this would cause the proof masses to rise or fall buoyed by changing air density inside the vessel. This creates a very pronounced noise that is strongly vertical. Pressure leaks mostly arise in seismometers that provide service access ports such as for manual mass centering that may not have been properly closed or where the seals have deteriorated. 

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