cylinders is provided with a fitting for securing the
actuating cylinder to some structure. For obvious
reasons, this end cap is referred to as the anchor end cap.
The piston rod may extend through either or both
ends of the cylinder. The extended end of the rod is
normally threaded for the attachment of some type of
mechanical connector, such as an eyebolt or a clevis, and
a locknut. This threaded connection of the rod and
mechanical connector provides for adjustment between
the rod and the unit to be actuated. After correct
adjustment is obtained, the locknut is tightened against
the connector to prevent the connector from turning. The
other end of the eyebolt or clevis is connected, either
directly or through additional mechanical linkage, to the
unit to be actuated.
To satisfy the many requirements of fluid power
systems, you may get piston type cylinders in various
designs. Two of the more common designs (fig. 10-13)
are described in the paragraphs below.
Single-Acting Piston. The single-acting
piston-type cylinder (fig. 10-13, view A) is similar in
design and operation to the single-acting ram-type
cylinder previously covered. The single-acting
piston-type cylinder uses fluid pressure to apply force
in only one direction. In some designs of this type, the
force of gravity moves the piston in the opposite
direction; however, most cylinders of this type apply
force in both directions. Fluid pressure provides the
force in one direction, and spring tension provides the
force in the opposite direction. In some single-acting
cylinders, compressed air or nitrogen is used instead of
a spring for movement in the direction opposite that
achieved with fluid pressure.
The end of the cylinder opposite the fluid port is
vented to the atmosphere. This prevents air from being
trapped in this area. Any trapped air would compress
during the extension stroke, creating excess pressure on
the rod side of the piston. This would cause sluggish
movement of the piston and could eventually cause a
complete lock, preventing the fluid pressure from
moving the piston.
You should note that the air vent ports are normally
equipped with an air filtering attachment to prevent
ingestion of contaminates when the piston retracts into
A three-way directional control valve is normally
used to control the operation of this type of cylinder. To
extend the piston rod, fluid under pressure is directed
through the port and into the cylinder. This pressure acts
on the surface area of the blank side of the piston and
forces the piston to the right. This action, of course,
extends the rod to the right through the end of the
cylinder. This moves the actuated unit in one direction.
During this action, the spring is compressed between the
rod side of the piston and the end of the cylinder. Within
limits of the cylinder, the length of the stroke depends
upon the desired movement of the actuated unit.
Double-Acting Piston. Most piston type actuating
cylinders are double-acting, which means that fluid
under pressure can be applied to either side of the piston
to provide movement and apply force in the corre-
One design of the double-acting piston type
actuating cylinder is illustrated in figure 10-13, view B.
This cylinder contains one piston and piston rod
assembly. The stroke of the piston and piston rod
assembly in either direction is produced by fluid
pressure. The two fluid ports, one near each end of the
cylinder, alternate as inlet and outlet, depending upon
the direction of flow from the directional control
This is referred to as an unbalanced actuating
cylinder; that is, there is a difference in the effective
working areas on the two sides of the piston. Assume
that the cross-sectional area of the piston is 3 square
inches and the cross-sectional area of the rod is 1 square
Figure 10-13.-Example of piston type of cylinder.