Piston

The main function of the piston is to separate the pressure zones inside the barrel. The piston is machined with grooves to fit elastomeric or metal seals and bearing elements. These seals can be single-acting or double-acting. The difference in pressure between the two sides of the piston causes the cylinder to extend and retract. The piston is attached to the piston rod by means of threads, bolts, or nuts to transfer the linear motion.

Piston rod

The piston rod is typically a hard chrome-plated piece of cold-rolled steel that attaches to the piston and extends from the cylinder through the rod-end head. In double rod-end cylinders, the actuator has a rod extending from both sides of the piston and out both ends of the barrel. The piston rod connects the hydraulic actuator to the machine component doing the work. This connection can be in the form of a machine thread or a mounting attachment. The piston rod is highly ground and polished so as to provide a reliable seal and prevent leakage.

Seal gland

The cylinder head is fitted with seals to prevent the pressurized oil from leaking past the interface between the rod and the head. This area is called the seal gland. The advantage of a seal gland is easy removal and seal replacement. The seal gland contains a primary seal, a secondary seal/buffer seal, bearing elements, a wiper/scraper, and a static seal. In some cases, especially in small hydraulic cylinders, the rod gland and the bearing elements are made from a single integral machined part.

Other parts

There are many component parts that make up the internal portion of a hydraulic cylinder. All of these pieces combine to create a fully functioning component.[9]

Cylinder base connection

Cushions

Internal Threaded Ductile Heads

Head Glands

Polypak Pistons

Cylinder Head Caps

Butt Plates

Eye Brackets/Clevis Brackets

MP Detachable Mounts

Rod Eyes/Rod Clevis

Pivot Pins

Spherical Ball Bushings

Spherical Rod Eye

Alignment Coupler

Ports and Fittings

Single acting vs. double acting

Further information: Single- and Double-acting cylinder

Single-acting cylinders are economical and the simplest design. Hydraulic fluid enters through a port at one end of the cylinder, which extends the rod by means of area difference. An external force, internal retraction spring or gravity returns the piston rod.

Double acting cylinders have a port at each end or side of the piston, supplied with hydraulic fluid for both the retraction and extension.

Seals

Main article: Hydraulic seal

The seals are considered/designed to withstand maximum cylinder working pressure, cylinder speed, operating temperature, working medium, and appliEion. Piston seals are dynamic seals, and they can be single-acting or double-acting.[8] Generally speaking, Elastomer seals made from nitrile rubber, Polyurethane, or other materials are best in lower temperature environments, while seals made of Fluorocarbon are better for higher temperatures. Metallic seals are also available and commonly used cast iron for the seal material. Rod seals are dynamic seals and generally are single-acting. The compounds of rod seals are nitrile rubber, Polyurethane, or Fluorocarbon . Wipers/scrapers are used to eliminate contaminants such as moisture, dirt, and dust, which can cause extensive damage to cylinder walls, rods, seals, and other components. The common compound for wipers is polyurethane. Metallic scrapers are used for sub-zero temperature appliEions and appliEions where foreign materials can deposit on the rod. The bearing elements/wear bands are used to eliminate metal to metal contact. The wear bands are designed to withstand maximum side loads. The primary compounds used for wear bands are filled PTFE, woven fabric reinforced polyester resin, and bronze

Designs

There are primarily two main styles of hydraulic cylinder construction used in the industry: tie rod-style cylinders and welded body-style cylinders.