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Suction Limitations of a Pump

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. [Pg.901]

There is a significant limitation on punp operation called Net Positive Suction Head (NPSH). Its origin is as follows. Although the effect of a pump is to raise the pressure of a liquid, frictional losses at the... [Pg.591]

You can only raise a column of cold water in a pipe a maximum of. S.S.9 ft with a pump in suction lift. Beyond 34 ft, the water will boil or vaporize. This is the reason why submersible pumps and vertical turbine pumps exist. I here is no limit to the distanee you can push a liquid from below, but you can only a.spirate a liquid a maximum of 34 ft from below the pump. [Pg.27]

The theoretical maximum suction lift at sea level for water (14.7 psi) (2.31 fi/psi) = 34 ft. However, due to flow resistance, this value is never attainable. For safety, 15 feet is considered the practical limit, although some pumps will lift somewhat higher columns of water. WTen sealing a vacuum condition above a pump, or the pump pumps from a vessel, a seal allowance to atmosphere is almost always taken as 34 feet of water. High suction lift causes a reduction in pump capacity, noisy operation due to release of air and vapor bubbles, vibration and erosion, or pitting (cavitation) of the impeller and some parts of the casing. (The extent of the damage depends on the materials of construction.)... [Pg.187]

When a pump is taking its suction from a tank, it should be located as close to the tank as possible in order to reduce the effect of friction losses on the NPSH available. Yet the pump must be far enough away from the tank to ensure that correct piping practice can be followed. Using a larger diameter line to limit the linear velocity to a level appropriate to the particular liquid being pumped can usually reduce pipe friction. Many industries work with a maximum velocity of about 5 feet per second, but this is not always acceptable. [Pg.522]

What is the upper limit of specific speed and capacity of a 1750-r/min single-stage double-suction centrifugal pump having a shaft that passes through the impeller eye if it handles clear water at 85°F (302 K) at sea level at a total head of 280 ft with a 10-ft suction lift What is the efficiency of the pump and its approximate impeller shape ... [Pg.206]

Operational constraints The various types of equipments used in a chemical plant have constraints inherent to their operation. Such constraints should be satisfied throughout the operation of a plant. For example, pumps must maintain a certain net positive suction head tanks should not overflow or go dry distillation columns should not be flooded the temperature in a catalytic reactor should not exceed an upper limit since the catalyst will be destroyed. Control systems are needed to satisfy all these operational constraints. [Pg.369]

In Chapter 14 the use of additives to combat potential fouling was discussed. In the use of chemical treatment for cooling water there has to be an emphasis on effective and rapid dispersion since the concentration of the additives employed must be low, i.e. a few mg/l where possible, to minimise cost and to reduce potential pollution problems. In general the additive formulation will be based on the need to limit corrosion (i.e. the use of corrosion inhibitors), scale formation (i.e. the use of crystal modifiers, dispersants or threshold chemicals or a combination) and biofouling (i.e. the use of biocides and dispersants). In many installations additives are injected on the suction side of the main pump so that turbulence within the pump will provide rapid mixing. In very large cooling systems multiple injection nozzles will be required to enhance distribution. [Pg.417]


See other pages where Suction Limitations of a Pump is mentioned: [Pg.879]    [Pg.702]    [Pg.1035]    [Pg.1038]    [Pg.883]    [Pg.879]    [Pg.702]    [Pg.1035]    [Pg.1038]    [Pg.883]    [Pg.186]    [Pg.426]    [Pg.113]    [Pg.291]    [Pg.300]    [Pg.302]    [Pg.1688]    [Pg.485]    [Pg.167]    [Pg.21]    [Pg.99]    [Pg.137]    [Pg.220]    [Pg.301]    [Pg.208]    [Pg.230]    [Pg.1509]    [Pg.137]    [Pg.131]    [Pg.302]    [Pg.137]    [Pg.137]    [Pg.237]    [Pg.2013]    [Pg.152]    [Pg.137]    [Pg.78]    [Pg.445]    [Pg.195]    [Pg.203]    [Pg.2001]    [Pg.1692]    [Pg.14]    [Pg.550]   


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