Page 243 - APPLIED PROCESS DESIGN FOR CHEMICAL AND PETROCHEMICAL PLANTS, Volume 1, 3rd Edition
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Pumping of Liquids                                       21 5

                                                          Choice of leak-resistant packing or
                                                          standard mechanical seal (illustrated).
                                                          Special mechanical seals available to
      Positive-lock thrust control for preci-             fit equipment.               Integral safety relief valve works to
      sion rotor and shaft positioning to                                              protect system against excessive
      maintain original performance and                       I                                   I
      minimize wear for en











                   1
















                                                                     I         I
                                                   Cushioned, positive-flow action of   Specially designed and machined
                                                   rotor and idler combination provides   revolvable casing provides eight
                                                   non-pulsating, low-shear transmis-   port positions to suit application.
                                                   sion of liquid.
                     Figure 3-658. Typical rotary gear pump. (By permission, Viking Pump, Inc., Unit of ldex Corporation.)

      selection of these pumps, it is sometimes better to select a   Significant Features in Reciprocating Pump
      larger pump running at low speeds than a smaller pump   Arrangements
      at high speeds when dealing with viscous materials.
                                                              I. Liquid Pump End
         As  a general guide, speed is reduced 25-35  percent   A. Pump Pressure Component
      below rating for each tenfold increase in viscosity above    1. Piston
       1000 SSU. Also, generally, the mechanical efficiency of
       the  pump  is  decreased  10 percent  for  each  ten  fold   2. Plunger
      increase in viscosity above 1000 SSU, and referenced to   B. Types
      a maximum efficiency of 55 percent at this point.  [l]       1. Simplex, one piston
                                                                   2. Duplex, two piston (Figure 3-66)
                      Reciprocating Pumps                          3. Triplex, three piston (not used as steam driven)
                                                                C. Piston or Plunger Action
                                                                   1. Single acting, one stroke per rpm
         Reciprocating pumps are positive displacement pis-
       ton units driven  by  a direct connected  steam cylinder    2. Double  acting,  two  strokes per  rpm,  cylinder
                                                                     fills and discharges each stroke (Figure 3-67)
       or by an external power source connected to the crank-
       shaft of the pump piston. Being positive displacement,   D. Packing for Piston or Plunger
       these  pumps can  develop very high  pressures  (10,000     1. Piston packed: packing mounted on piston and
       psi and higher) for very low or high capacities  (up to       moves with piston; applied to comparatively  low
       1000 GPM) .                                                   pressures
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