Reduced-flow

The spring ensures a soHd closing action and is usually wound from stainless steel wire. The dip tube conducts the product from the container to the valve. It is usually extmded from polyethylene or polypropylene and has an inside diameter of over 2.54 mm, although it can be provided in capillary sizes having diameters down to 0.25 mm. These small tubes are used to reduce flow rate and may function in place of the Hquid metering orifice in the valve housing. 

Fig. 7. Control of fan performance with inlet vane control. SoHd lines marked A and N show normal performance without vanes (vanes wide open). As vanes are progressively closed, static and power curves are modified as indicated by dashed lines. Intersection ( - ) of the system resistance curve with these reduced pressure curves at points B, C, D, and E shows how imparting more spin to the inlet air reduces flow. Projecting points A to E vertically downward to the corresponding power curve locates fan power points A through E7 Power savings achieved over throttling control can be estimated by projecting points B through E vertically downward to the A power curve and comparing the value with that from the proper reduced power curve. To...

Low Flow Operation. The optimum operation of a pump is near the best efficiency point. Some manufacturers curves indicate the minimum allowable continuous stable flow (MCSF) limits for every pump (43). In the 1980s, the processing industry experienced a reduction in flow requirement as a result of business downturn and installation capacity downsizing. The pumping equipment, however, was generally not replaced by smaller pumps, but was forced to operate at reduced flow rates, often below allowable MCSF. This has resulted in increased failure rates and reduced pump component life. 

There are two main reasons why a pump should not operate below its MCSF (/) the radial force (radial thmst) is increased as a pump operates at reduced flow (44,45). Depending on the specific speed of a pump, this radial force can be as much as 10 times greater near the shut off, as compared to that near the BEP and (2) the low flow operation results in increased turbulence and internal flow separation from impeller blades. As a result, highly unstable axial and radical fluctuating forces take place. 

Cavitation has three negative side effects in valves—noise and vibration, material removal, and reduced flow. The bubble-collapse process is a violent asymmetrical implosion that forms a high-speed microjet and induces pressure waves in the fluid. This hydrodynamic noise and the mechanical vibration that it can produce are far stronger than other noise-generation sources in liquid flows. If implosions occur adjacent to a solid component, minute pieces of material can be removed, which, over time, will leave a rough, cinderlike surface. 

Suction Limitations of a Pump Whenever the pressure in a liquid drops below the vapor pressure corresponding to its temperature, the liquid will vaporize. When this happens within an operating pump, the vapor bubbles will be carried along to a point of higher pressure, where they suddenly collapse. This phenomenon is known as cavitation. Cavitation in a pump should be avoided, as it is accompanied by metal removal, vibration, reduced flow, loss in efficiency, and noise. When the absolute suction pressure is low, cavitation may occur in the pump inlet and damage result in the pump suction and on the impeller vanes near the inlet edges. To avoid this phenomenon, it is necessary to maintain a required net positive suction head (NPSH)r, which is the equivalent total head of liquid at the pump centerline less the vapor pressure p. Each pump manufacturer publishes curves relating (NPSH)r to capacity and speed for each pump. 

Install larger suction piping or reduce flow through pump. 

Reduce flow to design rates. Raise liquid level in suction vessel. Install vortex breaker in suction vessel. 

Replace motor with one of larger size, or reduce flow rate. 

An emergency system water pipe section was removed because of reduced flow. In places, as much as 40% of the internal cross-sectional area was blocked by tubercular growth (Fig. 3.1). 

Figure 7-4. Reduced power versus reduced flow.

The invariant coordinate, qj., is used to determine the flow calculation independent of inlet conditions. To determine the reduced flow... 

Increase In absolute flow angle at exit with reduced flow... 

Continuous flow With continuous flow operations consider (e.g. using a HAZOP procedure) the effects of No flow Reduced flow Reverse flow Increased flow Contaminated flow Flow of a substituted material, etc. 

