Vacuum failure

In addition to knowing the intended use for a vacuum line, you also need to know its history. By knowing the vacuum line s history, you can rule out the possible reasons for vacuum failure and proceed to locate the cause. For example, if yesterday a vacuum line was achieving a 10 6 torr vacuum, but today it can only achieve a 10 2 torr vacuum, something dramatic has obviously occurred, which is more likely to be a leak. On the other hand, if the same drop in vacuum occurred gradually over a period of several weeks, it is very unlikely the cause is a leak and is more likely caused by gradual component failure. 

Finally, ESl-MS is a rugged technique. Since ionization occurs at atmospheric pressure, there is no worry about vacuum failure. On a daily basis, the ionization chamber and the counter electrode can be easily checked and cleaned in a matter of minutes, while vacuum is maintained in the transport and mass analyzer regions. Pump oil changes are about as frequent as with GC-MS (about three to four months), far less than in thermospray and particle beam LC-MS. 

Nearly all beamlines, including those for XRF, XAS and XRD, contain a similar set of components. The X-rays from a BM or an ID are transported to the experimental station by a very sophisticated set of components designed to protect the ring from catastrophic vacuum failure, and the scientists from X-rays. 

Vacuum Failures Pressure reduction in a container can damage it. For example, a tank can collapse while being drained if there is nothing to replace the removed contents. Even if there is venting, the vent line must provide adequate flow rates to prevent formation of a vacuum. 

Answer by Author About 300 panels measuring 30X40 in. were constructed and tested for vacuum stability when used in refrigerator doors. Each panel was equipped with a Pirani-type vacuum gauge. The vacuum history of all these panels was followed for about four years and several of them for 10 years. To our knowledge, there were no instances of vacuum failure. 

The following containment system impairments are analysed in turn loss of air coolers, loss of dousing, open ventilation dampers, deflated airlock door seals and open airlock doors. In Canada, where four multi-unit stations have vacuum containment, a number of additional containment impairments are considered partial or total loss of vacuum failure of the instrumented containment pressure relief valves to open or close and failure of one bank of self-actuating containment pressure relief valves. These failure combinations will not, however, be discussed in detail in this report since no stations outside Canada have this type of containment. 

Fig. 10. Long-term effect of aging in vacuum on flexibiUty of Parylenes C, D, and N at elevated temperature. Failure = 50% loss in tensile strength.

Failure of vacuum Design vessel to accommodate maximum system control vacuum (full vacuum rating) resulting in possi-. , elief system bility of vessel collapse pressure alarm and interlock to inert gas supply Select/design vacuum source to limit vacuum capability ASME VIII CCPS G-23 CCPS G-39... 

Failure of compo- Ensure all system components, including flexible nents in connectors are rated for maximum feasible subatmospheric vacuum conditions pressure convey-, Ensure adequate pressure control system and ing operations. back-up (e.g., vacuum relief devices) API 2000 CCPS G-3 CCPS G-11 CCPS G-22 CCPS G-29 CCPS G-3 9... 

Overfill by plugging, blinding cloth, failure to start underflow pump, loss of vacuum or by operator error. 

The catalyst is previously prepared in an apparatus for catalytic hydrogenation, in which are placed 0.5 g. of palladous chloride, 3.0 g. of Norite, and 20 ml. of distilled water. The bottle is swept out with hydrogen and then shaken with hydrogen for 2-3 hours at 2-3 atmospheres (40 lb.) pressure. The palladium on carbon is collected on a Biichner funnel, washed with five 50-ml. portions of distilled water, then with five 50-ml. portions of 95% ethanol, and finally twice with ether. Upon drying, about 3 g. of the catalyst is obtained. It is stored in a vacuum desiccator over solid sodium hydroxide. If the reduction of the chloro-lepidine does not proceed normally, the used catalyst should be removed by suction filtration and a fresh 3-g. portion of catalyst added. Failure of the reduction step is usually due to an inactive catalyst or to impurities in the acetic acid or chlorolepidine. The palladium catalysts, prepared as described elsewhere in this volume, are presumably also satisfactory for the reduction of 2-chlorolepidine (p. 77). 

When you write on a blackboard with chalk, you are not unduly inconvenienced if 3 pieces in 10 break while you are using it but if 1 in 2 broke, you might seek an alternative supplier. So the failure probability, Pf, of 0.3 is acceptable (just barely). If the component were a ceramic cutting tool, a failure probability of 1 in 100 (Pf= 10 ) might be acceptable, because a tool is easily replaced. But if it were the window of a vacuum system, the failure of which can cause injury, one might aim for a Pf of lO and for a ceramic protective tile on the re-entry vehicle of a space shuttle, when one failure in any one of 10,000 tiles could be fatal, you might calculate that a Pf of 10 was needed. 

This, then, is our final design equation. It shows how the survival probability depends on both the stress (rand the volume V of the component. In using it, the first step is to fix on an acceptable failure probability, Pp 0.3 for chalk, 10 for the cutting tool, 10 for the vacuum-chamber window. The survival probability is then given by P = 1 -. ... 

The material properties of window glass are summarised in Table 18.1. To use these data to calculate a safe design load, we must assign an acceptable failure probability to the window, and decide on its design life. Failure could cause injury, so the window is a critical component we choose a failure probability of 10The vacuum system is designed for intermittent use and is seldom under vacuum for more than 1 hour, so the design life under load is 1000 hours. 

Incorrect specification of the disc. This includes overlooking intermittent vacuum conditions and other pressure/temperature transients, failure to predict corrosion, or operating at a pressure too close to the rupture disc pressure, resulting in fatigue failure. 

If designs are compared on the basis of count, then failure rates of each type of pint cither must be about the same, or be adjusted for the variations. For example, the parts count of vacuum-tube and solid-state television sets (using discrete components) are approximately the same, but their reliabilities are considerably different because of the better reliability of solid state components. 

Underpressure (vacuum) Withdrawals exceed inflow Thermal contraction Open outlet Pressure control system failure Low pressure... 

Electrical isolation Heat radiation Cooling coils Recent incidents Vacuum relief valves Accidents at sea Fires Problem sources Emulsion breaking Chimney effects Interlock failure Choosing materials. 

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