PUMP 101

The Key to Picking the Perfect Pump for the Job

With the right information, our sales representatives can quote a pump to more precisely fit your needs.

Just let us know the following, and we'll suggest the best pump model for you:

  • Fluid name, concentration, specific gravity, viscosity, solids data, temperature, flammability
  • Total dynamic head (TDH) and flow required
  • NPSHa (Net Positive Suction Head available)
  • Description of application
  • Customer experience with suitable materials of construction

Please hover over the tiles below for a brief Pump 101 tutorial and the factors that influence pump selection.

Fluid Name & Concentration

  • Critical to deciding materials of construction for the pump
  • If fluid is a trade name refer to MSDS (Material Safety Data Sheet)
  • Chemical resistance can vary with concentration and temperature

Specific Gravity

  • Specific Gravity is the weight of a given liquid compared to the weight of the equivalent volume of water.
  • By definition, water has a specific gravity of 1.0, but many chemicals have specific gravities greater than 1.0.
  • Many solvents and petroleum distillates have a specific gravity less than 1.0.

Viscosity

  • Viscosity is a measure of the resistance of a liquid to flowing.
  • It is needed to: Calculate friction loss in piping system
  • It is needed to: Correct the pump curve
  • Common units are cP (centiPoise) & cSt (centiStoke).

Flammable Fluids

  • Extreme care must be taken when applying a pump for flammable fluids
  • Use only pumps with stainless steel construction, DB Series with PVDF construction or UC Series
  • Use only explosion proof motors
  • Use with bronze bump ring centrifugal pump option where available
  • Make sure all components are grounded & bonded

Flow

  • Flow rate is the volume of liquid that needs to be pumped
  • It can be expressed as GPM (gallons per minute) or metric units like m3/hr (cubic meters per hour) or lpm (liters per minute)
  • Flow rate is required to calculate friction loss in the users piping system

Head

  • Frequently called TDH (Total Dynamic Head)
  • It is the discharge head minus the suction head or plus the suction lift.
  • Based on the piping system
  • Along with flow rate, needed to choose a pump from published curves
  • Expressed as feet or meters

Suction Head

  • Suction head exists when the liquid supply to the pump is ABOVE the pump
  • Equal to the static height in feet or meters that the liquid supply level is above the pump centerline less suction line losses
  • Commonly referred to as a “flooded suction” application

Suction Lift

  • Suction lift exists when the liquid supply to the pump is BELOW the pump.
  • Equal to the static height in feet or meters that the liquid supply is below the pump centerline less suction line losses
  • Generally, this type of application requires a self-priming pump like our SP Series

Discharge Head

  • Discharge head is comprised of:
  • Static discharge head
  • Frictional loss in pipe and fittings in discharge piping
  • Pressure in discharge container (if any)
  • Any loss at sudden enlargements
  • Exit loss

System Head

  • System curve is a plot of the head required to make liquid flow through piping system
  • A centrifugal pump always operates at intersection of head-capacity curve and system curve
  • System curve consists of: Static head Pressure head Friction loss in pipe & fitting

Net Positive Suction Head (NPSH)

  • Net Positive Suction Head (NPSH) is the suction head required by the pump and provided by the piping system to avoid cavitation
  • Called ‘net’ because the vapor pressure is always subtracted out, therefore it is over and above or ‘net of’ the vapor pressure
  • Called ‘positive’ because the units are always in absolute pressure terms – either feet-absolute or meters-absolute

Cavitation

  • Caused when the NPSHa is lower than the NPSHr required by the pump
  • Cavitation bubbles are formed in the low pressure region and rapidly collapse when entering higher pressure regions in the pump, causing erosion damage
  • More likely with hot fluids, fluids with high vapor pressures, suction sources that are under reduced pressure (vacuum) or larger impellers operating near full flow

Temperature

  • Maximum ambient temperature: usually based on motor maximum temperature
  • Minimum ambient temperature: usually based on pump materials of construction

Altitude

  • Higher altitudes:
  • Reduce lift capability
  • Reduce NPSHa
  • Affect motor by reducing cooling from the motor’s fan

Atmosphere

  • Hazardous atmospheres: follow guidelines for pumping flammables
  • Corrosive vapor filled atmospheres: consider chemical duty motor
  • Washdown areas: consider wash down duty motor
  • High humidity: consider tropical duty motor
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