Positive pressure methode

The specimens should wherever possible be examined in a configuration corresponding to their later application - components for vacuum applications using the vacuum method and using the positive pressure method for parts which will be pressurized on the inside. 

When using the positive pressure method it is sometimes either impractical or in fact impossible to measure the leakage rate directly while it could certainly be sensed in an envelope which encloses the test specimen. The measurement can be made by connecting that envelope to the leak detector or by accumulation (increasing the concentration) of the test gas inside the envelope. The bombing test is a special version of the accumulation test (see Section 5.7.4). In the so-called sniffer technique, another variation of the of the positive pressure technique, the (test) gas... 

Forced-Recirculation Reboilers In forced-recirculation reboilers, a pump is used to ensure circiilation of the liquid past the heattransfer surface. Force-recirculation reboilers may be designed so that boiling occurs inside vertical tubes, inside horizontal tubes, or on the shell side. For forced boihng inside vertical tubes. Fair s method (loc. cit.) may be employed, making only the minor modification that the recirculation rate is fixed and does not need to be balanced against the pressure available in the downcomer. Excess pressure required to circiilate the two-phase fluid through the tubes and back into the column is supphed by the pump, which must develop a positive pressure increase in the hquid. 

Both the dry sump and wet sump method of oil misting have a slight positive pressure in the bearing housing. This prevents contaminants and even humid air from entering the bearing ehamber. 

There was no significant damage to equipment in the fire tests, and it was demonstrated that a Jet Airmix mixer may safely handle the mixing of RP formulations on a routine basis. Since a high risk of fire is always associated with any method of transfer of RP, a pneumatic conveying system [dynamic air, two phase positive pressure transfer system was evaluated to load RP into the Jet Airmix mixer. Electrostatic charge measurements were minimal and indicated the system was satisfactory to load the blender. 

Today leak tests for vacuum systems are usually carried out with helium leak detectors and the vacuum method (see Section 5.7.1). The apparatus is evacuated and a test gas is sprayed around the outside. In this case it must be possible to detect (on the basis of samplings inside the apparatus) the test gas which has passed through leaks and into the apparatus. Another option is to use the positive-pressure leak test. A test gas (helium) is used to fill the apparatus being inspected and to build up a slight positive pressure the test gas will pass to the outside through the leaks and will be detected outside the device. The leaks are located with leak sprays (or soap suds, 5.4.5) or - when using He or H2 as the test gas - with a leak detector and sniffer unit (5.7.2). 

By reversing the position of liquid and gas assumed in the preceding section we obtain the bubble pressure method. The theory corresponds closely with that of the drop weight and has been developed by Cantor, Feustel and Schrodinger (Ann. d. Physih, xlvi. 413,1915). 

Two independent means, graphical relative pressure methods, are used to obtn EW EV from peak pressure measurements. Two comparable methods obtn these figures of merit from positive impulse data. There is also described a method for detg EW Si EV from an analytical study of positive impulse data... 

Positive pressure/submersion V acuum/ submersion Dye penetration Vapor/particle leak testing Visual inspection methods Light transmission tests... 

ASTM E 2010 Standard Test Method for Positive Pressure Fire Tests of Window Assemblies (withdrawn)... 

This chapter covers examples of system modifications made to prepare for maintenance. Each unwise modification created equipment damage. These incidents were simple changes intended to isolate, protect, clean, or clear equipment, and the methods chosen created problems. In some cases equipment was subjected to partial vacuum or positive pressure beyond the tolerable design limits. 

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