System One PumpsSelecting Centrifugal Pumps

S1-201

• Head/Capacity• Temperature• Viscosity• Density• Vapor Pressure• Solids Content• Chemical

Compatibility• Multiple conditions

System One PumpsOperating Parameters

Remember…

The system controls the

pump.

System One PumpsHead/Capacity

THE SYSTEM

• As the rate of flow is increased through the system, friction losses increase.

• The losses increase discharge head and reduce suction head.

• This increases Total Dynamic head (TDH) as flow is increased.

THE PUMP

• The pump is a machine that is capable of producing a maximum amount of head at shutoff.

• As more of the pump’s energy is diverted to producing flow, less head is produced by the pump.

• The positive relationship between flow and head is the basis for the upward slope of the SYSTEM CURVE.

System One PumpsHead/Capacity 2

THE SYSTEM THE PUMP

• The tradeoff between head and flow is the basis for the downward slope of the HEAD/CAPACITY CURVE for the pump.

System One PumpsHead/Capacity 3

THE SYSTEM

• The system often changes.

• Open/close a valve.• Add/remove restrictions.• Levels in tanks change.• Filters get clogged.• Things get moved

around.

THE PUMP

• The pump is usually fixed.

• Impeller trim is set at assembly (can only be changed by disassembly or increased with new impeller.)

• Motor speed is fixed (unless VFD is employed.)

System One PumpsTemperature

THE SYSTEM

• It can change the density, viscosity, and vapor pressure of the pumped fluid, thus changing the shape of the system curve.

• The above factors can also impact NPSHa.

THE PUMP

• It can exceed the design limits of the pump or impact material selection.

• It can reduce lubricity of the pumped fluid.

• It can trigger the need for certain options.

• It can impact required clearances.

System One PumpsViscosity

THE SYSTEM

• Increases friction head• Increases required pipe

size. Or is the cause of problems if size is not increased.

• May or may not be constant in the system compared to at rest.

THE PUMP

• Shifts head/capacity curve down.

• Shifts power curve up.• Reduces efficiency.• Above 500cps has large

impact on efficiency.• About 1000cps is

practical limit.

System One PumpsDensity

THE SYSTEM

• Used to calculate head if only pressure is given.

• Impacts velocity head.

THE PUMP

• No impact on head/capacity.

• Impacts power requirements proportionally.

System One PumpsVapor Pressure

THE SYSTEM

• Can be important factor in determining NPSHa.

• Often not given in data• Need to know VP if other

factors point to low NPSHa.

• Need to know VP if fluid is unfamiliar.

• Need to know VP if temperature is high.

THE PUMP

• Pump will cavitate if NPSHa is less than NPSHr.

• In severe situations, can vapor lock the pump so nothing gets pumped.

System One PumpsSolids Content

THE SYSTEM

• Clogging will change shape of system curve.

• Abrasives may damage components, changing the shape of the system curve.

• Strainer can effect NPSHa.

THE PUMP

• Solids must fit through the smallest passage.

• Abrasives may impact material choice.

• Abrasives may dictate slower running speed.

• Can build up in close clearances or can jam the pump causing damage.

System One PumpsChemical Compatibility

THE SYSTEM

• Material selection.• Corrosion can reduce

pipe diameter, thus changing the shape of system curve.

THE PUMP

• Material selection.• Seal selection.• Seal support system

selection.

System One PumpsMultiple Conditions

THE SYSTEM

• Can be on one system curve. (Different flow through the same system.)

• Usually not on same system Curve. (System has been changed.)

THE PUMP

• If on same system curve, a variable speed drive may allow multiple conditions with one pump.

• If not, may not be possible with one pump and bypass loops, control valves, and/or VFD may be required.

System One pumps

Using Curves

Remember…

The system controls the

pump.

System One PumpsThe System Curve

• Shape is determined by physical elements of the system and the pumped fluid.

• Always parabolic.• Determined by any

two points on curve.• Operation can only be

on curve unless system is changed.

System One PumpsThe Head/Capacity Curve

• Shows tradeoff between head and flow.

• Each curve is for a fixed pump speed and impeller diameter.

• The pump can only operate on the H/C curve unless speed or diameter is changed.

System One PumpsThe Rated Duty

• The pump must operate somewhere on the H/C curve.

• The system controls where on the H/C curve the pump will operate.

• The actual duty is at the intersection of the two curves.

System One PumpsSelection Example

• 135 GPM (30.7 m³/hr)• 42 ft TDH (12.8m)• 68° F (20° C)• 1 cps• S.G. = 1• No Solids• Water

Design Flow, Confirm UnitsMaximum at design flowMaximum, Rated, MinimumThrough pump, not at restAt rated temperature

If present, get size, hardness, concentrationGet name of fluid to verify other data and make material selection.

System One PumpsCurve 1

System One PumpsCurve 2

System One PumpsCurve 3

System One PumpsCurve 4

System One PumpsCurve 5

System One PumpsCurve 6

System One PumpsCurve 7

System One PumpsApplication Information to Pump Datasheet

System One PumpsA Quote for Your Quotes:

“Default values have been used for all data not provided to Blackmer. Please review Pump Performance Datasheet to confirm that default values used are reasonable for the intended service.”

System one pumpsGeneral Arrangement Drawings

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