Chapter 6 Cylinders 127
Copyright Goodheart-Willcox Co., Inc.
Double-Acting Cylinders
A double-acting cylinder uses fluid r pressure to extend the cylinder and fl
fl uid pressure to retract the cylinder. The most common type of double-acting fl
cylinder is equipped with a single rod. Another name for this actuator is a
differential cylinder, due to the piston area differences. See r r Figure 6-3. The
rod side of the piston has less effective area because a portion is displaced
by the cylinder’s rod, resulting in an effective area that resembles a ring. The
ring’s area is always less than the cap side of the piston.
Another term that is used to frequently describe one side of a cylinder is
“head end.” The International Fluid Power Society (IFPS) specifies the rod end fi
of the cylinder as the head end, and the opposite end as the d cap end, or blind d
end. In contrast, Caterpillar and John Deere’s Construction and Forestry (C&F)
division frequently label the side that is opposite the rod end as the head end.
To avoid confusion resulting from different agencies using the term in different
fashions, this text will not use the term ”head end.” Instead, it will identify the
cylinder ends as the rod end and the cap end.
Figure 6-2. A single-acting cylinder can be designed to hydraulically retract the cylinder, with a weight used to extend
the cylinder. However, this application is rare.
Figure 6-3. A double-acting cylinder uses fluid pressure to extend and to retract a cylinder. The area of the ring side
of the cylinder piston (pink) is smaller than the area of the piston’s cap side. Note that the cross-sectional area of the
rod is subtracted from the total area on the piston’s ring side.
Rod end Cap end
Ring area