Figure 3-7.Gear-type rotary pump.
to minimize slippage from the discharge side back to
the suction side. They are designed to operate at
relatively moderate speeds. Operating at high speeds
causes erosion and excessive wear which results in
There are numerous types of rotary pumps and
various methods of classification. They may be
classified by shaft positioneither vertically or
horizontally mounted; the type of driveelectric
motor, gasoline engine, and so forth; their
manufacturers name; or service application. However,
classification of rotary pumps is generally made
according to the type of rotating element.
reciprocating is defined as back-and-forth motion. In a
reciprocating pump, it is the back-and-forth motion of
pistons inside of cylinders that provides the flow of
fluid. Reciprocating pumps, like rotary pumps, operate
on the positive principle; that is, each stroke delivers a
definite volume of liquid to the system.
The most common type of reciprocating pump is
the hand pump (fig. 3-13). There are two types of
manually operated reciprocating pumpssingle
action and double action. The single-action pump
provides flow during every other stroke, while the
double-action provides flow during each stroke.
Single-action pumps are frequently used in hydraulic
Several types of power-operated hydraulic pumps,
such as the radial piston (fig. 3-14) and axial piston
(figs. 3-15 and 3-16), are classified as reciprocating
pumps. These pumps are sometimes classified as
rotary pumps, because a rotary motion is imparted to
the pumps by the source of power. However, the actual
pumping is performed by sets of pistons reciprocating
inside sets of cylinders.
It is all but impossible to design a practical fluid
power system without some means of controlling the
volume and pressure of the fluid and directing the flow
of fluid to the operating units. This is accomplished by
incorporating different types of valves. A valve is
defined as any device by which the flow of fluid may
be started, stopped, or regulated by a movable part that
opens or obstructs passage.