Momentra

• q


  Volume flow rate
• g


  Local acceleration due to gravity
• A pump or compressor is a physical contrivance that is used to deliver fluids from one location to another through conduits
• Pump


  Used when the fluid is a liquid
• Compressor


  Used when the fluid is a gas
• Basic requirements to define the application

  • Suction and delivery pressures
  • Pressure loss in transmission
  • Flow rate
• Special requirements may exist in food, pharmaceutical, nuclear, and other industries that impose material selection requirements of the pump
• Primary means of transfer of energy to the fluid that causes flow

  • Gravity
  • Displacement
  • Centrifugal force
  • Electromagnetic force
  • Transfer of momentum
  • Mechanical impulse
  • Combination of these energy-transfer mechanisms
• Displacement and centrifugal force are the most common energy-transfer mechanisms in use
• Pumps and compressors are designed per technical specifications and standards developed over years of operating and maintenance experience
• Standards governing pumps and compressors

  • ASME Standards
  • API Standards
  • Hydraulic Institute Standards
  • NFPA Standards
• Major types of pumps

  • Positive displacement
  • Dynamic (kinetic)
  • Lift
  • Electromagnetic
• Piston pumps are positive displacement pumps
• The most common centrifugal pumps are of dynamic type
• Ancient bucket-type pumps are lift pumps
• Electromagnetic pumps use electromagnetic force and are common in modern reactors
• Canned pumps are also becoming popular in the petrochemical industry because of the drive to minimize fugitive emissions
• Displacement


  Discharge of a fluid from a vessel by partially or completely displacing its internal volume with a second fluid or by mechanical means
• Displacement-type fluid-transport devices


  • Adaptable to high-pressure operation
  • Flow rate through the pump is variable
  • Mechanical considerations limit maximum throughputs
  • Capable of efficient performance at extremely low-volume throughput rates
• Centrifugal force


  Applied by means of the centrifugal pump or compressor
• Centrifugal fluid-transport devices


  • Discharge is relatively free of pulsation
  • Mechanical design lends itself to high throughputs, capacity limitations are rarely a problem
  • Capable of efficient performance over a wide range of pressures and capacities even at constant-speed operation
  • Discharge pressure is a function of fluid density
  • Relatively small high-speed devices and less costly
• Axial-flow compressor or pump


  Combines the use of centrifugal force with mechanical impulse to produce an increase in pressure
• Electromagnetic force


  Used when the fluid is an electrical conductor, as is the case with molten metals, to impress an electromagnetic field around the fluid conduit in such a way that a driving force that will cause flow is created
• Transfer of momentum


  Deceleration of one fluid (motivating fluid) in order to transfer its momentum to a second fluid (pumped fluid)
• Jets and eductors


  • Absence of moving parts and simplicity of construction
  • Relatively inefficient devices
  • When air or steam is the motivating fluid, operating costs may be several times the cost of alternative types of fluid-transport equipment
  • Environmental considerations in today's chemical plants often inhibit their use
• Mechanical impulse


  Usually combined with one of the other means of imparting motion, as in the case of axial-flow compressors and pumps, and the turbine or regenerative-type pump
• Capacity


  The mass rate of fluid flow through a fluid-transport device
• Head


  The total pressure differential measured immediately before and after the fluid-transport device, usually expressed in the height of column of fluid equivalent under adiabatic conditions
• Capacity (SI units)


  Cubic meters per hour (m³/h) for both liquids and gases
• Capacity (U.S. customary units)

  U.S. gallons per minute (gal/min) for liquids and in cubic feet per minute (ft³/min) for gases
• When gases are being handled, capacity must be related to a pressure and a temperature, usually the conditions prevailing
• Measurement of Performance


  The product of (1) the mass rate of fluid flow through a fluid-transport device and (2) the total pressure differential measured immediately before and after the device, usually expressed in the height of column of fluid equivalent under adiabatic conditions
• Head


  The total pressure differential measured immediately before and after a fluid-transport device, usually expressed in the height of column of fluid equivalent under adiabatic conditions
• Capacity is expressed in cubic meters per hour (m³/h) for both liquids and gases in SI units, and in U.S. gallons per minute (gal/min) for liquids and in cubic feet per minute (ft³/min) for gases in U.S. customary units
• Density or specific gravity must be used for conversion to mass rate of flow when using volume units for capacity
• For gases, capacity must be related to a pressure and a temperature, usually the conditions prevailing at the machine inlet
• All heads and other terms are expressed in height of column of liquid
• Total Dynamic Head (H)


  The total discharge head (hd) minus the total suction head (hs)
• Total Suction Head (hs)


  The reading of a gauge at the suction flange of a pump (corrected to the pump centerline), plus the barometer reading and the velocity head (hes) at the point of gauge attachment
• If the gauge pressure at the suction flange is less than atmospheric, the reading of a vacuum gauge is used for hgs with a negative sign