POSITIVE DISPLACEMENT PUMPS
DOE-HDBK-1018/1-93
Pumps
POSITIVE DISPLACEMENT PUMPS
Positive displacement pumps operate on a different principle than centrifugal
pumps. Positive displacement pumps physically entrap a quantity of liquid at the
suction of the pump and push that quantity out the discharge of the pump.
EO 2.1
STATE the difference between the flow characteristics of
centrifugal and positive displacement pumps.
EO 2.2
Given a simplified drawing of a positive displacement pump,
CLASSIFY the pump as one of the following:
a.
Reciprocating piston pump
b.
Gear-type rotary pump
c.
Screw-type rotary pump
d.
Lobe-type rotary pump
e.
Moving vane pump
f.
Diaphragm pump
EO 2.3
EXPLAIN the importance of viscosity as it relates to the
operation of a reciprocating positive displacement pump.
EO 2.4
DESCRIBE the characteristic curve for a positive
displacement pump.
EO 2.5
DEFINE the term slippage.
EO 2.6
STATE how positive displacement pumps are protected
against overpressurization.
Introduction
A positive displacement pump is one in which a definite volume of liquid is delivered for each
cycle of pump operation. This volume is constant regardless of the resistance to flow offered
by the system the pump is in, provided the capacity of the power unit driving the pump or pump
component strength limits are not exceeded. The positive displacement pump delivers liquid in
separate volumes with no delivery in between, although a pump having several chambers may
have an overlapping delivery among individual chambers, which minimizes this effect. The
positive displacement pump differs from centrifugal pumps, which deliver a continuous flow for
any given pump speed and discharge resistance.
Positive displacement pumps can be grouped into three basic categories based on their design
and operation. The three groups are reciprocating pumps, rotary pumps, and diaphragm pumps.
ME-03
Rev. 0
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