Copyright Goodheart-Willcox Co., Inc.
Chapter 6 Cylinders 133
can be confi gured with one narrow wear ring, one wide wear ring, or two narrow
wear rings. Wear rings are commonly made of nylon. See Figure 6-14.
A piston seal is installed around the outside circumference of the piston.
The piston seal’s job is to maintain a fl uid-tight seal between the barrel and
piston as the piston slides in and out of the barrel. Piston seals vary in com-
position and design. A few factors that manufacturers must consider when
choosing a seal is the compatibility of the oil, fl uid temperature, seal longevity,
cylinder speed, and pressure. Piston seals designs can be categorized into three
groups:
• Metal seals.
• Double-acting seals.
• Lip seals.
Seal design and composition determine the effectiveness, durability, and
leakage potential of the piston seal. For example, metal seals will leak the most,
but are more durable and longer lasting. Metal seals can be steel, cast iron, or
chrome-plated steel.
Piston
wear ring
Piston
Piston seal Clevis
Removable
gland
Rod seal
Wear ring
Port A
(extension)
Port B
(retraction)
Wiper/
scraper
Figure 6-12. This articulated dump truck uses two double-acting telescoping cylinders to dump the bed. The fluid
passageways are drilled through the plunger and stages.
Figure 6-13. A cylinder contains a piston, rod, gland, barrel, and clevis. The piston requires a wear ring and seal.
The gland requires a rod seal and a wiper.