Page 150 - Fluid mechanics, heat transfer, and mass transfer

128 PUMPS, EJECTORS, BLOWERS, AND COMPRESSORS

➢ Triplex: Three pistons. Not used as steam-driven
pumps.
& Piston/Plunger Action:
➢ Single acting: One stroke per revolution.
FIGURE 5.22 Valve action for a double-acting reciprocating ➢ Double acting: Two strokes per revolution.
piston pump. ➢ Cylinder fills and discharges per each stroke.
& Packing for Piston/Plunger:
➢ Piston type: Piston packed in which packing is
& Figure 5.22 shows valve action for a double-acting
mounted on the piston and moves with it.
reciprocating piston pump.
➢ Plunger type: Cylinder packed in which packing is
& Figure 5.23 shows discharge curves for different flow
stationary and plunger moves; Expensive than
configurations for a reciprocating piston pump.
piston packed.
& Flow fluctuations are reduced, as illustrated in the
. What is a duplex pump?
above figures, from single-acting piston type,
& Reciprocating pump with two cylinders is called
through simplex double-acting-type, to duplex dou-
ble-acting-type pumps. duplex pump.
. What are the variations/arrangements involved in re- . What are the applications of (i) piston pumps and
ciprocating pump systems? (ii) plunger pumps?
& Pistonpumps:Usedforcomparativelylowerpressures,
& Main Pump Components: (i) Piston is used for low-
pressure light duty or intermittent service, which is light duty and intermittent service; less expensive than
less expensive than the plunger design, but cannot plunger pumps; and cannot handle gritty liquids.
handle gritty liquids. (ii) Plunger is used for high- & Plunger pumps: Used for high pressures, heavy duty,
pressure heavy duty or continuous service, which is andacontinuousoperation;expensivethanpistontype;
suitable for gritty and foreign material service. and can handle liquids with gritty/foreign material.
Expensive than the piston design. . “The flow rate in a positive displacement pump de-
& Types: creases significantly as the head increases.” True/
➢ Simplex: One piston. False?
➢ Duplex: Two pistons. & False.

FIGURE 5.23 Discharge curves for different reciprocating flow configurations.