pumps

• if the head is very small, if the edge is well rounded, or if air cannot flow in beneath the nappe, this results in an increase in the discharge rate for a given head as compared with that for a free nappe
• Narrow rectangular notches have been found to give about 93 percent of the discharge predicted by the Francis formula
• For the flow of high-viscosity liquids over rectangular weirs, the discharge decreases markedly for a given head as viscosity is increased
• For fluids of moderate viscosity, the effect of viscosity and surface tension on the discharge flow rate for rectangular and triangular-notch ( 45°) weirs can be neglected when (NR) 0.2 (Nwe) 0.6 > 900
• Standards governing pumps and compressors

  • ASME Standards
  • API Standards
  • Hydraulic Institute Standards
  • NFPA Standards
• Pumps and compressors


  • Used to deliver fluids from one location to another through conduits
  • Pump is used when the fluid is a liquid, compressor is used when the fluid is a gas
• 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
• Major types of pumps

  • Positive displacement
  • Dynamic (kinetic)
  • Lift
  • Electromagnetic
• 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 is variable
  • Mechanical considerations limit maximum throughputs
  • Capable of efficient performance at extremely low-volume throughput rates
• Centrifugal fluid-transport devices


  • Discharge is relatively free of pulsation
  • Mechanical design lends itself to high throughputs
  • 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 pumps


  Use electromagnetic field around the fluid conduit to create a driving force that will cause flow
• Jets and eductors


  Deceleration of one fluid (motivating fluid) to transfer its momentum to a second fluid (pumped fluid)
• Turbine or regenerative-type pump


  Functions partially by mechanical impulse
• Capacity


  Mass rate of fluid flow through the pump/compressor
• Head


  Total pressure differential measured immediately before and after the pump/compressor, usually expressed in the height of column of fluid equivalent under adiabatic conditions
• Pump capacity


  The product of (1) the mass rate of fluid flow through it 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
• Capacity


  The first of the two quantities that determine pump capacity, normally referred to as capacity
• Head


  The second of the two quantities that determine pump capacity, known as head
• 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 (ha) minus the total suction head (hs)
• Total Suction Head (hs)


  The reading (has) of a gauge at the suction flange of a pump (corrected to the pump centerline), plus the barometer reading and the velocity head (hvs) at the point of gauge attachment
• Static Suction Head (hss)


  The vertical distance measured from the free surface of the liquid source to the pump centerline plus the absolute pressure at the liquid surface
• Total Discharge Head (hd)


  The reading (hgd) of a gauge at the discharge flange of a pump (corrected to the pump centerline), plus the barometer reading and the velocity head (hvd) at the point of gauge attachment
• Static Discharge Head (hsd)


  The vertical distance measured from the free surface of the liquid in the receiver to the pump centerline, plus the absolute pressure at the liquid surface
• Velocity


  The relationship between the quantity flowing past a given point in a given time and the velocity of flow for incompressible liquids
• Velocity Head


  The vertical distance by which a body must fall to acquire the velocity v
• Viscosity


  The internal friction or internal resistance to relative motion of the fluid particles in flowing liquids
• Viscosity of liquids usually decreases with rising temperature
• Viscous liquids tend to increase the power required by a pump, reduce pump efficiency, head, and capacity, and increase friction in pipe lines
• Friction Head


  The pressure required to overcome the resistance to flow in pipe and fittings
• Work Performed in Pumping

  The energy imparted to the liquid in performing the service required of the pump, which must be accounted for
• Pump Efficiency


  The ratio of power output to power input, defined as (power output)/(power input)
• When selecting pumps, it is necessary to know the liquid to be handled, the total dynamic head, the suction and discharge heads, and often the temperature, viscosity, vapor pressure, and specific gravity
• In the chemical industry, pump selection is frequently further complicated by the presence of solids in the liquid and liquid corrosion characteristics requiring special materials of construction
• Positive Displacement Pumps


  • Provide high heads at low capacities, suited for high-viscosity service and slurry