Vacuum vented

In general, vacuum vents and inert or gas repressuring systems are not considered an acceptable alternative to vacuum design for process equipment. Repressuring systems may be provided for process reasons, but they are not considered sufficiently reliable for equipment protection. Vacuum breakers are difficult to maintain tight and may admit air into the equipment. 

Use of Pressure-Vacuum Vent Valves for Atmospheric Pressure Tanks to Reduce Evaporadon Loss... 

Research has shown that pressure-vacuum vents are just as effective as flame arrestors for storage tanks against internal ignitions. 

Fig. 7 Extruder and extrusion. 1 Drive unit, 2 barrel inlet, 3 temperature control, 4 feed hopper and dosing unit, 5 vacuum vent, 6 barrel, 7 screw. (Reproduced with permission from Reifenhauser)...

Fire codes recommended installation procedures also detail specifics on pressure/vacuum venting devices and vent hne flame arresters. For example, codes mandate dilferent ventilation requirements for Class I-A liquids versus Class I-B or I-C liquids. Tank vent piping is generally not manifolded unless required for special purposes such as air pollution control or vapor recovery. As always, local codes must be consulted. 

Valve V3 is set to allow gas to exit the selected adsorber through the back pressure regular (BPR) as soon as the desired operating pressure is achieved. For depressurization, V3 is switched to allow the column exit gas to bypass the BPR and be vented through valve V4. V4 is a vacuum/vent selector and V5 allows a single pressure transducer to monitor system pressures at up to four selected points. 

A similar incident involving steam condensation was reported in the Hazard of Water in Refinery Process Systems [6], where the caption on a photo of a badly damaged tank states, A vacuum vent and one open hatchway was not enough to prevent damage when steam condensed and pulled in the top two courses of this 35 ft. diameter by 21 ft. high wash tank. ... 

The investigating team made several training and Management of Change recommendations and decided to eliminate the impulse valve (valve no. 4) connected to the pressure/vacuum vent. The elimination of the impulse valve removed the unintended... 

Features of tank trucks, top loading, pressurized top unloading, "spec plate and DOT classifications, pressure and vacuum vents, spill dam and rollover, and internal safety valve. 

B Formed sheet into female mold, a - Pressure box. b - Preheated, clamped sheet, c - Female mold with vacuum/vent holes. 

In order to produce a WPC product by the extrusion process, it is required to first melt the polymer, then mix the molten polymer with the dried wood fiber such that a homogeneous melt is achieved and any remaining moisture can be removed by vacuum venting. The extruder then compresses the homogeneous blend to pass through the die. Various extrusion configurations have been developed for WPC product manufacture [274], some of which are described below. 

Bulk solvent storage tanks should be equipped with pressure-vacuum vent devices that reduce vapor losses because of tank breathing" caused by temperature changes. 

Development of auxiliary equipment and technologies to improve the microinjection molding process, such as variotherm mold heating systems, vacuum venting, alignment techniques, etc. 

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