|
Pump Knowledge
Menu | Plunger Pump Suppliers
Plunger Pumps are reciprocating positive displacement pumps which are
generally configured in four ways: direct-acting or
indirect-acting; simplex or duplex; single-acting or
double-acting; and power pumps.
Some reciprocating pumps are powered by prime
movers that also have reciprocating motion, such
pumps are powered by a reciprocating steam piston or plunger. The
plunger rod of the steam piston may be directly connected to the
liquid piston of the pump or it may be indirectly connected
with a beam or linkage. Direct-acting piston pumps have a
plunger on the liquid ( pump ) end that is directly driven by the
pump rod ( also the piston rod or extension thereof ) and carries
the piston of the power end. Indirect-acting pumps are
driven by means of a beam or linkage connected to and actuated
by the power piston rod of a separate reciprocating engine.
A simplex plunger pump, sometimes referred to as
a single piston plunger pump, is a pump having a single liquid ( pump )
cylinder. A duplex plunger pump is the equivalent of two simplex type
pumps placed side by side on the same foundation. The driving
of the pistons / plungers of a duplex pump is arranged in such a manner
that when one piston is on its upstroke the other piston is on
its down stroke, and vice versa. This arrangement doubles the
capacity of the duplex pump compared to a simplex pump of
comparable design.
A single-acting plunger pump is one that takes a
suction, filling the pump cylinder on the stroke in only one
direction, called the suction stroke, and then forces the
liquid out of the cylinder on the return stroke, called the
discharge stroke. A double-acting plunger pump is one that, as
it fills one end of the liquid cylinder, is discharging liquid
from the other end of the cylinder. On the return stroke, the
end of the cylinder just emptied is filled, and the end just
filled is emptied. One possible arrangement for single-acting
and double-acting pumps is shown in Figure 13.
Power pumps convert rotary motion to low speed
reciprocating motion by reduction gearing, a crankshaft,
connecting rods and crossheads. Plungers are driven
by the crosshead drives. Rod and piston construction, similar
to duplex double-acting steam pumps, is used by the liquid ends
of the low pressure, higher capacity units. The higher pressure
units are normally single-acting plungers, and usually employ
three (triplex) plungers. Three or more plungers substantially
reduce flow pulsations relative to simplex and even duplex
pumps.
Power pumps typically have high efficiency and
are capable of developing very high pressures. They can be
driven by either electric motors or turbines. They are
relatively expensive pumps and can rarely be justified on the
basis of efficiency over centrifugal pumps. However, they are
frequently justified over steam plunger pumps where
continuous duty service is needed due to the high steam
requirements of direct-acting plunger steam pumps. In general, the
effective flow rate of plunger pumps decreases as the
viscosity of the fluid being pumped increases because the speed
of the pump must be reduced. In contrast to centrifugal pumps,
the differential pressure generated by plunger reciprocating pumps is
independent of fluid density. It is dependent entirely on the
amount of force exerted on the piston.
© Copyright 2000 - 2008, by Engineers Edge, All rights reserved. Disclaimer
|