In this diagram the key features are A - Diffusion baffle this serves four roles. First to dissipate the velocity head, thereby improving the overall hydraulic characteristics of the separator. Next, to direct incoming flow downward and outward maximizing the use of the separator volume. Third, to reduce flow turbulence and to distribute the flow evenly over the separator s cross-sectional area. Finally, to isolate inlet turbulence from the rest of the separator. B- Internal chambers In the sediment chamber, heavy solids settle out, and concentrated slugs of oil rise to the surface. As the oily water passes through the parallel corrugated... 

J(S 1 Valve body track Loss of fluid to header Reduce flow redundant train Valve off use other train lL- 0/hr... 

Silica Si 0, Scale buildup on surrounding surfaces, reducing flow and heat transfer Removed by applying hot magnesium salts Demineralization processes... 

FIC8 = No Flow (new) Conditions are as specified. It must be inadequate cooling of column Top reflux pump failure (confirmed) Alternative goals Reduce heating in reboiler Reduce flow rate of input Increase cooling in condenser ... 

Less Less Flow Excess ammonia in reactor. Release to work area, with amount released related to quantitative reduction in supply. Team member to calculate toxicity vs. flow reduction. 1. Valve A partially closed. 2. Partial plug or leak in pipe. Automatic closure of valve B on reduced flow from phosphoric acid supply. Set point determined by toxicity vs. flow calculation. 

Similar considerations apply to best volume flow rates for samples of different molar mass. For high molar mass samples, flow rates should be reduced to avoid shearing the macromolecule in the column. Moreover, a reduced flow rate is necessary because the diffusion coefficients of large molecules will get pretty small. This means that the macromolecule will pass by a pore in the packing material without having the time to enter it, if the linear flow rate is too high. 

The optimum flow rate for most SEC separations using conventional PLgel column dimensions (internal diameter 7.5 mm) is 1.0 ml/min. It may be of some benefit to work with lower flow rates, particularly for the analysis of higher molecular weight polymers where the reduced flow rate improves resolution through enhanced mass transfer and further reduces the risk of shear... 

The reduced flow rates given by Equation (12) are thus ... 

Example If the shell-side coefficient of a unit is 25 Btu/hr (ft )(°F) and velocity in the shell is doubled, read the new shell-side coefficient, h as 36 (line a). If the tube-side coefficient is 25 and velocity is doubled, read the new tube coefficient, h, as 43.1 (line a). In other cases, pressure drop would increase by a factor of 4. Note This may be used in reverse for reduced flow. 

If pressure drop is too high, reselect and redesign unit, making parallel units to reduce flow rate (and coefficient hi ), or select a larger pipe, reducing mass rate G, and hence hj. Recalculate the pressure drop. 

The power consumption remains constant for this type of operation thus, no savings are effected hy a reduced flow. The pumping point remains unchanged as contrasted to a reduced point for inlet throtding. 

Pressure drop under streamline flow conditions is directly proportional to the quantity of oil flowing. The effect of reduced flow rate after take-off points, as compared with full flow rate throughout the full length of the pipeline when there is no take-off, should be taken into account to ensure that variation in pressure is within the specified pump output. Special consideration is necessary with gravity and ring main systems serving several take-off points. 

Since no serious problems exist with corrosion, the materials of constmction can be cheaper and the thicknesses reduced. Fouling coefficients do not need to be incorporated into the design calculations, as the surfaces remain clean indefinitely. This in itself provides a secondary benefit in that the pitching of fins may be reduced without the risk of reducing flow. 

A greater difficulty arises where the compressor may go down to 33% or 25% capacity and the thermostatic expansion valve is called upon to control a much reduced flow Under such conditions, the thermostatic expansion valve maybe unstable and hunt , with slight loss of evaporator efficiency Since the required duty is less, this is of no great importance. It is possible to fit two expansion valves in parallel, one for the minimum load and both for the full load, but this arrangement is not usually necessary... 

It is controlled by changing the gate to direct the material to a nearby wall to slow the initial flow, by changing the size of the gate to reduce flow rate, by changing the shape... 

The effect of carryover and after-precipitation is that solids settle out and cause pre-boiler system fouling and result in reduced flow and equipment waterway blockages. Check valves are especially prone to blockage. 

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