Vents sucking

Cooling of vapour in a vented vessel may cause sucking-back of process materials or ingress of air. 

If the vent line forms part of a blowdown system, it will have to be blanked to prevent air being sucked in. Make sure the blank is put on the flare side of the disconnection, not on the tank side (Figure 1-4). Note that if the tank is to be entered, the joint nearest the tank should be broken. 

When zinc was added to a tank, the extract fans were operated at full rate with the vent closed. No air could be sucked in, and the concentration of hydrogen rose rapidly above the upper flammable limit (75%). 

When the rate of production of hydrogen fell, the fans were again switched to full rate, this time with the vent open. Air was sucked in, and the concentration of hydrogen fell rapidly below the lower flammable limit. 

To prevent leaks of carbon monoxide and hydrogen from the glands of a number of compressors getting into the atmosphere of the compressor house, they were sucked away by a fan and discharged through a small vent stack. Air leaked into the duct because there was a poor seal between the duct and the compressor. The mixture of air and gas was ignited by lightning. 

In the vent pipes of storage tanks containing a flammable mixture of vapor and air (Section 5.4.1). Such flame traps should be inspected regularly and cleaned if necessary. Section 5.3 a described how a tank was sucked in because the flame arrestors on all three vents had not been cleaned for two years. 

LLO to washed solvent drum will flash and be sucked into vent system. 

Work in the Hood. A hood is a specially constructed workplace that has, at the least, a powered vent to suck noxious fumes outside. There s also a safety glass or plastic panel you can slide down as protection from exploding apparatus (Fig. 1). If it is at all possible, treat every chemical (even solids) as if toxic or bad smelling fumes came from it, and carry out as many of the operations in the organic lab as you can inside a hood, unless told otherwise. 

This suggests that the pressure in a water drain can get so low, that air could be sucked out of the bathroom and down the drain. Of course, we all see this happen several times a day—typically when we flush a toilet. So much air is drawn into the water drainage piping, that we install vents on our roofs, to release this air. The only requirement, then, for vapors to be drawn into a flowing nozzle is for the nozzle exit loss to be larger than the static head of liquid above the nozzle. 

For a surface condenser to work properly, noncondensable vapors must be sucked out of llie shell side. This is done with a two-stage jet system, as shown in Fig. 18.3. When I was first commissioned the jets, they were unable to pull a good vacuum. Moreover, water periodically blew out of the atmospheric vent. I found, after considerable investigation, that the condensate drain line from the final condenser was plugged. 

The mercury valve consists of a tube dipping about 0.5 in. into some mercury in a vented test tube. This allows the reaction to be carried out under a slight pressure of chlorine. The checkers found a water valve to be more satisfactory. The outlet tube was made to dip about 7 in. into water in a vented glass tube. A trap (125-ml. suction flask) was placed between the water valve and the reaction flask to prevent water from being sucked into the reaction mixture. 

The mercury bubbler C acts as a safety vent and controls the pressure in the apparatus. A ball valve near the top of the inlet tube prevents the mercury being sucked into flask B in the event of the automatic control valve D becoming blocked. 

It was also observed that the number of discharge residue particles on the firing hand decreased markedly as the bullet velocity increased. One possible explanation for this is that the greatly increased suction in the wake of the faster bullet causes more particles to be sucked out of the muzzle leaving fewer to exit from other vents and to be deposited on the hand. This... 

In another tank collapse incident, a tank containing a solution of ammonia and water was being emptied and cleaned. After employees emptied the tank of liquid ammonia, they added water to rinse the vessel. While the water was being added the sides of the tank were sucked in. The ammonia vapor remaining in the tank dissolved in the water so rapidly that air could not enter through the vent to prevent the collapse. [8]... 

He merely placed a small opaque PVC plate over the opening to stop sunlight from entering the scrubber. By doing so he unknowingly modified the vent. The loose-fitting PVC plate restricted air flow into the tanks (and almost totally blocked the flow) as acid was periodically pumped out at 50 GPM (11.4 m3/hr). The internal tank pressure dropped and the top of one tank sucked in due to a partial vacuum. 

After shutting off the roughing and fore pumps, open Stopcocks 5 and 6 to vent the pumps (this action prevents the mechanical pump oil from accidentally being sucked into the vacuum line). 

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