Training - Flowserve Apm Pump Cw Pump Part4

Q&A

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Centrifugal Pump Basics Cavitation •If the pressure energy falls below the vapor pressure of a liquid, then vapor is formed. •Increase in volume from liquid to vapor depends on the liquid, temperature, and vapor pressure. ¾ 1 ft³ of water,, evaporated p at 212°F and 14.696 p psia,, becomes 1606 ft³ of dry saturated steam, (vapor).* •Vapor bubbles on their way through the pump re-condense or collapse when they reach regions of higher pressure

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Centrifugal Pump Basics Cavitation • Vaporization and the collapse of that vapor within a pump • Reduces pump performance. • Sustained Cavitation can cause damage to a pump.

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Centrifugal Pump Basics Net Positive Suction Head (NPSH) •NPSHA, is the head available in the system, taking into account friction loss in suction piping, valves, fittings etc. NPSHa should always be given in absolute values. •In all cases the NPSHA must exceed the NPSHR in order to push the liquid into the pump.

…… Vane “Top Edge”

Cavitation Bubbles

……  Impeller Outter Diameter Flowserve Corporation Property and Confidential

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Centrifugal Pump Basics Net Positive Suction Head Available Vapor pressure, absolute, ft Net Positive Suction Head Available

Static suction head, ft

Friction loss,, suction side,, ft

Surface pressure, ft

Atmospheric pressure, ft

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Centrifugal Pump Basics NPSHa on a System in Operation

Suction gauge pressure, ft

Elevation of gauge above pump centerline, ft

Suction velocity head, ft

Vapor pressure, absolute, ft

Atmospheric pressure, ft

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Centrifugal Pump Basics Net Positive Suction Head (NPSH) NPSHR is the head required by the pump to cover the losses in the pump suction - that is shown on the pump characteristic curve.

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Centrifugal Pump Basics Net Positive Suction Head Required •Varies with pump design, size, and operating conditions. •Requires testing for accurate determination.

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Centrifugal Pump Basics Classical Cavitation •Classical cavitation occurs when the absolute pressure of a moving liquid is reduced to, or even below the vapor pressure of the liquid in the impeller eye. •Bubbles are formed in the impeller eye.

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Centrifugal Pump Basics Classical Cavitation Somewhere along the low pressure side of the impeller vane, the pressure may once again exceed the vapor pressure and cause the bubbles to collapse.

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Centrifugal Pump Basics • The difference between NPSHA and NPSHR must be sufficiently large to reduce the formation of cavitation. • There should be a reasonable margin between NPSHA and NPSHR 9 General guidelines are that NPSH margin should be 5 ft. or 20% whichever is greater 9 HI has come up with a more specific guideline chart which is based on pump type and suction energy level

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Centrifugal Pump Basics Factors affecting NPSHA of a Piping System NPSH available should always be determined during the design of a pumping system. 1.When the pump is installed an appreciable height above the liquid level 2.When the pump takes suction from a tank under vacuum 3.When the liquid has a high vapor pressure

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Centrifugal Pump Basics Factors affecting NPSHA of a Piping System NPSH available should always be determined during the design of a pumping system. 4.When the suction line is unusually long 5.When the pumping system is at an altitude considerably above sea level ((lower atmospheric p p pressure))

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Centrifugal Pump Basics Methods to Increase NPSHa •Maintain a higher level of liquid at suction source •Physically raise the suction source – tank •Artificially increase the pressure on the surface of the liquid at the suction source

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Centrifugal Pump Basics Methods to Increase NPSHa •Reduce the vapor pressure of the liquid by cooling the suction source •Change the suction side piping 9 Pipe size 9 Valve types 9 Gaskets

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Centrifugal Pump Basics Methods to Reduce NPSHr •Reduce pump speed •Use pump with double suction first stage impeller •Use a vertical turbine type pump

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Centrifugal Pump Basics Recirculation Cavitation

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Centrifugal Pump Basics Recirculation Cavitation Damage is influenced by: •Impeller inlet tip speed •Degree to which recirculation is taking place •NPSH margin •Characteristics of the pumped liquid •Pump energy level •Materials of construction

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Centrifugal Pump Basics Real World Examples

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Centrifugal Pump Basics Real World Examples

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Q&A

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