Pump suction

To lessen the risk of pumping sludges or slurries into a unit, the practice is to leave a safety margin of 50 cm (heel) below the outlet nozzle or install a strainer on the pump suction line. The deposits accumulate with time and the tanks are periodically emptied and cleaned. 

The best results are obtained with freshly prepared xanthhydrol (reduction of xanthone with sodium amalgam. Section VII,16). Dissolve 0 -25 g. of xanthhydrol and 0 -25g. of the primary sulphonamide in 10 ml. of glacial acetic acid. Shake for 2-3 minutes at the laboratory temperature and allow to stand for 60-90 minutes. Filter oflf the derivative, recrystallise it from dioxan-water (3 1), and dry at room temperature under water pump suction for 30 minutes. 

Pump Suction. The net positive suction head required (NPSHR) affects the resistance on the suction side of the pump. If it drops to or near the vapor pressure of the fluid being handled, cavitation and loss of performance occurs (13). The NPSHR is affected by temperature and barometric pressure and is of most concern on evaporator CIP units where high cleaning temperatures might be used. A centrifugal booster pump may be installed on a homogenizer or on the intake of a timing pump to prevent low suction pressures. 

Makeup. Makeup water is the water suppHed to replenish the steam system for any losses. In most systems it is introduced into the condenser or the feed pump suction. In steam systems where the makeup is a small fraction of the total feedwater, its purity may be somewhat lower than the feedwater requirement because it is diluted by condensate. In systems where there is Httie condensate return, such as heating steam suppHes, the makeup purity must be essentially the same as the feedwater. 

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. 

Another parameter that helps in evaluating the pump suction limitations, such as cavitation, is suction specific speech... 

Typically, for single-suction pumps, suction-specific speed above 11,000 is considered excellent. Below 7000 is poor and 7000-9000 is of an average design. Similarly, for double-suction pumps, suction-specific speed above 14,000 is considered excellent, below 7000 is poor, and 9000-11,000 is average. 

Air leaks into the system if the pump suction is below atmospheric pressure. 

In a submerged-tube FC evaporator, all heat is imparted as sensible heat, resulting in a temperature rise of the circulating hquor that reduces the overall temperature difference available for heat transfer. Temperature rise, tube proportions, tube velocity, and head requirements on the circulating pump all influence the selec tion of circulation rate. Head requirements are frequently difficult to estimate since they consist not only of the usual friction, entrance and contraction, and elevation losses when the return to the flash chamber is above the liquid level but also of increased friction losses due to flashing in the return line and vortex losses in the flash chamber. Circulation is sometimes limited by vapor in the pump suction hne. This may be drawn in as a result of inadequate vapor-liquid separation or may come from vortices near the pump suction connection to the body or may be formed in the line itself by short circuiting from heater outlet to pump inlet of liquor that has not flashed completely to equilibrium at the pressure in the vapor head. 

Water from cooling tower pump suction, pH 8.6-8.8, pressure 20-30 psi (140-210 kPa), flow 2-5 ft/s (0.2 to 1.5 m/s). Dispersant, 1-3 ppm tolyltriazole, sodium hypochlorite 2 hr/day to 0.8 free residual chlorine 0.6-0.8 ppm total zinc and 0.1-0.2 ppm soluble zinc. Free chlorine maintained at 1 ppm for 5 consecutive days/month during the summer. Chemical treatment started after 2 years of no treatment. Water conductivity -612 ( imhos/cm), turbidity 27 NTU (nephelometric turbidity units), chloride 110 ppm, sulfate 50 ppm, carbonate alkalinity (CaCOa) 27 ppm, bicarbonate alkalinity (CaCOs) 118 ppm... 

The fluid arrives at the pump suction nozzle as it flows through the... 

To express the quantity of energt available in the lit]iiid entering into the pump, the unit of measure for NPSH is feet of head or elevation in the pump suction. The pump has its NPSHr, or Net Positive Suction Head Required. The system, meaning all pipe, tanks and connections on the suction side of the pump has the NPSHa, or the Net Positive Suction Head Available. There should always be more NPSHa in the system dian the NPSHr of the pump. Let s look at them, beginning with what the pump recgiires ... 

Hi Inlet Head. The los,ses in the pump suction throat to the impeller eye. These losses could be insignificant up to 2 ft, depending on design. 

Use an eccentric pipe reducer to connect to the pump suction nozzle (Figure 17-17). 

Oils, lubricating 6 fps Steel Pump suction lines 1-5 fps Steel... 

NPSH is the pressure available at the pump suction nozzle after vapor pressure is subtracted. It is expressed in terms of liquid head. It thus reflects the amount of head loss that the pump can sustain internally before the vapor pressure is reached. The manufacturer will specify the NPSH that his pump requires for the operating range of flows when handling water. This same NPSH is normally used for other liquids. 

The suction system piping should be kept as simple as reasonably possible and adequately sized. Usually the suction pipe should be larger than the pump suction nozzle. 

Use an eccentric reducer with the flat side up (to prevent trapping vapor) as the transition from the larger suction line to the pump suction nozzle. 

Kern, R., How to Design Piping for Pump-Suction Conditions, Chemical Engineering, April 28, 1975. 

NPSH calculations might have to be modified if there are significant amounts of dissolved gas in the pump suction liquid. See Suction System NPSH Available" in this handbook for calculations when dissolved gas does not need to be considered. In that case the suction liquid s vapor pressure is a term in the equation. With dissolved gases, the gas saturation pressure is often much higher than the liquid s vapor pressure. 

When circulating the blending system and running down into the tank at the same time, it may be possible to direct the rundown stream into the circulating pump suction for additional blending in the pump. 

Packing corroded away (twice). Poor separation. Pieces of packing in pump suction. Wrong metallurgy specification error. 

Oil pump suction plugged. mitted from the coupled 4. Shaft misalignment. 

Leak in oil pump suction piping. machine. To localize 5. Worn or damaged coupling. 

Branan, C. R., The Process Engineer s Pocket Handbook, Gulf Publishing Co., Houston, Texas, 1976. Kern, Robert, C. E. Refresher—How to Design Piping for Pump-Suction Conditions, Chem. Eng., April 28, 1975, p. 119. 

The pressurized lubrication system is a more elaborate lubrication method (.see Figure 3-19). The system has a main oil pump, either crankshaft or separately driven, a pump suction strainer, a cooler when needed, a... 

A strainer should be used in the pump suction line temporarily for a centrifugal pump and permanently for the rotary positive displacement pump. For the permanent installations, a Y-type strainer with an austenitic stainless strainer basket should be used. The cross-sectional... 

In 1997 it was reported that carbon-fibre reinforced PEEK had replaced aluminium in the fuel pump suction manifold of the Airbus. For this application the product has to withstand pressure thrusts of up to 30 bar and resist kerosene at operating temperatures in the range 40-200°C. The ventilation wheel for cooling the electric motor in the same application has also been converted from aluminium to PEEK. 

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