Gravity flow

Surface water can sometimes be obtained through gravity flow by locating aquaculture faciUties at elevations below those of adjacent springs, streams, lakes, or reservoirs. Coastal faciUties may be able to obtain water through tidal flow. 

Positive Pumps. Positive pumps employed by the food industry have a rotating cavity between two lobes, two gears that rotate in opposite directions, or a crescent or stationary cavity and a rotor. Rotary positive pumps operate at relatively low speed. Fluid enters the cavity by gravity flow or from a centrifugal pump. The positive pump also may use a reciprocating cavity, and may be a plunger or piston pump. These pumps are not truly positive with respect to displacement, but are used for metering product flow. 

Fig. 12. Gravity flow concentrators (a) Reichert cone (2), and (b) spiral, where (o) represent particles of low density and ( ), particles of high density (27).

When alloy piping or large bore piping is required, the associated equipment is located together as much as possible to keep the pipe mns short, preferably nozzle-to-nozzle by avoiding the piperack. Items such as elevated overhead condensers are located near the source and destination. Similarly, thermosyphon reboHers need to be placed adjacent to the column they reboH. Where gravity flow is required, these lines must be kept short and sloped. Space allocation for future additions must also be considered. 

Nutsche Filters A nutsche is one of the simplest batch filters. It is a tank with a false bottom, perforated or porous, which may either support a filter medium or act as the filter medium. The shiny is fed into the filter vessel, and separation occurs by gravity flow, gas pressure, vacuum, or a combination of these forces. The term nutsche comes from the German term for sucking, and vacuum is the common operating mode. 

Example 5 Solids Sampling by Linear Traversing Trajectory Cutter. Example 6 Slurry Sampling by Rotary Traverse of Gravity Flows. 

Operation of a traversing sampler for gravity flow of material for through-stream sampling is required to meet the following design factors ... 

Example 6 Slurry Sampling by Rotary Traverse of Gravity Flow Increment volume, quantity of slurry extracted hy one cutter rotation, is S from hulk slurry flow B expressed in voliime-per-imit time. R is cutter rotation per minute. D is cutter angle opening, with D/360 extraction ratio for continuous cutter rotation. 

Dyna Whirlpool A unique vessel design for capacities up to 100 t/h has been developed by the American Zinc Co. The separation occurs in a cyhndrical-shaped separatory vessel maintained in an in-chned position from horizontal. This system, known as the Dyna Whirlpool (DWT) process, provides for separate entiy of the medium and the feed sohds, as illustrated in Fig. 19-37. A distinct feature of this separator is that the feed enters the separator via gravity flow. Feed size may range from 0.05 to 0.0002 m (2 in to 65 mesh). Magnetite or ferrosilicon is generally used. 

Gravity Wheel Conveyors These can be used as pusher units set horizontally or inclined for gravity flow. They are highly standardized and are usually sold in 1.5- or 3-m (5- or 10-ft) sections special lengths are available at extra charge. Since wheel conveyors give what is essentially point suppoi t to containers, it is generally recommended that at least six wheels be located under the load at all times. 

An innovation is a direct-contact condenser mounted on the vapor body. A short piece of vertical pipe connects the vapor body with the condenser to minimize piping and pressure drop. This design also eliminates structural steel for support of a separate condenser. For cooling tower applications, the hotwell is elevated to permit gravity flow of water from the hotwell to the top of the cooling tower, thus eliminating the need for a pump. 

Solution flow by gravity to the point of discharge is desirable. When gravity flow is not possible, transfer components should be selected that require little or no dilution. When metering pumps or proportioning weir tanks are used, return of... 

Storage tanks for liquid caustic soda should be provided with an air vent for gravity flow. The storage capacity should be equal to 1.5 times the largest expected delivery, with an allowance for dilution water, if used, or two-weeks supply at the anticipated feed rate, whichever is greater. Tanks for storing 50 percent solution... 

Use gravity flow in plant layout where feasible to minimize the need for pumps or solids handling equipment for hazardous materials. Conduct a hazard review to assess the effect of layout on potential spills. 

Zinc oxide is usually contained in long, thin beds to lessen the chances of channeling. Pressure drop through the beds is low. Bed life is a function of gas H2S content and can vary from 6 months to in excess of 10 years. The spent catalyst is discharged by gravity flow and contains up to 20 weight percent of sulfur. 

G-25 M PP PE 1.5 9 28 Open Leur Taper Gravity Flow 0.15% Kathon CG DNA purification (>10 mers) 0.5-ml sample... 

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