Figure 3-25.The basic operation of a simple poppet valve.
cylinder in which the cross-sectional area of the piston
is less than one half of the cross-sectional area of the
movable element is referred to as a piston-type
cylinder. This type of cylinder is normally used for
applications that require both push and pull functions.
The piston-type cylinder is the most common type
used in fluid power systems.
The essential parts of a piston-type cylinder are a
cylindrical barrel, a piston and rod, end caps, and
suitable seals. The end caps are attached to the end of
the barrel. These end caps usually contain fluid ports.
The end cap on the rod end contains a hole for the
piston rod to pass through. Suitable seals are used
between the hole and the piston rod to keep fluid from
leaking out and to keep dirt and other contaminants
from entering the barrel. The opposite end cap of most
cylinders is provided with a fitting for securing the
actuating cylinder to some structure. This end cap is
referred to as the anchor end cap.
Figure 3-26.Operation of a rotary spool valve.
The piston rod may extend through either or both
ends of the cylinder. The extended end of the rod is
normally threaded so that some type of mechanical
connector, such as an eyebolt or clevis, and locknut can
be attached. This threaded connection provides for
adjustment between the rod and the unit to be actuated.
After the correct adjustment is made, the locknut is
tightened against the connector to prevent the
connector from turning. The other end of the connector
is attached to, either directly or through additional
mechanical linkage, the unit to be actuated.
To satisfy the many requirements of fluid power
systems, piston-type cylinders are available in various
designs with the most common being the single- (fig.
3-30, view A) and double-acting (fig. 3-30, view B).