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NPSHr required

NPSH reductions should be limited to 50% of the NPSHr required by the pump for cold water, which is the fluid basis of the manufacturer s NPSHr curves. [Pg.192]

The NPSHr required at the higher temperature may become the controlling factor if cavitation is noL Lo occur. [Pg.209]

NPSHR at the rated point shall not exceed the quoted value (see Table 4-2). Dismanthng to correct NPSHR requires a retest (see 4.3.3.4.2). [Pg.54]

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. [Pg.361]

It is difficult to determine exactly the areas of localized pressure reductions inside the pump, although much research has been focused on this field. It is easy, however, to measure the total fluid pressure (static plus dynamic) at some convenient point, such as pump inlet flange, and adjust it in reference to the pump centerline location. By testing, it is possible to determine the point when the pump loses performance appreciably, such as 3% head drop, and to define the NPSH at that point, which is referred to as a required NPSH (NPSHR). The available NPSH (NPSHA) indicates how much suction head... [Pg.290]

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 ... [Pg.13]

This ty pe of cavitation is also called inadequate NPSHa cavitation. To prevent this ty pe of cavitation, the NPSHa in the system (the available energ) in the system), must be higher than the NPSHr of the pump (the pump s minimum energy requirement). [Pg.29]

Wliere N = the speed of the pump/motor in revolutions per minute Q = the square root of the flow in gallons per minute at the Best Efficiency Point BEP. For double suction pumps, use A BEP Flow. NPSHr = the net positive suction head required by the pump at the BFiP. [Pg.67]

The Pump s Minimum Rec]uirement Curve. Its ealled Net Positive Suction Head required, NPSHr. [Pg.76]

Figures 3-36A, 3-36B, and 3-36C represent typical and actual performance curves showing discharge total head (head pressure at pump outlet connection for any fluid), required minimum water horsepow er (for pumping water), and capacity or pumping volume of the pump (for any fluid) for several impeller diameters that would fit the same case (housing). In addition the important NPSHr (net positive suction head required by the pump) charac-... Figures 3-36A, 3-36B, and 3-36C represent typical and actual performance curves showing discharge total head (head pressure at pump outlet connection for any fluid), required minimum water horsepow er (for pumping water), and capacity or pumping volume of the pump (for any fluid) for several impeller diameters that would fit the same case (housing). In addition the important NPSHr (net positive suction head required by the pump) charac-...
Figure 3-36A represents a typical manufacturer s performance curve. The values of NPSHr given are the minimum values required at the pump suction. As mentioned, good practice requires that the NPSH available be at least two feet of liquid above these values. It is important to recognize that the NPSHr and Suction Lift Values are for handling water at about 70°F. To use with other liquids it is necessary to convert to the equivalent water suction lift at 70°F and sea level. [Pg.190]

Absolute pressure at the pump inlet must not be low enough to release non-condensables of (2). If such release can occur, then the NPSHr would need to be increased above that of the cold water requirements to avoid cavitation and poor pump performance. [Pg.192]

Assume that a boiler feed water is being pumped at 180 °F. Read the chart in Figure 3-46 and the water vapor pressure curve, and follow over to read NPSH reduction = 0.45 feet. A pump selected for the sertice requires 6 feet cold water service NPSHr ... [Pg.194]

Example 3-6 NPSH Available in Vacuum System, 191 Example 3-7 NPSH. Available in Pressure System, 191 Example 3-8 Closed System Steam Surface Condenser NPSH Requirements, 191 Example 3-9 Process Vacuum System, 192 Reductions in NPSHr, 192 Example 3-10 Corrections to NPSHr for Hot Liquid Hydrocarbons and Water. 192 Example 3-9 Process Vacuum System, 192 Example 3-10 Corrections to NPSHr for Hot Liquid Hydrocarbons and Water, 192 Example 3-11 Alternate to Example 3-10, 194 Specific Speed,... [Pg.641]

This is a statement of the NPSH that the pump can sustain by its own operation, so that the operating requirement is that NPSHr > NPSHa- NPSHr is more difficult than NPSHa to determine. Reference 7 suggests working relations for positive displacement machines that are outlined below. [Pg.507]

Figure 32.53 gives a typical plot of cr against ks that may be used as a first design estimate of NPSHr, but in many applications, test data are required... [Pg.507]

To prevent cavitation, it is necessary that the pressure at the pump suction be sufficiently high that the minimum pressure anywhere in the pump will be above the vapor pressure. This required minimum suction pressure (in excess of the vapor pressure) depends upon the pump design, impeller size and speed, and flow rate and is called the minimum required net positive suction head (NPSH). Values of the minimum required NPSH for the pump in Fig. 8-2 are shown as dashed lines. The NPSH is almost independent of impeller diameter at low flow rates and increases with flow rate as well as with impeller diameter at higher flow rates. A distinction is sometimes made between the minimum NPSH required to prevent cavitation (sometimes termed the NPSHR) and the actual head (e.g., pressure) available at the pump suction (NPSHA). A pump will not cavitate if NPSHA > (NPSHR + vapor pressure head). [Pg.248]

NPSHR = net positive suction head required (see 1.4.27) in meters... [Pg.18]

When liquids are being pumped, it is important to keep the pressure in the suction line above the vapor pressure of the fluid. The available head measured at the pump suction is called the net positive suction head available (NPSHA). At sea level, pumping 15°C (60°F) water with the impeller about 1 m below the surface, the NPSHA is about 9.1 m (30 ft). It increases with barometric pressure or with static head, and decreases as vapor pressure, friction, or entrance losses rise. Available NPSHA is the characteristic of the process and represents the difference between the existing absolute suction head and the vapor pressure at the process temperature. The required net positive suction head required (NPSHR), on the other hand, is a function of the pump design (Figure 2.121). It represents the minimum margin between suction head and vapor pressure at a particular capacity that is required for pump operation. Cavitation can occur at suction pres-... [Pg.301]

P030 NPSH Required at Rated Capacity NPSHR RATE N 13 m... [Pg.37]


See other pages where NPSHr required is mentioned: [Pg.13]    [Pg.84]    [Pg.21]    [Pg.146]    [Pg.13]    [Pg.84]    [Pg.21]    [Pg.146]    [Pg.301]    [Pg.303]    [Pg.31]    [Pg.82]    [Pg.82]    [Pg.86]    [Pg.160]    [Pg.1347]    [Pg.160]    [Pg.189]    [Pg.800]    [Pg.183]    [Pg.17]    [Pg.159]    [Pg.161]    [Pg.101]   


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Net positive suction head required NPSHr)

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