Leaking valves

TROUBLE EXCESSIVE CARBON ON VALVES PROBABLE CAUSE(S) 1. Excessive lube oil. 2. Improper lube oil (too light, high carbon residue). 3. Oil carryover from inlet system or previous stage. 4. Broken or leaking valves causing high temperature. 5. Excessive temperature due to high pressure ratio across cylinders. 

The nitrogen supply used to purge the metal cabinet was also used to blow out the dryers. When the iiiirngcn supply pressure fell occasionally, solvent from the dryers entered ihrtmgh leaking valves into the nitrogen supply line,, ind into the metal cabinet. Low nitrogen pressure allowed air diffusion into the cabinet. 

A mechanic was affected by fumes while working on a steam drum. One of the steam lines from the drum was used for stripping a process column operating at a gauge pressure of 30 psi (2 bar). A valve on the line to the column was closed, but the line was not slip-plated. When the steam pressure was blown off, vapors from the column came back through the leaking valve into the steam lines (Figure 1-3). 

No matter how well installed, insulation is always at risk of contamination from outside sources. Overfilling of vessels, leaking valves and flanges, oil thrown off from rotating transmission shafts and motors can all penetrate protective cladding or lining systems. Consideration of any insulation s compatibility with possible contaminants should be considered in these situations. 

During the last year we have built an FTMS instrument specifically designed for laser-induced thermal desorption from single-crystal surfaces. Figure 5 is a perspective drawing of the Instrument. The chamber is pumped by a 150 1/s ion pump and has a base pressure of 2.0 X 10- torr. Gases are Introduced through sapphire-sealed leak valves from a diffusion pumped gas manifold. 

Methyl radicals were produced by pyrolysis of azomethane (CH3N2CH3). Azomethane was synthesized as describe earlier [18]. It was purified periodically by fteeze-pump cycles at 77 K, and the gas purity verified by RGA. The methyl radical source was similar to that developed by Stair and coworkers. [10, 11] The source was made of a quartz tube with 3 mm OD and 1 mm ID, resistive heating was supplied by means of a 0.25 mm diameter tantalum wire wrapped outside the quartz tube. The len of the heating zone was 4 cm, recessed from the end of the tube by 1 cm. An alumina tube around the outside of the heating zone served as a radiation shield. Azomethane was admitted to the hot tube at a pressure of 1x10-8 to 1x10-7 Torr via a high-vacuum precision leak valve. The pyrolysis tube was maintained at about 1200 K, adequate to decrease the major peaks in the mass sp trum of the parent azomethane at 58 and 43 amu by at least a factor of 100. 

It should be noted that these can also be caused by other problems besides tank leakage, such as leaking valves, loose fittings, or other factors. 

Whenever possible, we perform experiments in the same part of the surface before and after some operation. The operation may involve exposure of the surface to a reactant such as water or 02, for example or it may be some switch in the functionality of the microscope, for instance, imaging first in AFM mode and then in STM mode. For reactions, we simply stop the scan and retract the tip by up to 1000 nm, which ensures it does not crash when we admit gases or vapors to the chamber via the high-precision leak valves. 

A leaking valve allowed butadiene to accumulate in a pipeline exposed to an inerting gas containing up to 2% of oxygen. Peroxide formed and initiated popcorn polymerisation which burst the pipeline. 

Fault trees also assume that failures are hard, that a particular item of hardware does not fail partially. A leaking valve is a good example of a partial failure. Also, the approach assumes that a failure of one component does not stress the other components, resulting in a change in the component failure probabilities. 

Pascagoula, MS, USA, Chemical Plant, Explosion/Fire Suspected leaking valves released vapors that were ignited 10,000,000 loss... 

Fig. 3. Schematic drawing of the high pressure electron spectrometer. A, Argon ion gun D, differentially pumped region EL, electron lens G, gas cell HSEA, hemispherical electron analyzer LO, two-grid LEED optics LV, leak valve M, long travel rotatable manipulator P, pirani gauge S, sample TSP titanium sublimation pump W, window X, twin anode x-ray source.

Figure 6. Diagram of our 1-atm ion mobility spectrometer (IMS) apparatus (a) stainless steel source gas dilution volume, (b) septum inlet, (c) needle valve, (d) Nj source gas supply, (e) source and drift gas exhaust, (f) flow meter, (g) pressure transducer, (h) insulated box, (i) drift tube, (j) ion source, (k) Bradbury-Nielson gate, (I) Faraday plate/MS aperture, (m) drift gas inlet, (n) universal joint, (o) electrostatic lens element, (p) quadrupole mass filter, (q) 6"-diffusion pump, (r) first vacuum envelope, (s) channeltron electron multiplier, (t) second vacuum envelope, (u) 3"-dif-fusion pump, (v) Nj drift gas, (w) leak valve, (x) on/off valves, (y) fused silica capillary, (z) 4-liter stainless steel dilution volume, (aa) Nj gas supply.

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. 

Variable-leak valve Inlet valve Gas supply Throttle valve Vacuum pump... 

The atomically clean, well-ordered Ni(lOO) surface was obtained by using a standard cleaning procedure as described in detail elsewhere [17]. The deposition of potassium was achieved by evaporation from a SAES getter source [18]. Reagent grade (99.999% purity) gases of O2, H2 and CH4 were introduced into the UHV chambers through leak-valves. 

The following discussion provides a plant caculation method for lower explosion limit concentrations for flare stacks or leaking valves that could ignite. 

The nitrided catalyst (0.2 g) was heated in situ to 373 K in flowing He and held at RT for 1 h after the preparation. The catalyst was then heated at 0.0167 Ks-1 to 1263 K at a flow of 11.1 pmols-1 H2 (or He) for the TPR (or TPD) studies. The gases desorbed from the sample were monitored on-line using an ULVAC MSQ-150A quadrupole mass spectrometer equipped with a variable-leak valve heated by heating tape. 

D20 vapor was admitted into the chamber through a variable leak valve. Photogenerated projects were detected with a UTI quadru-pole mass spectrometer. The system was sensitive to H2 generation rates as low a 0.3 monolayers/hour and had still higher sensitivity to oxygen. 

The same technique can be used in pumping stations for the fast determination of the point of leak (valves, joints, connections, etc.). In this case it is based on the temperature difference of the metallic part involved in the leak. By analysing the images of the structures and equipment it is usually not difficult to determine the parts that are responsible for the leak. 

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